Superposition of large plastic shear on high pressure in rotational diamond anvil cell (RDAC) leads to numerous new phenomena, including drastic reduction in phase transformation (PT) and chemical reaction pressure and appearance of new phases that were not obtained without shear [1-3]. Here, four-scale theory was developed for high-pressure mechanochemistry and corresponding simulations were performed. Molecular dynamic simulations were used to determine crystal lattice instability conditions under action of all six components of the stress tensor, which demonstrate strong reduction of PT pressure under nonhydrostatic loading . At the nanoscale, nucleation at various evolving dislocation configurations is studied [5-6] utilizing developed phase field approach [7,8]. Possibility of reduction of PT pressure by an order of magnitude due to stress concentration at the shear-generated dislocation pile up is proven. At the microscale, strain-induced and pressure-controlled kinetic equation is derived. This equation is utilized in the large-strain macroscopic theory for coupled PTs and plasticity. At the macroscale, the behavior of the sample in RDAC is studied using finite element approach [9-11]. Various experimental effects are reproduced. The obtained results offer new fundamental understanding of strain-induced PTs under pressure in RDAC and methods of controlling PTs and searching for new high-pressure phases. They also propose new characterization of high pressure PTs in RDAC. Similar approach is applied for traditional high-pressure torsion. Obtained results are applicable for various mechanochemical technologies (like ball milling) and for interpretation of geophysical data.
About the Speaker
Professor Valery Levitas is currently Vance Coffman Faculty Chair Professor at Departments of Aerospace Engineering, Mechanical Engineering, and Material Science and Engineering of ISU and Faculty Scientist at Ames Laboratory. He works for more than 30 years on different aspects of phase transformations, plastic deformations, and their interactions in various materials. He published 375 scientific papers, including 3 books, 10 book chapters, and 238 refereed journal papers, as well as 11 patents. He brought to the USA a unique device, rotational diamond anvil cells, and initiated experimental and theoretical research on interaction between phase transformations and plasticity under high pressure. Among recent awards, Valery received Khan International Medal Award for outstanding contributions to the field of plasticity (2017), ISU Award for Outstanding Achievement in Research (2016), Alexander von Humboldt Foundation Award for alumni (2012), and Honorable Doctor in Materials of the Institute for Superhard Materials, Kiev, Ukraine (2011).
Host: Professor Mariana Kersh