Current Research Projects 2002
- 3-D Modelling and Computer Simulation of the Rotating Impeller Particle Floation Process
- An Energy Savings Model for Heat Treatment of Casting
- De-Lubrication during Sintering of P/M Parts
- Electrospinning of Biopolymers
- Characterization of Thermal Barrier Coatings Deposited by Electron Beam-Physical Vapor Depositon
- Evolution of the Eutectic Microstructure during Solidification of Hypoeutectic Al-Si Alloys
- High Strength Diffusion Bonding of Sapphire
- Initial Microstructural Analysis of A36 Structural Steel from WTC Building 7
- Low Cost and Energy Efficient Methods for the Manufacture of Semi-Solid (SSM) Feedstock
- Modeling of an Aerospace Sand Casting Process
- Operating Mechanisms During Dynamic Loading of AL Cast Components
- Optimization of Heat Treatment Using Fluidized Bed Reactors
- Part Load Design and Temperature Analysis within Loaded Furnace
- Process Based Cost Analysis for Solid Oxide Fuel Cells for APUs
- Quenching-Understanding, Controlling and Optimizing the Process
- Reliability Testing of Polysilicone in MEMS
Modeling of an Aerospace Sand Casting Process
Advisors:
D. Apelian
Students:
J. Ziolkowski
Description
Theoretical issues relating to the aerospace sand casting simulation are laid out. A sensitivity analysis is performed to examine some key influential parameters through doing simulations on thin walled castings. A verification exercise is done to match simulation with reality utilizing the information gained in the sensitivity analysis. Validation on a real production casting is performed using the tuned parameters from the verification exercise.High Strength Diffusion Bonding of Sapphire
Advisors:
R.N. Katz
Students:
Daniel Fiore
Description
New high performance optical systems which require highly durable, broadband window materials demand larger window sizes than those currently available. To meet this need, a low cost edge-bonding process was previously developed for producing large area sapphire windows from smaller, melt-grown blanks. The method uses a polycrystalline alumina interlayer to promote diffusion and single crystal conversion at the interface between two sapphire substrates and produce high strength bonds. The goal of the current research effort is to determine the optimal alumina composition for maximum bond strength.
Polycrystalline alumina fillets containing various chemical additives were prepared by tape casting for use in bonding trials. Oriented sapphire blanks were edge bonded in a specialty furnace which accurately aligns and applies a load to the components during heat treatment. This approach is consistent with and builds upon the methods used in previous edge-bonding studies. The flexure strength of the bonded samples, as compared to monolithic sapphire, was used as the performance metric. Additional bonding runs were carried out using the highest performing fillet composition in order to provide a sufficient number of specimens to conduct a Weibull analysis of the failure probability of the bonded material as a function of applied stress.
A high purity alumina composition containing 3 wt.% SiO2, 0.05 wt.% MgO, and 0.05 wt.% Ti, produced the highest strength bonds. This composition yielded an average fracture strength of 255 MPa (37 kpsi), a Weibull modulus of 8.2, and a characteristic strength of 269 MPa (39 kpsi). These results compare favorably to monolithic sapphire specimens which yielded an average fracture strength of 284 MPa (41 kpsi).
3-D Modelling and Computer Simulation of the Rotating Impeller Particle Floation Process
Advisors:
M. Makhlouf
Students:
V. Warke
Description
Melt cleanliness is an extremely important issue in today's industry because of the ever-increasing demand for high quality cast products particularly in the aerospace and automotive industries.
Removal of solid inclusions from molten metal by floatation is one of the most commonly used melt treatment method. It mainly includes purging gas through a rotary impeller that disperses the gas in form of bubbles throughout the melt. This device is called a Rotary Degasser. In order to optimize the operation of the rotary degasser, it is important to understand the basic mechanism behind the process. Impeller rotation creates turbulence inside the melt which causes randomly distributed solid inclusions to agglomerate and form large clusters. These clusters then float up or settle down depending on their relative densities with respect to melt and thereby are removed from the melt. Agglomeration may also occur due to velocity differences between various particle sizes. In addition, inclusions attach to rising gas bubbles and are carried to the top slag.
In this study, development of a 3-Dimensional model for the process that will depict the real situation is important. Complete understanding of multiphase fluid flow in necessary. A mathematical model that's simulates the process is under development. The model can be used to predict the efficiency of degassing process by changing different process parameters.
An Energy Savings Model for Heat Treatment of Casting
Advisors:
Y. Rong, R.D. Sisson, Jr., Dr. J. Kang
Students:
Y. Bai, M. Fontecchio
Description:
The solidification of most commercial alloys involves significant volume contraction. In long freezing range alloys, melt must be fed through a partially solidified, coherent dendritic network, if porosity and surface defects in the casting are to be avoided. Commercially pure metals, influenced by a temperature gradient ahead of the interface, solidify as a plane front or a short columnar zone. In this case, melt can easily feed the solidification shrinkage. However, as alloying elements are added, the freezing range increases and dendritic solidification begins to occur throughout a large portion of the casting. During the initial period of mold filling, the dendritic network remains incomplete and the melt flows with the bulk properties of a liquid. As solidification progresses, the melt flows with the properties of a suspension of growing particles (equiaxed dendrites plus any other primary phases) in a liquid. Feedability becomes important once the semi-rigid network of the dendritic grains has formed. The dendrite arms continue to coarsen through various ripening mechanisms, and the interdendritic regions decrease in size as the volume fraction of solid increases. Channels between the dendrites and grains continue to narrow, creating an increasingly tortuous path through which the remaining liquid must flow. These narrowing fluid paths may become blocked by suspensions of non-metallic inclusions or growing intermetallic particles within the melt stream. This in turn tends to make fluid flow even more difficult. Flow eventually ceases through the narrowing channels. It is during these latter stages of restricted interdendritic fluid flow that the effect of alloy composition on viscosity and surface tension become most evident.
The main objective of this project is to investigate the effect of alloying elements that are common in aluminum-silicon casting alloys on the feeding characteristics of these alloys.
De-Lubrication During Sintering of P/M Parts
Advisors:
D. Apelian
Students:
D. Saha
Description:
De-lubrication is the first stage in a sintering operation, where the lubricants (higher weight hydrocarbons) are removed from the parts by controlled heating. Improper de-lubrication leads to defects such as blistering, sooting, micro-porosity etc in a sintered part. Most of these problems arise, as there exists a gap in the present understanding of de-lubrication. The primary motive of this work was to direct research towards the development of sensors and controls and thus, mitigate thevarious problems due to improper de-lubrication. Currently, there exists a myriad of lubricants being used during the process of compaction.
They include metallic based lubricants, polymers and non-metallic lubricants. Research was limited in understanding the de-lubrication of EBS (Ethylene Bisstearimide), as, it the most commonly used lubricant in the industry. It has replaced commonly used lubricant due to cleaner burnouts, absence of metallic residue and, cost effectiveness. The entire work was divided into three phases:
- Phase 1: Ascertain the most important parameters that affect the kinetics of de-lubrication.
- Phase 2: Investigate the type of gases released during the decomposition of EBS.
- Phase 3: Recommend a control strategy.
TGA (Thermo-gravimetric analysis) was used in phase I, the results clearly show that the rate of heating is the most important parameter during de-lubrication. Identification of gases was performed using the FTIR (Fourier transform infrared spectroscopy) and DUV (Deep ultraviolet spectroscopy). This constituted the second phase of our experiments.
The primary gases identified were carbon dioxide and a hydrocarbon (possibly hepta-decane). A reaction mechanism has been proposed for the decomposition of EBS in the presence of moisture. Finally, an empirical model for de-lubrication has been proposed in Phase III and the model was validated in an industrial furnace. Excellent correlation exists between the proposed empirical model and the experiments performed in Phase II.
This study lays down the following guidelines for the development of future sensors and controls:
- The development of future sensors should focus on the detection of CO2 and hepta-decane.
- Rate of heating determines how fast or slow the lubricant decomposes and finally escapes from the compacted part.
The empirical model may be used, as a means to determine the time a part should reside in a sintering furnace for complete lubricant burnout at a given heating rate. The empirical model has been extended to lubricants which include, Polywax, Kenolube and Zinc Stearate.
Electrospinning of Biopolymers
Advisors:
S. Shivkuma
Students:
Chen Ming Hsu and Jing Tao
Description:
Electrospinning is a fiber spinning technique that produces polymer fibers on nanometer to micrometer size in diameters. In this process, a polymer solution or melt is placed in a container that has a millimeter size nozzle and is subjected to electric field of several kilovolts. Under this condition, a polymer fiber whose diameter is reduced significantly is ejected from the nozzle and deposited on the metal screen.
Such thin fibers provide very high surface area to volume ratios and are of interest for many applications ranging from textile to composite reinforcement, sensors, membrane technology, biomaterials, and tissue engineering.
Characterization of Thermal Barrier Coatings Deposited by Electron Beam-Physical Vapor Deposition
Advisors:
R. D. Sisson, Jr.
Students:
J. Bernier
Description:
Thermal barrier coatings (TBCs) of ZrO2-7wt% Y2O3 were deposited by electron beam physical vapor deposition(EB-PVD) on stationary flat plates and cylindrical surfaces in order to understand crystallographic texture, microstructure, and deposition rate. The crystallographic texture of EB-PVD TBCs deposited on stationary flat surfaces has been experimentally determined by comparing pole figure analysis data with actual column growth angle data. It was found that the TBC coating deposited directly above an ingot exhibits <220> single crystal type crystallographic texture. Coatings deposited inside the central zone exhibited a <311>-type single crystal texture. For coatings deposited outside the central coating zone either a <111> fiber texture or a <311> single crystal type texture existed. The crystallographic texture of EB-PVD TBCs deposited on cylindrical surfaces was characterized using x-ray diffraction (XRD) at different angular positions on the cylinder substrate. XRD results revealed that crystallographic texture changes with angular position and that <220> single crystal texture was found for coatings deposited closet to and directly above an ingot. Therefore the <220> single type texture exists directly above an ingot in both geometrical cases.
Morphology differences existed between cylindrical and flat plate surfaces. Flat surfaces exhibited a dense columnar structure independent of chamber position, in which the columns grew towards the closet vapor source. Cylindrical surfaces revealed a columnar structure in which columns grew towards the closet vapor but density decrease as position changed from the bottom of the cylinder.
The coating thickness profiles for EB-PVD TBCs deposited on stationary cylinders have been experimentally measured and theoretically modeled using Knudsen's cosine law of emissions. A comparison of the experimental results with the model reveals that the model needs to be modified to account for the sticking coefficient as well as a ricochet factor. These results are also discussed in terms of the effects of substrate temperature on the sticking coefficient, the ricochet factor, and coating density.
Evolution of the Eutectic Microstructure during Solidification of Hypoeutectic Al-Si Alloys
Advisors:
M. Makhlouf, S. Shankar
Students:
H. Guthy
Description:
Foundry alloys are usually alloyed close to the eutectic compositions due to the small freezing range, good castability and desirable properties obtained. The most important aluminum foundry alloys are based on the Al-Si system, especially the hypoeutectic alloys with compositions usually ranging from 7 to 11 wt. % silicon. Solidification of these Al-Si alloys is characterized by four events: A short nucleation event, followed by growth of the dendrites until they impinge on one another, growth and coarsening of dendrite arms, and finally eutectic precipitation. Though the initial steps are fairly well understood, the precipitation of the eutectic has not been well studied. In the hypoeutectic Al-Si alloys, the eutectic precipitates at the end after the formation of primary dendrites. Thus the eutectic can nucleate either on the primary dendrites, within the interdendritic liquid by heterogeneous nucleants, or on the mold walls.
The main objective of this research project is to understand the mechanism and the sequence of events that lead to the formation of the eutectic microstructure in aluminum silicon hypoeutectic casting alloys. Understanding the mechanism of eutectic formation is essential to analyzing resistance to melt flow. Melt flow influences feeding efficiency, which, in turn influences shrinkage, porosity formation, and segregation.
Initial Microstructural Analysis of A36 Structural Steel from WTC Building 7
Advisors:
J. Barnett, R. Biederman, and R.D.Sisson, Jr.
Students:
J. Bernier and M. Fontecchio
Description:
Please look at An Initial Microstructural Analysis of A36 Steel from WTC Building 7 (Linked with permission from Minerals, Metals & Materials Society) for information regarding this project.
Low Cost and Energy Efficient Methods for the Manufacture of Semi-Solid (SSM) Feedstock
Advisors:
A. Alexandrou, D. Apelian, A.M. de Figueredo, M. Makhlouf, and Q.Y. Pan
Students:
M. Findon
Description:
This research aims to develop and evaluate low cost, energy-efficient methods for the production of high-quality semi-solid metal (SSM) feedstock. The methods will be based on grain refining processes and developed as alternatives to production routes currently in practice or under development, e.g. those relying on magneto-hydrodynamically stirred billets (MHD) or "slurry-on-demand". The MHD and the slurry-on-demand approaches require expensive additional processing and melting of alloy stock, respectively, to produce either rheocast feedstock billets for shipment to SSM casting plants or SSM slurries in-house. These unnecessary, intermediate processing steps are expensive, demand more energy, are less consistent, and are thus obstacles to the growth of the SSM technology.
The principal goal of the project is to develop and apply efficient grain refining methods to produce SSM billets with consistent characteristics at significantly lower cost premium relative to methods currently in use (e.g., MHD stirring or slurry-on-demand). The second goal of this research is to perform computational and modeling studies of the fluid flow behavior of SSM slurries. Though much progress has been made at the ACRC on this topic, issues with respect to control of instabilities and the development of case studies remain to be performed. A third goal of this research is to establish methods and procedures to demonstrate and accurately quantify the energy and total cost savings realized with the adoption of simpler methods for SSM billet production compared to current methods.
Microstructure Evolution in Magnesium Cast Alloys
Advisors:
M.Makhlouf
Students:
Yancy Riddle
Description:
The goal of this project is to characterize the solidification paths and the as-cast microstructures of commercial magnesium foundry alloys.
A combination of microstructure and cooling curve analyses will be used to establish the various reaction temperatures and the phases involved in the solidification of magnesium foundry alloys. Moreover, quenched samples will be examined at various stages during their solidification in order to completely characterize the evolution of microstructure and to study specific solidification events in magnesium foundry alloys. Dendrite coherency, and other casting characteristics of magnesium cast alloys will be carried out. This research should result in a compilation of data that will be a valuable guide for users of magnesium foundry alloys as well as alloy designers.
Operating Mechanisms During Dynamic Load of AL Cast Components
Advisors:
D. Apelian
Students:
D. Lados
Description:
With the increasing use of aluminum casting alloys in automotive applications that involve cyclic loading, fatigue properties of aluminum castings have become of great interest. During the initial stage of the fatigue project, the effects of the casting defects and microstructural constituents upon the fatigue behavior of A356/357 aluminum cast alloys were studied in great detail. In December of 1999, the first stage was completed and the final report was presented at the ACRC-May 2000 meeting. Because of the importance of the subject within the industry, as well as the need for a fundamental understanding of fatigue in cast aluminum alloys, it was decided to extend the work to the next level, to establish operating mechanisms during dynamic loading and failure.
The motivation for the second stage of the fatigue project is to design Al-SI-Mg alloys with enhanced fatigue properties based on an understanding of the mechanism of failure, and the effects of alloy compositions (i.e. major constituents present in the alloys microstructure), and applied tempers. In order to reach this target three key objectives were established.
Optimization of Heat Treatmeant Using Fluidized Bed Reactors
Advisors:
Y. M. Makhlouf and Diran Apelian
Students:
Sujoy Krishna Chaudhury
Description:
Fortunately, the metallurgy of aluminum casting alloys offers a wide range of opportunities for using thermal treatment practices to obtain desirable combinations of mechanical and physical properties. Through properly selected heat treatment regiments, it is possible to achieve an impressive array of features that are largely responsible for the current use of aluminum alloy castings in virtually every application. A typical heat treatment regimen for a typical aluminum casting alloy is comprised of a solutionizing step, followed by quenching in water and an aging step. Together, these three steps may last for over ten hours and contribute a substantial increment to the part's cost. Fluidized beds offer a more efficient means of energy transfer than conventional heat treatment methods that rely solely on convection, and thus they present an attractive alternative to traditional heat treatment. Fluidized beds achieve very rapid heat treatment for three main reasons:
- Each component enters individually into the sand medium rather than stacked among many in a basket. This allows each component to experience the maximum heat transfer rate and a precise thermal profile that is identical to that of the other parts.
- Fluidized bed heat transfer rate is superior to that of traditional hot air heat transfer.
- Fluidized beds hold a precise, even temperature throughout the heating medium, which ensures that all aspects of a component are quickly and uniformly heated, thus reducing component distortion and residual stress.
Part Load Design and Temperature Analysis within Loaded Furnace
Advisors:
Y. Rong and Dr. Quansheng Lu
Students:
Ranjeet Vader
Description:
Heat treatment is a manufacturing process to control the mechanical properties of metallic components. Part loading is an important step in the heat treatment process. The thermal exposure a component undergoes depends on the design of the furnace load, location of the component within the load, furnace configuration, thermal schedule, and control strategy. The manner in which components are loaded in a furnace makes a difference in the temperature distribution of the furnace and thus, it is a critical step.
The relationship between furnace loading and part thermal history is a complex problem. The objective of the proposed project is to develop an analytical tool to guide part load design and improve furnace temperature control. This will be based on furnace temperature distribution analysis with part load, and optimal control of part loading temperature within a loaded furnace.
Specific research tasks are: develop a CAD tool for part load design using knowledge based rules; evaluate the design based on heat transfer analysis and temperature distribution estimation; redesign the part load for improvement by comparing alternative designs; and develop a feed-forward control strategy for optimizing the thermal control.
The project is designed as a two-year project. At the end of the first year, a graphic load design tool and a heat transfer analysis system will be developed. At the end of the second year, a comprehensive system for optimal load design and temperature control system will be delivered.
Process Based Cost Analysis for Solid Oxide Fuel Cells for APUs
Advisors:
I. Bar-On
Students:
H. Woodward
Description:
Description to come
Quenching-Understanding, Controlling and Optimizing the Process
Advisors:
R.D. Sisson, Jr., M. Maniruzzaman
Students:
S. Ma, C. McGee, J. McHugh
Description:
Each year millions of dollars are lost as a result of distortion, cracking and mechanical property variations due to unexpected problems in the quenching process. A thorough understanding of the variations in quenching fluid's performance as a function of the medium's physical properties, system variables and part orientation is not currently available. This understanding will allow the development of improved and controllable quenching fluids and systems, as well as predictive models for the metal's response to the quenching process.
The project objectives are:
- Develop an understanding of the performance of quenching fluids as a function of the fluid's physical properties (i.e. viscosity, flash point, heat capacity, thermal diffusivity and boiling point) and part geometry.
- Benchmark and test the currently available quenching probes and develop a quenching media characterization system that will provide heat transfer coefficient data as a function of metal surface temperature, fluid temperature, agitation, metal surface finish and part orientation.
- Evaluate the currently available computational fluid dynamics software for their ability to predict the performance of quenching fluids.Develop user friendly software to predict the microstructures of selected steels during quenching as a function of steel composition and quenching fluid performance. The boundary conditions for this software will come from the database developed above.
- Work closely with IIT to provide data that will be needed as the boundary conditions for their models to predict distortion.
Reliability Testing of Polysilicone in MEMS
Advisors:
I. Bar-On
Students:
J. Sledziewski
Description:
Description to come
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