Date: Tuesday, Feb 10th
Presenter: Dr. Yifeng Liao, Northwestern University and the Energy Division of Argonne National Laboratory
Metallic materials have been extensively used in a broad range of structural applications ranging from orthopedic implants to gas turbine. Materials degradation under harsh environments is critically associated with local micro/nano-structure. I will first discuss the structure and wear of CoCrMo alloy used for orthopedic devices. Metal hip replacements made out of CoCrMo alloy are extensively used in the United States, but the use of this type of device experienced a sharp decline in the past few years due to issues related to wear and corrosion. We examined retrieved metal hip replacements and discovered a new nano-phase that may be detrimental. Using in-situ wear tests in a transmission electron microscope, we observed unprecedented details of constituent phases wear in real time. I will also address the anomalous yield behavior of Fe2MnAl intermetallic alloy. The yield strength of Fe2MnAl single crystals increases from 170 MPa at room-temperature to 300 MPa at 700 K, a property desired in high temperature applications. We deformed Fe2MnAl single crystals using in-situ tensile straining, and observed superdislocations dissociation into individual partial dislocations at elevated temperatures. These partial dislocations glided in the ordered matrix, resulting in an increase in the strength.
Dr. Yifeng Liao is a Research Assistant Professor in the Department of Materials Science and Engineering at Northwestern University, and jointly appointed at the Energy Division of Argonne National Laboratory. He received B.S. and M.S degrees in physics at Sun Yat-sun University, China, and PhD degree in materials science at Dartmouth College, NH. After graduation, he worked as a postdoc at Northwestern University from 2010 to 2012, and has been a Research Assistant Professor since 2012. His research focuses on physical/mechanical metallurgy, transmission electron microscopy, orthopedic materials, and tribology.