题目：The Role of Structural Instabilities on Microstructural Evolution in Titanium Alloys

报告人：Prof. Hamish L Fraser

时间：10月24日（周二）10:00-12:00

地点：师昌绪楼403会议室

The Role of Structural Instabilities on Microstructural Evolution in Titanium Alloys

Hamish L Fraser

Center for the Accelerated Maturation of Materials, The Ohio State University,
1305 Kinnear Road, Columbus, OH 43221, USA

Abstract

The subject of microstructural evolution in metastable beta titanium alloys has attracted much attention recently. Thus, compared with conventional microstructures in alpha/beta Ti alloys, typically involving fairly coarse lamellae of the alpha phase in either the colony or basketweave arrangement depending on heat treatment conditions, various size scales of refined intragranular alpha microstructures can be produced in metastable beta Ti alloys. In this current research, three different size scales of alpha microstructure, termed refined alpha, more-refined alpha and super-refined alpha microstructures, have been characterized in the same metastable beta Ti alloy, Ti-5553. These various distributions have been produced by exploiting the influences of compositional and/or structural instabilities on the   transformation, using various non-conventional transformation pathways. The refined alpha microstructure is formed by the mechanism of pseudo-spinodal decomposition, involving thermally-activated compositional fluctuations about the appropriate Co(T) composition within the beta matrix. Metastable phases, such as the omega phase and bcc structure beta-prime phase, can also alter the local concentration and/or structure and therefore potentially affect subsequent alpha precipitation. The more-refined and super-refined alpha microstructures are formed by exploiting this metastability, specifically the indirect and direct influences of the pre-formed, uniformly distributed metastable omega phase in a beta phase matrix. The formation mechanisms of these various forms of ultra fine alpha microstructures will be compared and contrasted in terms of these nano-scale compositional and/or structural instabilities in the beta phase matrix in metastable beta titanium alloys. The support of the US NSF under grant DMR-1309270 and DMREF grant DMR-1435483 is gratefully acknowledged.

Hamish L. Fraser 教授简介：

　　Hamish L. Fraser教授1972年毕业于英国伯明翰大学，获得物理冶金学博士学位。1973 年加入美国伊利诺伊大学，至1989年间在伊利诺伊大学分别担任助理教授，副教授及教授。1989年至今任美国俄亥俄州“摄政王杰出学者” 和俄亥俄州立大学材料科学与工程系教授，俄亥俄州立大学材料加速熟化中心主任。Hamish L. Fraser 教授曾担任美国联合技术研究中心高级研究员，德国哥廷根大学高级洪堡访问学者，英国剑桥大学及利物浦大学客座教授。1988年起任英国伯明翰大学材料科学与工程系荣誉教授，2014年起任南非尼尔逊曼德拉大学荣誉教授，并担任澳大利亚莫纳什大学以及美国北德州大学兼职教授。

　　Hamish L. Fraser教授是物理冶金学领域及电子显微学领域国际著名专家，在先进电子显微技术及其应用，先进金属材料加工工艺，以及集成计算材料科学与工程等方面开展了长期系统的研究工作。Hamish L. Fraser教授是美国金属协会（ASM），美国矿物、金属和材料协会（TMS），英国材料学会、矿物和冶金协会（IOM3）及美国显微学协会会士，也是美国航空发动机材料ICME(集成计算材料工程)的创建者之一。Hamish L. Fraser教授曾任美国国防部研究与工程咨询委员、美国科学院全国材料咨询委员会委员、北约航空航天研究理事会顾问委员、英国科学与工程研究理事会材料战略工作组成员、美国Los Alamos国家实验室材料研究部评估委员会成员和剑桥大学材料系校外咨询委员会成员，并三度担任美国空军实验室科学顾问委员会成员。

　　Hamish L. Fraser教授在国际著名期刊发表学术论文400余篇，在国际会议及访问中受邀报告300余次，培养了超过50名博士生及30余名硕士研究生。