University of Wisconsin-Madison

报告摘要：

As one of the main reactions that develop during heating of metallic glasses primary crystallization has received a continued attention to determine the phase selection and some kinetic behavior. The interest on primary crystallization is related to the enhanced strength and superior magnetic properties associated with the nanocrystal dispersion that forms during reaction. To provide for a directed control of the nanocrystallization a more complete understanding of the reaction kinetics is essential, especially for the nucleation stage. Conventional thermal analysis and TEM determination of nanocrystal populations are useful but can only cover a limited range of kinetic behavior. The recent advent of nanocalorimetry (Flash DSC) offers a significant extension of the kinetic range for study. The application of Flash DSC to the primary crystallization of amorphous Al1 and Zn2 alloys highlights the capability to measure the nucleation delay time that provides critical data for a quantitative nucleation kinetics model and for the elaboration of a complete TTT diagram3. For amorphous Fe base metallic glasses, the Fe nanocrystals formed during primary crystallization are known to be responsible for the enhanced soft magnetic behavior. In this case the size refinement of the Fe nanocrystals is the key objective to maximize the magnetic performance, but despite repeated attempts a size refinement below 10-15 nm has not been possible. The application of Flash DSC over an extended kinetic range has identified the influence of diffusion field impingement which inhibits further nucleation as the likely cause of the size refinement limitation4. As another use of Flash DSC, the transition has been elucidated between two amorphous phases in D-Mannitol5. The transition is related to a change in hydrogen bonding and involves an enthalpy change equivalent to about two-thirds of the crystallization enthalpy. The kinetics of the reaction between the two amorphous phases covers a range from conventional nucleation to a transition to a continuous or spinodal reaction. These examples document the enhanced capability of Flash DSC to examine new domains of kinetic behavior.

References

1. Y. Shen, J.H. Perepezko, Jnl. Non-Cryst. Solids, 502 (2018) 9-14.

2.T. Duan, W. Kim, M. Gao, J.H. Perepezko,  Jnl. Non-Crystalline Solids,  627 (2024) 122823.

3. W. Kim, T. Duan, E.S. Park, J.H. Perepezko, Acta Mater. 286 (2025) 120754.

4. W. Kim, T. Duan, J. H. Perepezko,  Scripta Mater. 225 (2023) 115155.

5. C. Cao, W. Tang, J. H. Perepezko, J. Chem. Phys. 157 (2022) 071101.

报告人简介：

Professor John H. Perepezko is the IBM-Bascom Professor in the Department of Materials Science and Engineering at University of Wisconsin-Madison. He earned his B.Sc. degree and M.Sc. degree from Polytechnic Institute of New York, and the Ph.D. degree from Carnegie-Mellon University. He specializes in the mechanism, kinetics and thermodynamics of phase transformations, nucleation during solidification, amorphous metals, properties of metal powders, rapid solidification processing, metastable phases, intermetallic alloys, oxidation, composite materials, coatings, phase stability, modeling, materials design  and the structure and characteristics of interfaces in metals. He has published nearly 500 research papers, is a Fellow of TMS, ASM International, JSPS, MRS and AAAS and was elected to the National Academy of Engineering in 2004 for his innovations in solidification processing to obtain useful microstructured, nanostructured, and amorphous materials. His honors and awards include the ASM Bradley Stoughton Award, the Alexander von Humboldt Stiftung Forschungspreise, the TMS Bruce Chalmers Award, TMS W. Hume-Rothery Award, ASM International Gold Medal, ASM International Albert Easton White Distinguished Teacher Award, Adjunct Professor-Tohoku University and the Tokyo Institute of Technology and the Helmholtz Gemeinschaft International Fellow Award.  He has served on the board of directors for the ASM-Milwaukee Chapter for more than twenty years. He has served on the editorial board for several journals including the International Journal of Powder Metallurgy, Intermetallics, Materials Science Foundations, Acta Materialia and Scripta Materialia. Since taking the faculty position at the University of Wisconsin in Madison from 1975, he has mentored more than 60 masters and doctoral students, six of whom have become professors at universities.

邀请人：汪卫华

联系人：罗鹏

联系电话：82649267