Mechanical Engineering Department
Materials Science & Engineering

Seminars 2002

Progress on Numerical Simulation of Casting Processes

Monday, November 25th, 2002, 11:00 AM, Washburn 323

Presented by Professor Baicheng Liu
Department of Mechanical Engineering
Tsinghua University
Beijing, China

The presentation focused on the modeling and numerical simulation of solidification process of ferrous and non-ferrous castings, including, heat transfer, microstructure and fluid flow in mold filling. Prediction of defects such as shrinkage, deformation and hot cracking will be also addressed.

Professor Baicheng Liu has been with the Department of Mechanical Engineering, Tsinghua University, Beijing, China since he graduate in 1955 with a Gold Medal. He is an academician of the Chinese Academy of Engineering. As a Visiting Scholar, he worked in University of Wisconsin-Madison and Massachusetts Institute of Technology from 1978 to 1981. His major research interests and expertise are fundamental study and modeling of aluminum and magnesium alloys net shape casting, and physical metallurgy of cast alloys as well. His research has been recognized worldwide. He is now in charge of several national research projects on Macro and Micro Modeling of Casting and Solidification Processes of Aluminum and Magnesium Alloys funded by the State Ministry of Science and Technology, the National Natural Science Foundation of China, etc.

Prof. Liu has fulfilled 20 research projects and holds two patents. He won many awards from the Chinese government for teaching and research, as well as, two awards from the United States. He has published more than 260 papers. He has visited more than 20 universities in different countries around the world where he has given seminars. He presented more than 20 papers and several keynote speeches at different international conferences. He is also the editor of "International Journal of Cast Metal Research".

Deposition Rates on EB-PVD TBC's on Cylindrical Surfaces

Thursday, January 24th, 2002 9:00AM Washburn 323
Presented by J.S Bernier, W.C.S Weir, R.D. Sisson, Jr.

The coating thickness profiles for EB-PVD TBC's deposited on stationary cylinders have been experimentally measured and theoreticaly modeled using Knudsen's cosine law. A comparison of the experimental results with the model revealed that the model needs to be modified to account for the sticking coefficient and a ricochet factor. These Results are discussed in terms of the effects of substrate temperature and coating density. The results for cylinders are also compared with our result for flat plates.

Microstructural Evolution of EB-PVD TBC's on Cylindrical Surfaces

Thursday, January 24th, 2002 9:00AM Washburn 323
Presented by R.D. Sisson, Jr., Md. Maniruzzaman, J.S. Bernier

The microstructures of EB-PVD TBC's have been characterized as a function of angular position on cylindrical surfaces as well as position in the coating chamber. The microstructures were characterized using x-ray diffraction for crystallographic texture analysis as well as optical microscopy and scanning electron microscopy for density determination as well as crystal growth morphology. The results revealed several very strong crystallographic textures as well as systematic density variations around the cylinder.

Quantitative Microstructure Characterization of Semi-Solid Alloys

Thursday, January 31st, 2002 9:00AM Washburn 323
Guest Speaker: Qingyue Pan; Postdoctoral Fellow, WPI Metal Processing Institute

The rheological properties of semi-solid metal slurries are strongly dependent on their microstructure. Specifically, three characteristic microstructural parameters are critical in determining rheological behavior and flow properties of aluminum semi-solid slurries.

These characteristics are;

  1. The particle size of the Alpha phase.
  2. The shape factor of the Alpha particles.
  3. The entrapped liquid content within the Alpha particles.

In this project, extensive image analysis is being performed to determine evolution of the three parameters as a function of commercial processing conditions and material genealogy. Semi-solid materials being evaluated include MHD, GR, SIMA, new MIT, and UBE processed billets, and processing conditions investigated include different processing temperatures during continuous heating, as well as isothermal holding for different time at commercial forming temperatures. In addition, detailed investigations are being carried out to reveal the formation mechanism of the entrapped liquid within the Alpha phase.

The aim of this project is to establish a comprehensive knowledge base in understanding the effect of processing conditions and material genealogy on the microstructure evolution and rheological properties of various semi-solid metal slurries. Quantitative data will be provided to optimize industrial practice.

Quenching, Understanding, Controlling and Optimizing the Process

Thursday, Febuary 7th, 2002 9:00AM Washburn 323
Guest Speakers: Dr. Md. Maniruzzamna, Ms. Shuhui Ma

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.

A project in Center for Heat Treating Excellence (CHTE) was initiated in January 2000 to address these issues. The objectives of this project are:

  1. Develop a new CHTE quenching media characterization system.
  2. Develop a database for heat transfer coefficients for steels and aluminum alloys in a wide variety of quenching fluids.
  3. Develop an understanding of the performance of quenching fluids as a function of the fluid's physical properties and part geometry.
  4. Benchmark and test the currently available quenching probes.

To meet these objectives a team of faculty, post doctoral fellows, graduate students and undergraduate students has been assembled. A CHTE quench probe system has been designed, fabric from the CHTE probe system can be used to experimentally determine heatated and tested. The results from the CHTE probe system can be used to experimentally determine heat transfer coefficients for the steel being quenched that can be used to predict microstructures and distortion. A database has been designed and is being tested to record and make readily available the important data for each quenching probe system tested. This database includes not only the experimental results from the CHTE or other probe system but also the data that characterizes the quenching fluid. The database for quenching is used for quenching fluid identification, storage of experimental parameters, quenching fluid performance and quenching fluids experimental parameters.

Hazardous Waste Management and Laboratory Safety Training

Thursday, Febuary 14th, 2002 9:00AM Washburn 323
Guest Speaker: David Messier: Manager, Environment & Occupational Safety

This seminar will focus on understanding the importance of basic laboratory safety and the fundamentals of hazardous waste management. Topics to be covered include an overview of responsibilities, both for the lab worker and WPI, chemical storage practices, engineering controls, personal protective equipment and emergency response procedures.

Evolution of the Eutectic Microstructure in Aluminum-Silicon Casting Alloys

Thursday, March 21, 2002 9:00 AM Washburn 323
Guest Speaker: Dr. Sumanth Shankar

Foundry alloys are usually alloyed close to the eutectic composition 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 hypo-eutectic alloys with compositions 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 is not well understood. In the hypo-eutectic Al-Si alloys, the eutectic precipitates at the end of the solidification "journey", after the primary dendrites have been formed. Thus the eutectic can nucleate either on the primary dendrites, within the inter-dendritic 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 hypo-eutectic 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.

Computer Simulation and Database Needs for Energy Savings, Zero Environment Impact and Quality Improvements in the Heat Treating Industry

Thursday, March 28, 2002 9:00 AM Washburn 323
Guest Speaker: Prof. Richard D. Sisson, Jr.

Research Needs
Quenching Technology
- Models for heat transfer behavior in quench baths that will ensure uniform cooling of a range of loads

Process Modeling
-microstructure response models based on alloy composition, atmosphere, temperature, and time
-models to predict distortion and residual stress profiles
-database of thermal and mechanical properties up to and including heat treatment temperatures
-models for continuous cooling transformations (CCT) of heat treatable alloys
-models for continuous heating transformations (CHT) of heat treatable alloys

Software Packages
-predictive software that heat treaters can use to compare and select furnace equipment from different suppliers (a standard method of predicting furnace variability is incorporated)

General Needs for Roadmap
Heat Treating Processes that allow a shorter cycle time and require lower cost equipment. Alternative quenching media that are more environmentally friendly, and that transfer heat more efficiently. Improved process sensors, including those for carbon content, residual stress, and cleanliness. Also, more advanced controls that fully exploit there and other sensors. Enhanced computer modeling of processes, which include composition, distortion, resultant microstructures, and final properties. More effective dissemination of solutions to specific problems.

Databases for heat treating
Databases
-Heat Transfer and Quenching performance database -

-Phase diagrams for selected alloys -Diffusivities versus composition and temperature -Properties versus microstructure (i.e. porosity, Si particle size, undissolved ? and grain size)

Gas Quenching of 4140 and 304 Steels in Argon, Helium and Air

Thursday, April 4, 2002 9:00 AM Washburn 323
Guest Speakers: Celine McGee and Jaclyn McHugh

The CHTE quench probe system was modified to test the quenching performance of a variety of gases at atmospheric pressure. The tests were performed with Argon, Helium, and air at varying gas velocities. The quench probe materials used in this study were 304 stainless steel and 4140 steel. The heat transfer coefficients were calculated using the Newtonian cooling analyses. The experimental results showed that Helium produced the largest heat transfer coefficients, followed by air and Argon. The data showed a dip in the cooling rate and, therefore, heat transfer coefficient vs. temperature curve for the 4140 steel but not for 304. This dip was explained as being due to heat that is released as Austenite transformed to Bainite in this temperature range.

Nanometer Diameter Fibers of Polymer, produced by Electrospinning

Thursday, April 11, 2002 9:00 AM Washburn 323
Guest Speakers: Chen-Ming Hsu and Jing Tao

Electrospinning uses electrical force to produce the fibers, which have the nanometer-scale diameters. Electrospinning occurs when the electrical forces at the surface of polymer solution or melt overcome the surface tension and cause the electrically charged jet to be ejected. As the jet travels in the air, the solvent evaporates, an electrical charged fibers remains. This charged fiber can be electrically directed or accelerated by electrical force and then collected on the metal screen.

Highly Recrystallization Resistant Al Alloys Employing Sc and Zr

Thursday, April 18, 2002 9:00 AM Washburn 323
Guest Speaker: Yancy W. Riddle

For the past six years my research has sought to employ and understand how new dispersoid phases interact with microstructure while preventing recrystallization of wrought Al alloys. The strength of many wrought Al alloys depends, at least partially, on maintaining strained un-recrystallized microstructure created during deformation processing. However high temperature processes provide a thermodynamic driving force for boundary motion and dislocation annihilation threatening the alloy's strength. The Al3Zr dispersoid is the most potent dispersoid phase in commercial use. However this work shows that Al3Sc and more importantly Al3(Sc,Zr) dispersoids provide a major improvement to recrystallization resistance through increases in volume fraction and nucleation kinetics, reduction of coarsening kinetics, and more homogeneous spatial distribution. In some cases recrystallization is resisted up to the solidus temperature of the alloy and large deformations often retain unrecrystallized microstructure during post-forming high temperature processes.

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Last modified: October 12, 2006 14:54:34