Lee Hsun Lecture Series on Materials Science

Topic：Nucleation Studies in Titanium Alloys: The Role of Competing Phase Instabilities

Speaker: Professor Dr. Hamish L. Fraser

　　　　　Dept. of Materials Science & Engineering, The Ohio State University, USA

Time: 10:00am-11:30am, Wednesday, March 16, 2011

Venue: Room 403, R&D Center, IMR CAS

Welcome to attend!

Abstract:

During the recent past, the activities of CAMM have, in the main, been focused on the development of integrated computational materials science and engineering for application to titanium alloys. Specifically, the aim has been to develop new computationally-based research tools for the prediction of the interrelationship between microstructure and properties in these materials. This presentation will begin with a description of progress made in this endeavor. A major part of this research has involved the development of computational schemes, such as phase field modeling, to predict the evolution of microstructure as a function of thermo-mechanical processing. To make these modeling tools physically relevant, it is necessary that accurate mechanistic details be incorporated in the models. Regarding microstructural evolution, it is necessary that the mechanisms of nucleation of the α-phase from β-titanium be accurately modeled. These mechanisms are largely unknown, and consequently a major research thrust has been established to determine and characterize these nucleation mechanisms. The main part of this presentation will be focused on progress made in this latter research effort. The work has largely involved the application of aberration-corrected (scanning) transmission electron microscopy and atom probe tomography, to reveal structural and compositional details. It has been discovered that the nucleation process is markedly influenced by competing phase instabilities, specifically the phase separation of the β-phase, and the formation of the omega phase. The various results obtained and new insights developed will be presented. It will be shown that they can be used to understand the basis of the somewhat complicated heat-treatments used to develop microstructures that lead to optimum properties in new commercial alloys, such as Timetal 5553.