Topic: Enhancing stability of nanocrystalline alloys via the thermodynamic approach

Speaker: Dr. Tongjai Chookajorn (Researcher)

　　　　　　National Metal and Materials Technology Center (MTEC),
　　　　　　National Science and Technology Development Agency (NSTDA), Thailand

Time: 10:00-11:00, Tuesday, June 23^th, 2015

Venue: Room 468, Lee Hsun Building, IMR CAS

Welcome to attend!

Abstract：

Improvement in material properties as a result of grain size refinement to the nanoscale is often limited by an inherent tendency of these nanostructured materials to coarsen, especially at the high temperatures required for processing. The instability stems from a large volume fraction of grain boundaries that carry an intrinsic energy penalty but can be overcome by a consideration of the thermodynamics-based mechanism of interface energy relief via alloying. A Monte Carlo method that captures the physics of regular solution and grain boundary segregation in nanostructured alloys is developed, and in the proper limits, reproduces regular solution mixing and McLean-type grain boundary segregation. Depending on the mixing and grain boundary segregation tendencies, the model predicts several alloy configurations, including stable nanocrystalline structures, in which grain boundary segregation of solute reduces the system energy below that of any bulk states, and duplex nanocrystalline structures, in which phase separation is most preferred, followed closely by grain boundary segregation. Requirements for stability are identified and the framework for alloy design will be presented.