(DSP-based LiMCA
system)
LIQUID METAL STUDIES
MATHEMATICAL & PHYSICAL MODELLING OF
METALLURGICAL PROCESSES
SOLIDIFICATION STUDIES
SOLID METAL PROCESSING STUDIES
ENERGY & ENVIRONMENT IN METALS PROCESSING
TEXTURE & PROPERTIES OF ENGINEERING MATERIALS
PROCESSING
& CHARACTERIZATION OF POLYMERS
Research Related to Liquid Metal Quality Studies
Thanks to break-through technology at McGill in the early 1980’s, it is now possible to monitor the quality of liquid metals in terms of the numbers of extraneous inclusions. Thus, LiMCA(Liquid Metal Cleanliness Analyzer) sensors make use of the electric sensing zone principle to detect inclusions within a sample of liquid metal drawn into an electrically insulated sampling tube. First conceived and developed at McGill University, rugged commercial versions of the instrument were later designed and assembled by Bomem Inc., and successfully used in Alcan's casting centres around the world.
(DSP-based LiMCA
system)
A second version, LiMCA II, has since been constructed and made available in 1994 for the Aluminum Industry. Bomem and Alcan, received a prestigious R&D 100 Award that year from R&D magazine, LiMCA II being voted one of the most technologically significant products of 1994. In the meantime, the study of liquid metal quality at McGill using our own equipment has continued, aimed at extending the technique’s application to other metals, such as alloys of copper, magnesium and most importantly, liquid steel. Similarly, we have been researching means to enhance the analytical power of the resistive pulse principle, so as to allow us to discriminate between different types of inclusions within a melt. In aluminum, for example, microbubbles are relatively harmless compared with carbide or silicate inclusions, and need to be distinguished from a metal quality control point of view. To do this, we have pioneered the application of digital signal processing technology (DSP) which, combined with pattern recognition techniques, provides the necessary processing capability in analyzing the voltage pulses generated by the passage of particles through the electric sensing zone.
LiMCA in Other Metals
Magnesium
A prototype LiMCA probe
suitable for use in melts of magnesium has finally been developed.
The novel probe, comprising a pair of spring-loaded concentric steel tubes
separated by a ceramic orifice disc, has been tested successfully in our
laboratories and later, in Timminco’s pilot scale melting furnace.
Further tests in Timminco’s new holding furnace are projected. The
preliminary work is described in two conference proceedings; Light Metals
1997 Métaux Légers - Sudbury, MetSoc of CIM, and the 1st
Israeli Int’l Symposium on Magnesium Science and Technology. Patents
have now issued in US and Canada for the magnesium inclusion sensor probe.
Industrial collaborants to date have included Norsk Hydro, Timminco and
CSIRO Australia.
Liquid Steel
In-plant and laboratory
experimental work for the testing of a “one-shot” LiMCA probe for steel
was completed by H.C. Lee, who received his Ph.D. in 1994. The success
rate of the probe was encouraging, its design being simplified in order
to reduce the cost of the instrument. Since
that time, extensive development work by Electronitehas lead to the production
of commercially available probes as of 2003AD, suitable for carbon, and
specialty, steels (bearing grades). is now available. This new era for steel
quality control is presented at this Year’s review, by Dr Rick Conti,
Electronite’s Director of Research, and Dr Hidemasa Nakajima, General Manager
of Iron and Steelmaking plant, KOKURA Works.
Digital Signal Processing for LiMCA Signal Classification & Particle Discrimination
The two objectives of this research were met in 1999: (1) MetalWindows™ a Windows-based software for the on-line DSP-based acquisition, processing and analysis of LiMCA signals is now available. Version 1.0 of the user-friendly software includes printing, report-generation, and calibration features. (2) Considerable progress was made in understanding the characteristic differences between the passage of gas bubbles and solid particles through the electric sensing zone (C. Carozza and Mei Li). On-going efforts aim to establish relationships between the different physical phenomena at the orifice of the LiMCA probe and to integrate latest advances in signal discrimination into MetalWindows.™ The DSP-based LiMCA has a number of potential advantages in terms of cost and flexibility compared to the existing LiMCA II analogue based technology. Supporting industrial partners to this work, which was funded by an NSERC Strategic grant, comprised Electro-Nite, Timminco and Bomem, provided the software platform for the design of Electronites Probe. On-going development work at the MMPC plans to rework the in-house LiMCA system with software and hardware upgrades, given the Ariel DSP board of its original equipment is no longer manufactured.
Magneto-hydrodynamic Analysis of Limca Systems
The passage of an inclusion through the electric sensing zone orifice in a metallic system is quite different from an equivalent aqueous system, in that the heavy currents involved (~20-50 A) and narrow passage (~ 100-1000 mm), gives rise to the so-called “magnetic pinch” effect. This creates a radial magnetic field gradient and radial force, FR, that radially accelerates non-conducting particles out to the sidewalls of the electric sensing zone (FR = p m0 j2 a3 r, where m is the permeability constant, j the current density, a inclusion radius and r the radial distance of the inclusion from the axis).
(60 A, 300um dia. Parabolic ESZ) (250
A, 300um dia. Parabolic ESZ)
Depending on the size and density of the inclusions, this radial acceleration can be more, or less important. Previous and current literature has claimed that the application of ESZ (Electric Sensing Zone) technology to liquid metals is theoretically impossible since the sidewalls of the sensing zone will act as a collecting surface for non-conducting inclusions being forced outwards. Mei Li developed a generalized mathematical model capable of describing the trajectory of particles (inclusions) through the ESZ, based on their entry path, the shape and axial length of the ESZ, and physical and electrical properties of the melt and inclusions. Current work on LiMCA (JinXi Li) involves direct physical measurement of the electromagnetic forces induced in a molten metal, and the role of orifice shape on these force fields. As seen in the diagram, flow fields can be reversed when heavy currents of 250A are used vs ‘moderate’ currents of 60A pertaining to normal operating procedures. However, the role of orifice shape is a key factor in creating these reverse flows, which are used to “condition” the orifice prior to sampling of the melt.
Grain Refining Studies by Limca
Limca technology has been extended to the analysis of grain refining additions of titanium diboride (TiB2) to aluminum silicon casting alloys. Through DSP technology, we have conclusively demonstrated that TiB2 additions to aluminum casting alloys, by themselves, have no grain refining capability, and can be recognized by the negative voltage pulses they generate when passing through the ESZ zone. The explanation for this is that TiB2 has a greater electrical conductivity vs. aluminum, so that the electrical current flows more easily through such inclusions, thereby generating negative peaks (or voltage transients). In the presence of excess titanium (~ 2 wt%) however, signals are positive, and grain refining capability is observed. This observation reinforces the hypothesis that a layer of TiAl3 coats TiB2 particles, and is needed for epitaxial growth of nucleating grains of aluminum.
Lead Solders for Electronic Circuit Boards
The use of lead solders for electronic circuit boards for the computer industry is widespread. Preliminary Limca experiments on a free flowing low viscosity (63% Sn, 37% Pb) solder (Hi-flow) has proved that these alloys have far less inclusions (40 times less) versus regular solders that exhibit poorer coating abilities. This work was carried out for Alpha Fry of the Cookson Group.
Limca for Al-Si Foundry Alloys and Die Castings
Studies by C.Carozza and R.Sankaranarayanan were performed to test the metal quality of scrap Al-Si AA335 N transmission die casting alloys versus virgin aluminum foundry alloys. It was shown that metal quality from scrap die castings was significantly lower than the levels in primary ingot feedstock stock (e.g. 60,000 K/kg vs. 1,000 to 10,000 K/kg inclusions greater than 55 microns diameter), and that Limca technology could be applied to such operations. This work was carried out for CSIRO-Nissan Castings, Australia who have subsequently acquired a Limca II machine. Several conference papers have been written by our group concerning the good correlation between melt quality and porosity formation in Al-Si foundry alloys.
Limca for Filtration/Settling Studies
On the basis of aluminum metal quality measurements, upstream, and downstream, of Hi-Tech ceramic foam filters installed at Eastalco, mathematical models of the dynamic filtration process were developed, that reflect and predict the performance of such filters in improving metal quality. These models, developed by Dr. Chenguo Tian for his Doctorate at McGill, are described in a number of proceedings and in a summary article in Metallurgical Transactions.
MATHEMATICAL & PHYSICAL MODELLING OF METALLURGICAL PROCESSES
A variety of projects involving hydrodynamic and transport phenomena in liquid metal processing operations have been studied. The fluid, heat, and mass transfer, components deal with basic aspects of the mathematical and physical modelling of multi-phase, multi-dimensional flows in systems of metallurgical interest (e.g. furnaces, ladles, tundishes, twin roll casters, single belt casters, settling tanks, etc.). Thanks to our new full scale ladle-tundish-mould facility now under construction, much of the reduced scale modeling work described in this section will be repeated at the full scale. This will be very helpful in confirming, and extending, the design principles and results described below.
Modelling of Slag Entrainment during the Emptying of Metallurgical Vessels
The role of various operating parameters in the formation of “vortexing” and “non-vortexing” funnels, which entrain slag during ladle-teeming operations, has been studied experimentally. Models have been developed to predict slag entrainment behaviour in other vessel geometries and drainage conditions, in keeping with the vessels used in the continuous casting of steel. In collaboration with Vesuvius and Foseco, the role of inclined bottom surfaces of ladles in the formation of late forming vortexing funnels has been studied. Results suggest that off-centred nozzles placed in sloping ladles bottoms to help increase steel yield lead to higher critical heights for vortexing funnels, i.e. impaired steel quality. Currently, the performance of Dofasco’s 340 ton-ladle shroud/slide gate system is being studied, at full scale, to determine critical vortexing heights and means to improve steel quality.
Modelling of Two Phase Flows in Ladle Shroud Systems
In collaboration with Dr. J.D. Usher, the entrainment of air into steel flowing in the ladle shroud to the tundish was modelled, for water velocities ranging between 0.4 and 2 m/s through a 53 mm ID ladle shroud, 1.2 metres long. It was demonstrated that at low percentage volumes of gas within the shroud, small bubbles form whose terminal rising velocities are less than the downflow velocity of the liquid. This gives rise to a uniformly dispersed array of downwards moving bubbles, termed the ‘bubbly flow’ regime. At higher air entrainment ratios and low water velocities of 0.4 m/s (corresponding to a three quarter way closed slide gate nozzle setting for example), flow through the shroud separates from the walls, a large gas cavity filling the upper half of the shroud. At liquid velocities of 2 m/s and fractional gas volumes of about 5%, the bubbly flow regime transforms into a bubbly-slug flow condition, while at still higher rates of air entrainment in the order of 10% fractional volume (corresponding to a cracked shroud for example), an air core forms, with liquid draining down the sidewalls of the shroud. These observations are important with respect to the placement of wire inserts into the sidewalls of ladle shrouds, used for the detection of slag carryover. The new water modelling facilities now allow us to re-study at the full scale, and at equivalent vacuum levels for air aspiration into the shroud, using the 10m high “pop-up” facility, and the ladle shroud/slide gate nozzle set up for Dofasco’s operations.
Physical Modelling of Advanced Tundish Vessels
The aim of this comprehensive project is to develop detailed physical and supporting mathematical models incorporating 3D turbulent flow, mixing, heat transfer and inclusions distribution, in tundishes. Two full-scale tundishes have been built (four and six strand delta designs) in order to test the performance of the various flow control devices used for assuring metal quality. Tests on critical vortexing heights during tundish emptying and refilling operations have been made, together with residence time distribution curves as a function of flow rates, impact pad designs, nozzle’s well blocks, gas entrainment levels in ladle shroud, etc.
These studies at the full scale allow for better design and control of secondary steel processing vessels, in order to design vessels that prevent harmful impurities entering the casting mould. It is particularly helpful, in this regard, to be able to install geometrically equivalent metering nozzles, ladle shrouds and SEN’s, as well as tundish “furniture.” The flow system is capable of handling flows of up to 600 litres/min, as will as being able to model thermal variationsin the entering stream.
Physical and mathematical simulations of Flow, Temperature and Compositional Variations in a Continuous Galvanizing Bath
Continuing sponsorship by the International Lead Zinc Research Organization (ILZRO) has now allowed a well recognized research team from Ecole Polytechnique and NRC-Industrial Materials Institute (IMI) to be built up. This team is now carrying out numerical simulations of the flow of molten zinc, and attendant heat and mass transport, within a continuous galvanizing bath. These computations were verified through experimental water modelling studies at McGill last year, using the MMPC’s PIV equipment. Local velocity variations were thereby determined, and found to be very close to those simulated numerically, confirming the validity of the numerical method. The results of this validation study also clearly showed that both the natural convection, generated by the small density differences of water as a function of temperatures, as well as forced convection, are essential for precise simulation of bath flows.
These results were presented at the
AIST Galvatech 04 Conference in
Effect of metallurgical parameters on the mechanical properties in 319 alloys
The present work was performed on four alloys containing Al-6.2 wt pct Si-3.5 wt pct Cu, with magnesium in the range of 0.02-0.40 wt pct, and strontium in the range 0-165 p.p.m. Tensile bars were cast in a permanent mold (ASTM B108-160) and heat treated at 495ºC for 4 and 24 hours, followed by quenching in hot water. Two different artificial aging temperatures were applied at 180 ºC and 220 ºC for times from 0.5 h up to 24 h. Tests were conducted with the intent of determining how the mechanical properties of an aluminum-based 319 alloy are affected when aging time and temperatures are varied. Microstructural examination was carried out using optical microscopy, image analysis, and electron probe microanalysis (EPMA), with energy dispersive X-ray (EDX) and wavelength dispersive spectroscopic (WDS) analysis facilities. The study of fine precipitate characterization is being carried out by transmission electron microscopy. In general, it is seen that the alloy does not exhibit the common peak-overaged aging condition due to the presence of several coexisting phases, indicating that they form through complex eutectic reactions late in solidification. The addition of Mg (~0.40 wt %) leads to the precipitation of coarse Al5Mg8Si6Cu2 particles. Sr-modification of the high Mg alloys leads to segregation of Cu-intermetallics in areas away from the growing Al-Si eutectic regions.
Extended Metal Delivery Systems for Horizontal Belt Casting Processes
In collaboration with the Hazelett Strip Casting Corporation, BHP and other member companies of the International Advisory Board, a pilot scale horizontal belt caster has been installed in the new foundry of the M.H. Wong Building. The purpose of this machine will be to test various metal delivery systems for the production of thin strips of low carbon steels, copper alloys, and lower melting point metals such as aluminum and magnesium alloys. This data is needed to confirm the practicability of using extended nozzle systems, to test the effects of various belt substrate coatings on surface quality, to determine strip microstructures, to test the viability of such a machine for the high speed production of steel strip in the 10-20 mm thickness range, and to compare experimental results with our predictions for such systems, based on the mathematical models described below.
Modelling of Planar Thin-Strip Steel Casting Processes
A mathematical model comprising coupled heat transfer and fluid flow has been developed by P. Netto to describe two and three dimensional turbulent flow of metal in a planar thin-strip continuous-casting system for steel. The system consists of a reservoir, an extended nozzle containing a reticulated porous filter (flow modifier), a cooled moving substrate and an outlet region. The governing transport equations were solved numerically using the control-volume based finite-difference scheme, incorporating the SIMPLER algorithm. The generated temperature fields were input on a version of a finite-element method to calculate the stress fields and relevant displacements on the solidifying shell. Using the model, the roles of (1) the speed of the substrate, (2) cooling conditions of the substrate, (3) dimensions of the porous filter in the nozzle zone, (4) convective and radiative heat-transfer coefficients, (5) temperature of the surrounding atmosphere, (6) geometrical aspects of the delivery system and (7) turbulent flow in the nozzle zone, were studied. Comparisons with low-temperature physical models confirmed predicted flows.
(Temperature profile in the reservoir)
Strip Casting Simulator for Direct Steel Casting (DSC) Systems
As an adjunct to the mathematical modelling, an experimental apparatus has been developed for the determination of heat fluxes and heat-transfer coefficients between a solidifying strip and a moving substrate covered with various coatings, so that realistic boundary conditions can be applied in the mathematical modelling simulations. This experimental work has the objective of determining the influence of the most important parameters on the heat transfer: Thickness of the strip, superheat, substrate speed, nature of the coating and roughness of the substrate surface. It has been shown that transient heat fluxes are highly time and position dependent. Studies carried out by M. Isac, P. Netto, R. Tavares, J. Kim, J. Byun and R.I.L. Guthrie on the influence of solidification and heat transfer on strip microstructure were published in the Sudbury and Toronto Proceedings of the Light Metals division of CIM and received the 1997and 2000 Light Metals Best Paper Awards. J. Kim is continuing these studies and upgrading the equipment, so that wider, longer, sections of strip, and attendant microstructures, can be studied. This project is supported financially by an NSERC strategic grant, for the next four years 2002 – 2006.
(Microstructure of transverse section
of Al-Si alloy strip)
Mathematical and Process Modelling of a Vertical Twin-Roll Caster
A three-dimensional mathematical model coupling turbulent fluid flow, heat transfer and solidification has been developed by R. Tavares for a vertical twin-roll thin-strip casting process. For turbulence, a low Reynolds k-e model has been adopted. To solve the discretized form of the conservation equations, the METFLO code, developed in house, was used. Different casting conditions and metal delivery systems have been simulated and their effects on the formation of the solidified shell have been analyzed. Physical modelling using a full scale water model was used to validate the fluid flow computations.
This work has demonstrated that conventional SEN’s (submerged entry nozzles) lead to non-uniform shell growth in the transverse direction. Vertical slot nozzles help greatly in this regard, but it was demonstrated that low velocity radial outflow through an extended nozzle provide the best condition to asure uniform shell development, minimal surface turbulence and premature freezing of liquid state at the menisci in contact with the rotating rolls.
Measurement of Interfacial Heat Fluxes in Twin Roll Caster (TRC) Systems
In collaboration with the IMI Group at Boucherville, working on Projet Bessemer, actual temperatures were measured at different points close to the surface of the casting rolls. Based on these temperatures, a methodology for evaluation of heat fluxes at the roll surface was developed by R.P. Tavares. These heat fluxes were used as the boundary condition in our models. The variation of the heat flux during the contact time between the roll and the solidified shell improved our understanding of the heat transfer phenomena taking place in the roll gap. It was found that heat fluxes to the roll surfaces were highly position dependent, heat fluxes at the meniscus being low, rising to a maximum towards the mid-depth region, followed by a sharp drop off before the role nip. For thicker strips (~ 4 mm thick), a secondary peak heat flux was observed, which is believed to be caused by the intermeshing of the two advancing dendritic regions of the freezing shells as well as a certain amount of “rolling” work. Our work has demonstrated the critical role of melt delivery in assuring uniform transverse properties, as mentioned above.
Finally, in the same study, a microsegregation model coupled with heat transfer, has been developed and has been used to predict austenite grain sizes of the strips after the solidification process. These simulations show that grain sizes in the order of 300-400 um are formed for 2 mm strip exiting the rolls. Microstructure analyses such as SDAS and austenite grain size microstructures carried out by M. Isac, were used to validate the microsegregation model. This was confirmed from strip samples, and points to the inherent difficulty of currently proposed TRC systems for low carbon steels, in providing fine grained products.
Coupled Turbulent Flow and Solidification Heat-Transfer Modelling of Continuous Casting of Slabs
A two-dimensional simulation of turbulent fluid flow and heat transfer has been developed by Dr. R. Aboutalebi to describe the coupled turbulent flow and heat transfer with solidification in the mould and secondary cooling zone of Dofasco's continuous steel slab caster. The turbulence was modelled using a low-Reynolds k-e model. Parametric studies were carried out to determine the effects of different parameters such as delivered superheat and the type of nozzle, on the velocity and temperature fields and solidified shell thickness. The numerical predictions of velocity and temperature fields were found to compare favourably with existing data from the water-modelling and experimental results reported in the literature.
A three-dimensional numerical investigation was also conducted for exploring the steady state transport phenomena of turbulent flow, heat transfer and macroscopic solidification in a continuous stainless steel slab caster. The numerical model was based on a generalized transport equation applicable to all the three regions, namely liquid, mushy and solid, which exist in a slab caster. The turbulence effects on the transport equations were taken into account using a low-Reynolds number turbulence model. The solidification of molten steel was modeled through the implementation of the popular enthalpy-porosity technique. A control volume based finite-difference scheme was used to solve the modeled equations on a staggered grid arrangement. A series of simulations was carried out to investigate the effects of the casting speed, the delivered superheat and the immersion depth of the twin-ported submerged entry nozzle (SEN) on the velocity and temperature distributions and on the extent of the solidified and mushy regions on the narrow and broad faces of the caster. In the absence of any known experimental data related to velocity profiles in a slab caster, the numerical predictions of the solidified profile on a caster’s narrow face were compared with limited experimental data and a good agreement was found.
Towards bulk amorphous sheet materials on a single belt caster?
Currently, the production of steel and aluminum sheet for the transportation and appliance sectors is dominated by fixed mould continuous casting technologies; i.e the oscillating, fixed mould slab caster for steel sheet products, and the direct chill (DC) casters of the aluminum industry. The present research being carried out in collaboration with Questek, looks to the friction free casting of metals, and concerns the chances of producing bulk amorphous sheet materials off near-net shape casting machines. “Glassy”, or amorphous alloys, can exhibit unusual and promising combinations of metallurgical properties in terms of higher Ultimate Tensile Strength (UTS) and hardness, improved resistance to both fatigue and corrosion, and for ferrous alloys, improved magnetic susceptibility, versus equivalent crystalline materials. Similarly, such a structure can act as an ideal precursor for nano-grain material with superior strength and high temperature properties. Metallic glasses can be formed if a melt can be cooled sufficiently rapidly so that the heterogeneous nucleation of crystals can be avoided until a “Glass Transition Temperature” is reached. Under such conditions the material transforms into a solid without atoms assuming fixed lattice positions characteristic of a solid. Many bulk amorphous alloys with relatively modest cooling rate requirements (<103 K/s) have been found for multi-component systems such as Mg-Ln-TM, Ln-Al-TM and Zr-Al-TM. The various systems are summarized in Table I, where Ln represents the lanthanide metals and TM the group VI-VIII transition metals. To date, it has been possible to produce much thicker amorphous alloys for non-ferrous metals as compared to ferrous systems. In this regard, the series of aluminum-gadolinium-nickel alloys in the Ln-Al-TM group are of particular interest, since aluminum is the main component, in the range 80-90 atomic %. Table 1 indicates that 10mm thick material has been produced in this family of alloys.
|
I. Non-ferrous Metal Base |
Years |
tMAX (mm) |
|
Mg-Ln-M |
1988 |
10 |
|
Ln-Al-TM |
1989 |
10 |
|
Ln-Ga-TM |
1989 |
10 |
|
Zr-Al-TM |
1990 |
30 |
|
Ti-Zr-TM |
1993 |
3 |
|
Zr-Ti-TM-Be |
1993 |
25 |
|
Zr-Ti-Al-TM |
1995 |
20 |
|
Pd-Cu-Ni-P |
1996 |
72 |
|
Pd-Cu-B-Si |
1997 |
10 |
|
II. Ferrous Metal Base |
Years |
tMAX (mm) |
|
Fe-( |
1995 |
3 |
|
Fe-(Nb,Mo)-( |
1995 |
3 |
|
Co-( |
1996 |
1 |
|
Fe-(Zr,Hf,Nb)-B |
1997 |
5 |
|
Co-(Zr,Hf,Nb)-B |
1997 |
1 |
|
Ni-(Zr,Hf,Nb)-B |
1997 |
1 |
|
Fe-(Co,Ni)-(Zr,Hf,Nb)-B |
1997 |
6 |
Selected multi-component alloy systems with large GFA (glass forming ability)
Fundamental heat transfer analyses
(J.S. Kim, D-H Li, M.Isac, R.Guthrie) were carried out last year, exploring the
possibility of casting bulk amorphous sheet material, in twin roll casters,
and/or belt casters. Given an alloy’s thermal conductivity, heat capacity, and
density, and those of the cooling substrate, it is possible to develop analytical
expressions for determining the glass temperature-critical cooling rate
boundary separating crystalline material, from the glassy state. The key
parameter to the successful casting of amorphous sheet material lies in control
of the interfacial thermal resistance between the freezing sheet and the
cooling substrate. Various experiments were carried out by Dr. Dong-hui Li and
Thermal Analysis of Aluminum Alloys
Thermal analysis is a developing tool for quality control in the aluminum industry. Current use is restricted to grain size control and in some cases the determination of the extent of eutectic modification. The aims of the present research are to push the thermal analysis technique to its limits by using it to estimate the volume percentage of intermetallic phases, such as iron bearing intermetallics in addition to developing the technology for more precise control of modification and grain refinement. Techniques under investigation include the use of derivative curves (first and second) in addition to the regular temperature-time plots. While the project aims mainly at understanding thermal analysis in aluminum foundry alloys, certain wrought alloys are also under study.
A particular feature of the thermal analysis studies at McGill is the use of heat pipes to cool the sample during analysis. A semi-continuous thermal analysis apparatus has been developed which is capable of doing analysis at controlled and variable cooling rates throughout the entire cooling process.
Porosity Formation in Low Pressure Casting
The formation of porosity in low pressure aluminum castings is poorly understood. The objective of this project is to develop criteria functions to allow porosity level predictions in terms of the thermal parameters during solidification. Thermal parameters are computed from models of low pressure cast plates into which thermocouples have been embedded. Porosity measurements made on these plates are then correlated with the thermal conditions existing before solidification. A variety of aluminum casting alloy is being studied with several conditions of melt treatment such as modification, degassing and grain refinement. This project is carried out in conjunction with a large Ontario foundry specializing in the low pressure casting process.
Associated with the study of porosity in low pressure castings is work dedicated to a more fundamental understanding of the porosity formation process in cast aluminum alloys. This includes an assessment of existing physical models for the formation of porosity, and the development of new models better able to predict quantitatively the development of porosity in industrial castings.
Metastable Phases in DC Cast Ingots
The condition for formation and solidification characteristics of the metastable phases occurring in DC ingots will be studied. It is desired to define the exact growth conditions for transformation form the stable to the metastable condition and to relate those to the actual conditions occurring in a DC ingot. This project was conducted in collaboration with Alcan and l’Université du Québec à Chicoutimi.
Calcium Modification of Aluminum-Silicon Foundry Alloys
A systematic study of the use of calcium as a eutectic modifier is underway. Although calcium is known to modify, the details of its use are not clear. This project aims to clarify such questions as: Optimum calcium level, relationship between cooling rate and calcium concentration required for modification, fading, effect of calcium on porosity formation in castings. The interest in calcium stems from its abundance and low cost.
Riser Design Optimization
Considering the use of simulation to predict and improve both quality and profitability of casting production, one might reasonably ask how the design process can be improved so that an optimum process design can be obtained. One approach which has very recently been implemented in software is the application of multi-variable response surface optimization to casting simulation. In this technology, an optimization engine is used to evaluate the results of a series of simulations, making decisions as to what needs to be changed at each iteration until a design is found which allows a specific objective to be achieved.
(AlSi7Mg03 cluster of 4 plate castings with ¼” round specimens)
SOLID METAL PROCESSING STUDIES
Characterisation and Mechanical Properties
Cast and formed alloys and composites were analysed for casting defects such as porosity surface finish, mould filling capacity and segregation of particles using both optical and electronic facilities for their characterisation. Mechanical properties such as tensile tests, hardness were also carried out on cast samples with different heat treatments (T5 and T6). The properties were then related to the processing conditions to determine the window of operating parameters for obtaining sound components using this technology.
A study of the characteristics of semi-solid forming of Mg-Al alloys is presently carried out by Faouzi Messaoud as part of a Ph.D. project. The objective is to determine the rheological and morphological evolution of this family of alloys during continuous cooling experiments and for isothermal measurements at various shear rates. Relationships of the variation of the apparent viscosity with shear rate, solid fraction and duration of shear will be established to develop models describing the thixotropic behaviour. Comparisons will be made with previously established models for Al-Si and composite semi-solid alloys. This fundamental data is essential for the establishment of the operating window for the forming of these alloys in a thixomoulding or die casting machines, as well as for numerical modeling of mould filling of specific components.
Summary of Work on Oxidation/Decarburization of Selected Steels during Reheating
During reheating of steel slabs in a walking-beam steel reheat furnace, it was observed that scaling rates can be reduced by lowering input air/fuel ratios to the furnace, which resulted in lowering concentrations of free oxygen in the combustion products from about 3% to about 1.5%. As a follow up, bench scale experiments were carried out which involved characterizing the oxidation behaviour of low carbon steel in various gas mixtures of O2, CO2, H2O and N2, at different oxidation temperatures. Scaling rates during reheating were predicted from oxidation rates obtained in the laboratory. The work also involved in-situ characterization (using C2 Neutron Diffractometer at AECL) of the phase compositions of the iron oxides, "scale", that form on low carbon steels during oxidation at elevated temperatures. Growths in the intensities of the diffraction peaks associated with characteristic crystal planes of the various oxides (FexO, Fe3O4 and Fe2O3) were monitored on-line. The volume fractions of the oxides in the developing scale were calculated on the basis of ideal structure factors and measured relative intensities of diffraction peaks. As a conclusion of this work, it was found that rates of oxidation during reheating in the industrial reheat furnace followed a combination of linear and parabolic rate laws, with the components of the linear oxidation rates being predominant. The observed reduction in scaling rates was a result of the decrease in the free oxygen within the furnace atmosphere.
Semi-Solid Forming of Al and Mg Alloys
The
early work on semi-solid forming demonstrated the advantages of stirring an
alloy at a temperature between the liquidus and solidus in order to achieve a
homogeneous globular primary solid phase in a liquid matrix which can easily be
cast or formed in this state. The
reduced apparent viscosity of the slurry with the desired microstructure
results in fewer casting defects and improved mechanical properties. The microstructure can be retained by rapid
freezing in ingots which can then be reheated to the desired tempetaure and
extruded or injected to form component parts.
However, the introduction of this technology in the fabrication of
components for the auto industry has been slow, especially in
Recent
advances have shown that a refined semi-solid structure can also be achieved by
creating conditions that will nucleate a large number of solid phase particles
with limited dendritic growth. The
process that is the most attractive at the present time is one that can be
generally called « slurry on demand » where the alloy is cooled at a
controlled rate with enough natural mixing and without using mechanical or
electomagnetic stirring. This controlled
cooling leads to a globular primary phase and can be processed to obtain a
desired solid fraction. The most recent
of these processes is the New Rheocost Process (NRC) developped by UBE
Industries for both Al and Mg alloys and is presently being commercialized in
the
Al-Alloys
Previous
studies on hypereutectic Al-Si casting alloys and composites have been shown to
have complex rheological behavior but can be necessfully cast in the semi-solid
state under controlled conditions.
Components of A356 (Al-7Si) alloy are presently fabricated in
Another family of Al-Si alloys (hypereutectic, Al-17% Si) can also be formed using the semi-solid processing technology. These alloys also have good mechanical properties, hardness and are particularly suited for wear applications such as in cylinder liners, pistons and valve covers . The solidification structure consists of large primary Si solid crystals in a matrix of eutectic alloy. To refine the solidification structure grain refiners such as P, Sr, Na and Ni have been added to the hypereutectic composition which genarate smaller and more compact Si crystals resulting in higher tensible strength, improved elongation and facility in casting.
A rheological study of these alloy is presently in progress using Couette type and squeezing flow viscometers that have previously been used for the hypoeutectic Al-Si and Mg alloys, and composites. This work is presently carried out by Mr. Ali Reza Hekmat Ardakan as part of his M.Sc.A. program. A more comprehensive study on the forming and characterization of these alloy has been submitted as a grant proposal to the FQRNT – Actions concertees program, in collaboration with Alcan, Université du Québec a Chicoutimi, and the NRC-Aluminium Technology Centre at the UQAC campus. This proposal consists of a three year study to optimize the choice of structure modifiers and to establish processing criteria for the forming of these alloys in the semi-solid stage using a new slurry on demand process developped by Alcan called SEED where the partially solidified ingots are then injected into an industrial scale moulding machine (BUHLER) to form finished prototype parts. The work plan includes a thermodynamic evaluation of the alloy systems and rheological characterisation to be carried out at Ecole Polytechnique and at UQAC, whereas the casting trials will be carried out at the NRC-Aluminium Technology Centre. The research program also includes numerical simulation of mould filling, microstructural analysis and determination of mechanical properties.
Mg-Alloys
The determination of the rheological characteristics of Mg based alloys has been carried out by Mr Faouzi Messaoud as part of his Ph.D. program. The experimental work work consists of the measurement of the viscosities of AZ91D and some creep resistant alloys (AJ52x and AJ62x) using continuous cooling and isothermal experiments at different shear rates. Relationships of the variation of the viscosity with shear rate, solid fraction and duration of shear have been developed to characterize the rheological models taking into account the morphological evolution of the solid phase particles in the slurry. This fundamental data is essential for the establishment of forming conditions of these alloys in order to optimize the properties of the formed component.
Thixomolding Facility
Magnesium alloys are normally die cast, requiring significantly more stringent security measures in handling the liquid alloys when compared to aluminum alloys.Thixomat Inc. has developed a high speed injection moulding machine for the semi-solid forming of magnesiun alloys based on the design of plastic injection moulding machines. This patented technology yieds high quality, net shape components using a safe, simple process that can form thin wall parts to very high tolerances, with excellent dimensioal stability, low porosity, low residual stress and minimal distortion.
To produce a part, granular alloy feed (2-3 mm) is charge continuously to the machine where it is forced through a heated barrel using a screw feeder. When the alloy reaches the desired consistency(solid fraction), it is injected at high speed into a closed die to form the component and the cycle is repeated at intervals from 20 to 60 seconds depending on the size of the casting. The process advantages are high productivity, long die life, flexibility of operation, as well as being much safer and environmentally friendly than convetional sand castings. In addition, the fabrication of net shape parts requires little or no machining.
As
noted in the Director’s remarks,
The
process technology of thixomolding is already well established, particularly in
This new facility, to be inaugurated in early 2005, will be used to establish machine operation varibles for a range of alloys that can be successfully thixomolded using the Husky THX500 M70 machine.
ENERGY AND ENVIRONMENT IN METALS PROCESSING
In-Situ Thermal Analysis Technology for Aluminum Foundry Alloys Based on Heat Pipe Technology
To produce high quality castings, one must monitor such parameters as the melt quality, the grain refinement and silicon inoculation and modification during the production of the commercial casting. Thermal analysis is a tool one can use for both monitoring and providing input to the process control of the operation.
The current technique of performing
thermal analysis in commercial foundries is to pour a relatively small quantity
of the molten aluminum alloy into a sampling cup and to then acquire the
cooling curve. This approach is limited in that one has limited control of the
cooling rate and hence the solidification rate of the sample. Moreover, this
process requires a fair amount of user intervention and effort. In the past,
studies have been conducted in an attempt to develop a system for conducting
thermal analysis in-situ. In a study at
In order to improve the technique of accomplishing real-time thermal analysis with an in-situ probe, a new method that is based on McGill heat pipe technology was developed. In the new system, a controllable and flexible water based heat pipe probe is used to solidify a small quantity of metal while residing in the melt. The solidified aluminum is remelted after completing the thermal analysis. This is a key feature of the probe. It resides continuously in the melt yet it is able to both solidify a sample of the melt and then to subsequently remelt it. Various solidification rates encountered in commercial castings are attainable by adjusting the heat extraction rate of the unit.
Heat Pipe Applications
Prof. Mucciardi and his research team are concentrating their efforts on exploring, developing, and testing high temperature metallurgical applications of heat pipe technology. Introducing this technology briefly: a heat pipe consists of a sealed pipe shell, circular or otherwise, containing a heat transferring (working) substance. During heat pipe operation, heat is introduced to the pipe from the heat source. At this section of the heat pipe, the working substance evaporates. The vapor flows to the heat sink section of the heat pipe where it condenses on the pipe wall and returns to the evaporator in liquid form.
While the advantages of heat pipes have been exploited in other engineering applications, most notably the cooling of space satellites, the metallurgical industry has been slow to adopt heat pipe technology. In many ways, all pyrometallurgical operations are based on the precise, controllable, safe and inexpensive transfer of heat loads during process steps. It is surprising, therefore, that this segment of industry has done little or no research into such an innovative means of heat evacuation. Prof. Mucciardi, who holds a U.S. Patent for one application, is not only a strong proponent of this technology but a pioneer of this technology for process metallurgists.
Some notable successes of the research group are 1) the development of an oxygen, heat pipe injection lance for steelmaking and copper processing, and 2) the development of an in-situ thermal analysis probe for aluminum and its alloys. In addition, members of the group are also active in producing software capable of simulating these processes. To date, a software package capable of simulating the thermal behaviour of heat pipe injection lances has been completed and is commercially available. Several other packages are forthcoming.
Heat Pipe Probe for the Thermal Analysis of Melts
Our research group has developed a unique method for conducting thermal analysis of melts and in particular aluminum alloys. Preliminary tests have been carried out successfully and have shown that the probe can be used to conduct thermal analysis of aluminum and its alloys on a semi-continuous basis. Heat pipe technology constitutes the basis of operation of the probe. The bottom portion of the probe resides below the melt surface while the top segment protrudes above the melt. Solidification rates spanning the entire spectrum encountered in commercial castings are attainable by controlling the heat extraction capabilities of the probe. Once thermal analysis is complete, the frozen sample can be remelted in-situ and the probe readied for another test. With the full development and industrial implementation of this novel method for thermal analysis, casting operations will be able to monitor melts without physically sampling the melts. Moreover, a wide range of solidification rates are accessible with the resultant economic benefits that stem from improved quality and productivity.
Unification of Heat Pipe Design for a Wide Variety of Applications
During the last year we have reviewed our work on heat pipes and have developed a unified approach for implementing heat pipe technology in a wide variety of applications. Our research puts us at the leading end of this technology spectrum. Some potential metallurgical applications are:
1) lance for injecting
reagents such as oxygen,
2) tuyere for injecting
reagents,
3) burners,
4) generic energy extractor,
examples include
a) the cooling of casting
molds,
b) the cooling of liquids
and, in particular, liquid metals, slags, mattes, etc.
c) the cooling of hot
gases such as furnace off gases,
d) the cooling of furnace
walls and ducts
5) temperature, depth
and level sensors.
Our research on lances and casting mold, with sodium and water working substances, is conclusive. McGill’s innovative heat pipe technology is being tested by several industrial concerns such as Posco, RSR Technologies, Elkem, InterMag, Grenville Castings and Noranda. It is expected that production units based on heat pipe technology will start appering in the near future.
Heat Pipe Cooling of a Copper Block Taphole
The proximity of operators to copper tapholes in the metallurgical industry has caused a drive to seek an improved cooling mechanism vis-à-vis forced convection water cooling, which can fail catastrophically in the unlikely event of a failure.
The
purpose of this research is to develop an industrial-scale copper tapblock
using novel heat pipe technology, which is fundamentally safer than
conventionally cooled tapblocks. A tapblock cooling system incorporating two
independent heat pipes was designed at
Research in 2005 will primarily be conducted through the design and testing of a cooling system based on heat pipe technology applied to a slag launder similar to that currently used at the Hoboken blast furnace. It has been agreed upon that the design and implementation of a heat pipe-cooled slag launder (not a critical system) would be a suitable application to evaluate the long-term performance of the technology in an industrial environment, prior to the industrial testing of the heat pipe-cooled tapblock. This will allow for the validation of the modeling of the fluid mechanics within the heat pipe necessary for the prediction of the dry-out limitation.
Top-Blowing Injection Lance
Injection lances based on heat pipe technology have been designed, fabricated and studied to improve our understanding of the way they work. During the last five years, significant advances have been made. Laboratory scale lances that operate under extremely harsh thermal conditions have been successfully tested and mathematically modelled. McGill has signed an agreement with Posco to commercialize the heat pipe oxygen lance for use in steel degassing units. McGill has produced a commercial prototype which is currently being tested in plant trials in Korea. If the trial is successful, Posco will replace their conventional lances with heat pipe lances. This will represent a break through for heat pipe technology and will ultimately lead to a new generation of injection lances for such industries as steelmaking, copper smelting and lead-silver refining. The advantages for pyrometallurgical industries of these lances over conventional lances are: 1) they are environmentally friendly and energy efficient, 2) they are chemically stable which in a processing environment leads to improved productivity and enhanced product quality, and 3) they are cost effective.
Mathematical Modeling of Low-High-Low Temperature (LHL) Waste Treatment
An innovative approach for waste treatment in a three-zone reactor where a high temperature zone is located in the middle of two low temperature zones is modeled in this project. A mathematical model that is capable of simulating the entire process is being developed by Dr. R. Saade, NSERC Postdoctoral Fellow. Both the conduction of temperature and diffusion of metals are simulated. They are described by the governing heat and mass diffusion equations. The diffusion region is assumed to be homogeneous and isotropic. A sink term is included in the mass conservation equation to account for the mass loss. The governing equations are solved using an explicit one step method with Dirichlet boundary conditions at surfaces. The mathematical model has two important advantages: (1) It will help in determining the mechanism under which the encapsulation process may occur and (2) Provide a tool for the implementation of this new method in industry. One paper has been published and two submitted for publication.
Clean-Up of Contaminated Soil
This is a new project sponsored by UtiliCorp Inc., USA. Ms. Alison Taylor, a Ph.D. candidate employed by UtiliCorp, is involved in both field trials and lab experiments. The purpose of the project is to determine whether thermal remediation combined with bioremediation is effective in cleaning up soil contaminated with hydrocarbons. This project is developed together with Prof. J. Rasmussen (McGill, Biology) and Prof. A. Dufresne (McGill, Medicine).
Mathematical and Experimental Investigations of the Thermal Decomposition of Solid Waste
With respect to the thermal remediation of solid industrial wastes, the primary objective is to maximize the reduction of volume and mass of waste while at the same time minimize the operating costs. This research stems from the latter fact and aims at investigating the dynamic decomposition of solid waste during heating and its associated kinetics. This is done by performing experimental tests and complemented by the development of mathematical models. Two students, Mr. Michael Croteau and Ms. Yasmine Sarruf, and one PDF, Dr. R. Saade, are involved in this project.
PAH Release during Thermal Treatment of Waste Oil
Polycyclic Aromatic Hydrocarbons, PAHs, are byproducts of combustion processes that use waste oil as fuel. Since some of these compounds are known to be carcinogenic and mutagenic, the release of these compounds into the atmosphere should be minimized. In this project, operating parameters that are be important in reducing the emissions of PAH compounds are being determined. A combined thermogravimetric analyzer (TGA) and Fourier Transform Infrared Spectrometer (FTIR) is used. The evolution of the PAHs is monitored with the FTIR to develop evolution profiles which are necessary to describe the behavior of the compounds during the thermal treatment process. Mr. Sergio Di Lalla is in a process of finalizing his M.Eng. thesis on this subject.
Thermal Treatment of Hazardous Solid Wastes
The objective of this project is to develop a new treatment method that can encapsulate toxic metals inside ash particles during combustion of solid wastes. Such encapsulation will effectively prevent secondary pollution due to toxic metal leaching from the ash while disposed of. The experiments were conduced in a computer-controlled high-temperature thermogravimetric furnace (TGA). Results indicated that the encapsulation process depends on the residence time, and heating/cooling rates. In the case of contaminated sludge, the compact dense external shell built of light metals (Si-Al-Na-K-Ca) is able to prevent toxic metals (Cd, Cr, Pb) from leaching. Mr. Guohui Zheng, now a Ph.D. student, is involved in this research. Two journal and three conference papers have been published/presented.
TEXTURE AND PROPERTIES OF ENGINEERING MATERIALS
Investigation of Wear-Corrosion Synergism and Development of Guidelines for Materials Selection and Design
Tribocorrosion is defined as the chemical-electrochemical-mechanical process leading to a degradation of materials in sliding or rolling contacts immersed in a corrosive environment. Examples of the occurrence of tribocorrosion in field practice are the accelerated corrosion of tailing pipes and pumps for slurry transfer, the degradation of hip prosthesis and dental fillers, etc. Objectives of the proposed research are (1) to clarify the synergism of wear and corrosion and develop fundamental theory of corrosive wear (2) to develop guidelines for materials selection and design against corrosive wear under various conditions.
Effect of Rolling Conditions on Texture and Microstructure of Mg sheet AZ31
The driving force behind the development of magnesium alloys in automobile applications is the potential for more economic use of fuel and lower emissions. However, the absence of sheet magnesium from mainstream production programs at present is predominantly due to the lack of sufficient formability. The objectives of this research are: (1) to understand the deformation mechanism of magnesium, (2) to determine the effect of rolling conditions on texture and microstructure of Mg sheet, and (3) to identify processing route for optimizing formability of Mg sheet through texture control.
Investigation of wear-corrosion synergism and development of guidelines for materials selection and design
In order to attack industrial corrosive wear problems, there is a need for fundamental understanding of wear-corrosion mechanisms and development of solid guidelines for materials selection and design. Objectives of this research are:
to clarify the synergism of wear and corrosion and develop fundamental theory of corrosive wear;
to develop guidelines for materials selection and design against corrosive wear under various conditions.
Protective Coatings for Copper and Copper Alloys
Copper molds are major element in the overall economics of a continuous casting of steel, which explains the number of innovative approaches used to increase the length of time during which the mold shows acceptable dimensional stability or satisfy the new demands to be met by the mold liners. The aim of this project is to improve the thermal and mechanical properties of the copper moulds through surface treatment techniques, such as the application of coatings.
The application of titanium aluminides intermetallic compound coatings on superalloy surfaces
There is a continuing demand to increase the temperature in combustion chambers and gas turbines in order to enhance the efficiency of the plants. A reduction in density is the most important material property for achieving a better performance and density is often three to five times more effective in reducing structural weight. Among different elements, titanium offers the highest weight saving as an alloying element in aluminum for high temperature applications. Titanium aluminide represent a new class of lightweight materials that have low density with high strength up to relatively high temperature.
Growth Rate and Phase Composition of Oxide Scales during Hot Rolling of Low Carbon Steel
The rate of scale growth on low carbon steel in air over the temperature range 600-1200 °C and the phase composition changes that occur between 750-1200 °C were investigated. The phase composition of the oxide scales changed with temperature and time. For the initial 30 s of oxidation, wustite was the predominant phase in the temperature range 800-1200 °C and as oxidation proceeded, the percentages of magnetite and hematite increased. The homogeneity of the oxide decreased as the oxidation temperature increased. At 850°C, with the air velocity of 4.2 cm/s, the oxide was homogeneous, and for the first 120 s of oxidation, the oxide had a high percentage of wustite and a low percentage of hematite. This indicates that 850°C is the ideal temperature for the finishing strip mill in order to reduce work roll wear and surface defects.
Corrosion Resistant Conductive Polymer Coating for Pipeline and Structural Steels
Conductive polymer has immense commercial potential for protecting investment made in the automotive, oil and gas industries. It is inexpensive, easy to apply with service adaptable properties. Our research allows us to find the best performance conductive polymer for each application.
Study of Porous Anodic Alumina as a Template for Nanostructure Fabrication
Research consists of studying and developing porous alumina template through controlled aluminum anodization. The template will be used to create nanostructures though electrodeposition processes. This approach is promising because it offers the flexibility of using a variety of materials to be grown through electrodeposition, and it gives accurate control of the fabrication process and of the alumina template attributes and features. This unique technique shows potential in different fields such as the semiconductor and biomedical industry, where the collective properties of nanostructures and the manipulation of multiple nanostructures could lead more thorough applications in nanotechnology.
Effect of Microstructure and Texture on the Oxidation of Zr-2.5Nb Pressure Tubes
In CANDU nuclear reactors, Zr-2.5wt%Nb alloy is used as pressure tube material, and oxidation controls life time of the tube. The study is undertaken to minimize the oxidation rate by modifying the microstructure and texture of the tube. The main objective is to reveal oxide growth mechanism of the Zr-2.5Nb tube by investigating the effects of (i) stress state and texture of oxides, (ii) substrate microstructure and (iii) high temperature condition, on the oxidation behavior of the tube.
Fabricated Processes and Hydrogen Separation of Aluminum and Palladium Membranes at Elevated Temperature
Fuels cells produce electricity through the electrochemical reaction of hydrogen and oxygen. They have higher efficiencies than internal combustion engines, produce little or no emissions (depending on the source of the hydrogen), offer fuel flexibility, and generate little noise. High purity hydrogen is required for operation of proton type fuel cells. A common approach for extracting high purity hydrogen from industrial gas streams involves selective diffusion of hydrogen through a membrane. Membrane separation is regarded nowadays as a preferred method for production of purified hydrogen. Metal and ceramic membranes are relatively promising research areas closely related to materials chemistry, chemical reaction engineering such as liquid filtration, gas separation and catalysis. Although low temperature separations can be carried out by polymeric membranes, metal and ceramic membranes are promising membranes as they offer greater chemical and thermal stability and are often more selective. In this work, novel aluminum membranes related to their processes and thin palladium membranes deposited on nano nickel powders-soaked porous stainless steel substrates are developed. After nano-size Ni powders were soaked into cavities in the porous substrate, resulting in a smooth and flat surface, it is easily deposited by thin palladium membrane. Electrodeposition of aluminum membrane on porous stainless steel substrate was carried out at room temperature, so the substrate will not be subjected to high temperature attack. The membrane preparation processes and hydrogen separation mechanisms were also studied in detail.
The Effects of Texture and Microstructure on the Reliability of Copper Interconnects
The aim of this research is to improve the understanding of the influence of microstructure and texture on electroplated copper damascene interconnects which is important for the electronic metallization process. Stress distribution in Cu interconnects will be simulated in order to propose a quantitative model of texture evolution during/after damascene process. The ultimate goal of the project is to propose processing parameters to optimize texture and microstructure to obtain the defect free copper damascene interconnects.
Microstructure and Its Influence on Hydrogen Diffusion in Metallic Films
The aim of this research is to determine the role of microstructural factors, such as grain orientation distribution (Texture), grain size and grain boundary in the absorption and permeation of hydrogen in metallic materials. Hydrogen diffusion will be simulated in order to get predictive models for controlling hydrogen permeation. The ultimate goal of the project is to propose methods to improve and optimize transport of hydrogen which will be used to control the rate of hydrogen diffusion. Hydrogen absorption and diffusion are influenced by microstructure of metallic films. It is important to understand microstructural characteristics of films.
The Study on Texture and Hydrogen Ingress of Zirconium Alloy
The importance of zirconium alloys in the nuclear power industry is attributed to their high corrosion resistance. It is suggested that texture of zirconium oxide play an important role in limiting the rate of oxidation and hydrogen uptake. The objective of this research is to understand the correlation between texture and hydrogen pickup and to optimize the texture of zirconium oxide.
High Temperature Oxidation of Steels
This research is to establish the model of high temperature oxidation of steels and to suggest the condition of heat treatment for descaling. For these purposes, the in-situ method of phase analysis for textured oxides is proposed and the oxidation model for continuous heating is verified. In addition, a relationship between stress, high temperature oxidation and lattice matching between the oxide and the substrate are examined. The characteristics of descaling are correlated with the oxide adherence, the distribution of stress in oxides and distribution of voids and inclusions.
Equipment and Methods for On-Line Texture Analysis
Laboratory equipment has been designed to develop methods to be used to measure texture on-line in the production environment. Research has concentrated on refining the analysis techniques used to obtain texture information from the limited experimental data, and to predict the plastic strain ratio from the texture on line.
(OIM Image of Al Thin Film)
Equipment for Texture Measurement of Thin Films
New equipment has been built to study the texture in thin film materials. In the past year, the equipment has been installed and software has been written to automate both the data collection and analysis. The equipment will expand the texture measuring capability of McGill's Texture Laboratory into the following research areas: the study of Zinc-alloy coatings for steel; the study of oxidation layers on Ni, Ni-Cr and Inconel alloys; the study of metallization lines in semiconductor materials.
A Mechanism of Texture Formation during Electrodeposition
In this research, and explanation of the mechanism of
texture development during electrodeposition has been put forward. A series of
iron foils deposited in
different conditions were measured, and the role of the magnetic field applied
in the plane of the layer on the texture development was investigated. To explain
the mechanism of texture development and its variation with changes in the
deposition condition, a
The Texture Development in Strip-Cast Aluminum and Al-Si Ingots
The texture development and texture inhomogeneity in aluminum sheets obtained from strip-casting were studied. The texture variations through the casting thickness were examined. The casting was hot rolled, cold rolled and annealed in order to obtain sheets which could be used for deep drawability testing. The measured anisotropy of the plastic strain ratio was discussed in view of producing aluminum cans with this material. The texture of AlSi ingots, were also investigated. Textures in different zones of the ingots were measured and the mechanism of texture variation was analyzed. This work is oriented towards controlling the texture in ingot casting.
Oxidation Resistance in High Temperature Alloys
This research is focused on modifying the surface texture and applying reactive element coatings to produce materials with high oxidation resistance. The basic study, concerned with analyzing the inhibition of oxide growth mechanism was conducted on the model system Ni-NiO-CeO2. CeO coatings were also tested on alloys with complex chemical composition, such as Inconel 600 and 601.
Computer Simulation of Inter Granular Fracture of Ni3Al
Molecular dynamics (MD) and the embedded atom method (EAM) have been applied to investigate the characteristics of various grain boundaries in Cu and nil. The grain boundary energy, grain boundary structure, and intergranual fracture resistance, have been predicted using MD simulation. A two-dimensional microstructure with non-regular polygonal grains has been developed to study the influence of grain boundary on toughing and inter granular fracture in brittle materials nil. Microstructural effects are included by varying the average grain size, grain boundary energies, grain boundary distributions, grain boundary geometry distributions, inter granular fracture resistance, and surface energy. The potential for the control of structure-dependent materials has been studied on the basis of grain boundary design through the control of the grain boundary character distribution (GBCD). the research in this area is being done by J. Lu and the results have been submitted to Interface Science and/or are currently being prepared for publication.
Methods for Correlating Textures and Magnetic Properties in Electrical Steels
Fe-Si electrical steels are soft magnetic materials used for magnetic cores in electrical machines. Various new methods to analyze the influence of texture and structure on magnetic properties of steels were proposed. A new method for measurement of magnetic texture by neutron diffraction was developed. It was proposed that the Barkhousen Noise method be used to reveal the existence of characteristic field controlling the homogenization of the magnetic flux. New models linking the magnetic properties with texture and microstructure were developed.
Hydrogen Permeation and Adsorption in Metals
New equipment was built to study hydrogen ingress, adsorption and permeation. This equipment will be used to study hydrogen embrittlement in steels and stainless steels as well as hydrogen adsorption on metal surfaces, hydrogen permeation through thin layers of oxides and hydrogen permeation through thin layers of oxides and hydrogen transport in nanocrystalline alloys.
A Comprehensive Model of Recrystallization for Interstitial Free, Fe-Si Steels and Al Alloys
A Computer model of recrystallization process which incorporates both microstructure and crystallographic texture is proposed. This model is applied to the recrystallization of cold-rolled interstitial free (IF) steel. The nucleation mechanism is being implemented using the concept of subgrain coalescence. This model provides the quantitative information of a change in the volume fraction of the recrystallization, the grain size distribution and the crystallographic texture. Another model has been developed to explain the nucleation and recrystallization of alloys. New model of abnormal growth, and Goss texture development in grain oriented Fe-Si steel was proposed and tested.
PROCESSING AND CHARACTERIZATION OF POLYMERS
Effect of Isotacticity on the Simultaneous Equibiaxial Stretching of Isotactic Polypropylene Films
A laboratory film stretcher that closely simulates the stretching conditions encountered on the industrial biaxial tenter-frame stretching process was utilized to investigate the simultaneous biaxial stretching of isotactic polypropylene films in the partly molten sate. The effects of chain tacticity of the polypropylene resins on the biaxial deformation behavior and the resulting mechanical properties were studied. Correlations were found and explained between the deformation behavior, end-film properties and the morphological characteristics of the partly molten state.
Influence of Weight Fraction and Shear Rate on Particle Size in Polymer Blends
A relationship between particle size and volume fraction, viscosity ratio, interfacial tension, and shear stress was suggested, which can be used to estimate quantitatively experimental data of particle sizes in concentrated polymer blends, for simple shear flow. The relationship explains the observation that, for coalescence-suppressed polyethylene/polyamide-6 blends with high viscosity ratio (>>1), to which maleic anhydride grafted polyethylene was added as a compatibilizer, the particle sizes decreased with the increase of the dispersed phase weight fraction.
A Generalized Melting Temperature Equation of Polymers
A generalized equation is introduced to clarify conceptual definitions of copolymer melting temperatures. This treatment incorporates the effects of comonomer volume, crystal length, folding surface free energy and enthalpy of fusion, when comonomers are excluded from the crystallite lattice. Both the Gibbs-Thomson Equation for homopolymers and a modified application to copolymers have also been derived from the proposed equation as two special cases. The equation satisfactorily evaluates the melting temperatures of linear polyethylene homopolymers (including paraffins) and various a-alkene-ethylene copolymers.
Computer Simulation of the Film Blowing Process
A detailed two-dimensional simulation of the film blowing process is developed based on a mathematical model that incorporates the Phan-Thien Tanner (PTT) and Neo-Hookean constitutive equation with crystallization effects. The PTT constitutive equation is employed in the hot region, while the Neo-Hookean constitutive equation is used in the cold region to describe the rheological behaviour of the film. The model predicts bubble shape dimensions, temperature distribution, crystallinity, and orientation.
A Genetic Optimization of Shrinkage by Runner Balancing
A new approach to runner balancing is proposed which accurately characterizes the relevant issues and eliminates problems associated with the traditional approach to runner balancing. The runner diameters are varied by a multi-objective genetic algorithm, which simultaneously optimizes the product shrinkage and cost. The results suggest that balanced runner systems, which exhibit large differences in cavity pressure, have lower product costs than systems characterized by similar fill times and cavity pressures. The optimization of the secondary runner lengths also reduced costs significantly.
Synthesis and Characterization of High Density Polyethylene Clay Nanocomposites
High-density polyethylene/clay nanocomposites were prepared, using a twin-screw extruder. The nanocomposites were characterized with TEM, XRD, DSC, optical microscopy and tensile testing. The results show some exfoliation and indicate that the clay does not affect the melting temperature or crystallinity of the HDPE. However, the clay acts as nucleation agent and reduces the crystallite size. The clay improved the modulus, without causing large decrease in the elongation and impact strength.
Melt Processing of PA-66/Clay HDPE/Clay and HDPE/PA-66/Clay
Polyamide 66/clay, high-density polyethylene/clay and HDPE/PA66/Clay nanocomposites were prepared, using a twin-screw extruder. The nanocomposites were characterized with TEM, SEM, XRD, DSC, optical microscopy and tensile testing. Effects of processing conditions and clay modifier were evaluated. The results show that the incorporation of mixing and shearing elements and higher residence times in the twin screw extruder enhance exfoliation. Compatibility of the clay modifier with polymer matrix has an important role in exfoliation. Clay has not effect on the crystal forms of PA-66, it has no effect on the melting temperature and crystallinity of the PA-66 and HDPE. However, it increases marginally crystallization temperature and acts as a nucleation agent and reduces the crystallite size. Clay in the blend nanocomposites acts as a compatibilizer and it changes the morphology. TEM micrographs suggest the presence of exfoliation structure in PA-66 and intercalated structure in HDPE.
Estimation of Stress for Separation of Platelets by Melt Processing
A theoretical model is proposed to describe the exfoliation process of clays in polymer melt flows. It shows that exfoliation is a function of shear rate, viscosity of the matrix, the Hamaker constant, and geometrical variables. For simple shear flow, the effects of the variables on the exfoliation of two clay platelets were estimated by obtaining the stress ratios: (stretching stress/van der Waals’ stress). The stress ratios are significantly dependent on the orientation of the connector vector. For overlapped fraction equal to 1, the magnitudes of the stretching stress ratios increase with an increase of the shear stress level and the gallery spacing. They decrease with an increase of the aspect ratio of the platelets and the Hamaker constant. For overlapped fractions less than 1, the magnitudes of stress ratios increase with an increase of the shear stress level while they increase with a decrease of the Hamaker constant. They show a minimum as the overlapped fraction and the aspect ratio increase. For gallery spacing, they increase or show a maximum with gallery spacing depending on given conditions. Tactoids with more clay layers can be broken more easily. The predictions of the model appear to be in harmony with experimental observations reported in the literature.
Measurement and Prediction of Temperature Distribution in an Injection Molding Cavity
A method to measure the melt temperature distribution in an injection mold cavity is developed. A thermocouple is used in the construction of a sensor with a tip that can be adjusted at different depths of a mold cavity, to measure temperature profiles at different positions in the mold. Polymer temperature distributions are measured and factors affecting temperatures and the key variables that influence distributions are determined. Measurements are compared with temperatures obtained from numerical simulation of the injection molding process using a three-dimensional heat transfer analysis. Although showing lower values and generally higher cooling rates, temperature data measured from the mold cavity indicate similar behavior to predicted transient temperature distributions.
Residual Thermal Stresses in Injection Moldings of Thermoplastics: A Theoretical and Experimental Study
Internal stresses in injection molded components, a principal cause of shrinkage and warpage, are predicted using a three-dimensional numerical simulation of the residual stress development in moldings of polystyrene and high-density polyethylene. These residual stresses are mainly frozen-in thermal stresses due to inhomogeneous cooling, when surface layers stiffen sooner than the core region as in free quenching. Additional factors in injection molding are the effects of melt pressure history and mechanical restraints of the mold. Transient temperature and pressure fields from simulation of the injection molding cycle are used for calculating the developing normal stress distributions. Theoretical predictions are compared with measurements performed on injection molded flat plates using the layer removal method on rectangular specimens. The thermal stress development in the thin-walled moldings is analyzed using models that assume linear thermo-elastic, and linear thermo-viscoelastic compressible behavior of the polymeric materials. Stresses are obtained implicitly using displacement formulations, and the governing equations are solved numerically using a finite element method. Results show that residual stress behavior can be represented reasonably well for both polystyrene and high-density polyethylene materials. Similarities in behavior between theory and experiment indicate that both material models provide satisfactory results, but the best predictions of large stresses developed at the wall surface are obtained with the thermo-viscoelastic analysis.
