Woodruff School of Mechanical Engineering
Development of Interfacial Phase Diagrams to Help Deciphering the Materials Genome
Dr. Jian Luo
University of California, San Diego
Monday, August 28, 2017 at 11:10:00 AM
MRDC Building, Room 4211
A piece of ice melts at zero degrees celsius, but a nanometer-thick surface layer of the ice can melt at tens of degrees below zero. This phenomenon, known as “premelting,” was first recognized by the physicist Michael Faraday. Materials scientists have discovered that interfaces in engineered materials can exhibit more complex phase-like behaviors at high temperatures, which can affect the fabrication and properties of a broad range of metallic alloys and ceramic materials. Specifically, recent studies of 2-D grain-boundary (GB) phases (also called “complexions”) shed light on several long-standing mysteries in materials science, including the origins and atomic-level mechanisms of activated sintering and liquid metal embrittlement. Recently, we have also successfully stabilized nanocrystalline alloys (with grain sizes < ~100 nm) at high temperatures (>1000C) using high-entropy GB complexions. Since bulk phase diagrams are one of the most useful tools for materials design, it is conceived that interfacial “phase” diagrams can be developed as a useful materials science tool. If time permits, I will also very briefly discuss our other on-going studies on (a) utilizing spontaneously-formed 2-D surface phases to improve the performance of various functional materials for energy-related applications, including batteries, supercapacitors, photocatalysts, and oxygen-ion conductors; (b) understanding the mechanisms of flash sintering, where we have developed a model to predict the onset flash temperature with a precision of < +6 degrees celsius, and successfully flashed ZnO (Tm = 1975 degrees celsius) at an ultra-low furnace temperature of <120 degrees celsius (or even at room temperature in a most recent work) to achieve ~97-98% of the theoretical density in 30 seconds; and (c) fabricating a new class of high-entropy, ultra-high-temperature ceramics, including (Hf0.2 Zr0.2 Ta0.2 Nb0.2 Ti0.2)B2 and other metal diborides with a unique quasi-2D high-entropy structure, as well as several other classes of high-entropy structural and functional ceramics.
Jian Luo graduated from Tsinghua University with dual Bachelor's degrees. After receiving his Ph.D. degree from M.I.T. in 2001, Luo worked in the industry for more than two years with Lucent Technologies Bell Laboratories and OFS/Fitel. In 2003, he joined the Clemson faculty, where he served as an Assistant/Associate/Full Professor of Materials Science and Engineering. In 2013, he moved to UCSD as a Professor of NanoEngineering and Professor of Materials Science and Engineering. He received a National Science Foundation CAREER award in 2005 (from the Ceramics program) and an Air Force Office of Scientific Research Young Investigator award in 2007 (from the Metallic Materials program). Luo was named as a Vannevar Bush Faculty Fellow (formerly National Security Science and Engineering Faculty Fellow) in 2014 and elected as a Fellow of the American Ceramic Society in 2016.