MSE Seminar: Yufeng Zheng, Nucleation Mechanisms of Refined Alpha Microstructure in Beta Titanium Alloys

PhD Candidate advised by Dr. Hamish Fraser, Department of Materials Science and Engineering, The Ohio State University

Abstract

Due to the combination of high strength, great deep-hardenability and excellent corrosion resistance, Ti-5Al-5Mo-5V-3Cr (Ti-5553) has become a promising beta titanium alloy for application in aerospace components. Understanding phase transformations in Ti-5553 is integral to manipulating its structural/property interrelationships. A detailed study of the structure and compositional change at the initial stage of α precipitation in β matrix is beneficial to the understanding of BCC structure to HCP structure transformation mechanism. For the work to be presented, the characteristics and transformation mechanisms of refined and super-refined intragranular alpha phase in beta titanium alloys were studied using advanced electron microscopy characterization techniques. Additionally, the microstructural evolution in Ti-5553 during two categories of heat treatments was characterized using scanning electron microscopy, transmission electron microscopy and 3D atom probe. Upon step quenching from above the beta transus temperature and isothermally holding in the intermediate temperature range, refined alpha precipitates were homogeneously observed in β matrix. Upon continuous heating up from the as-quenched state, super-refined alpha precipitates were observed in Ti-5553. The structural, morphological, crystallographic and compositional characteristics of the refined and super-refined alpha precipitates during the initial stages of precipitation will be discussed in detail. Non-classical nucleation mechanisms are proposed to fully explain the features of the two types of refined alpha microstructure. The proposed transformation mechanisms were in agreement with phase field modeling simulation and thermodynamic calculations. Therefore, a thorough understanding of phase transformation mechanisms controlling refined and super-refined alpha microstructure and the critical thermal treatment conditions to obtain these two types microstructure will be introduced.

 

Bio

Yufeng comes from China and receives his B.S. in Applied Physics from University of Science and Technology of China (USTC). In September 2007, Yufeng joined Dr. Hamish L. Fraser’s group as a Ph.D. student in the Department of Materials Science and Engineering of The Ohio State University and received his master degree in the year of 2010. Yufeng’s research interest mainly consists of physical metallurgy of titanium alloys and advanced electron microscopy characterization techniques. His research focuses on using electron microscopy and other modern characterization techniques to study transformation mechanisms of various phase transformations in titanium alloys.

In the spare time, Yufeng is a soccer fan and amateur soccer player. He was the co-captain of Chinese soccer team at The Ohio State University and the vice president of Benchball club for two years, which is an official OSU sports club. He plays soccer in the intramural soccer game almost every quarter and sometimes in city league. Yufeng and his team have visited many nearby cities, such as Cincinnati, Cleveland and Pittsburgh to play friendly soccer games and tournaments. With his team, Yufeng has played in the semi-final of world cup soccer tournament at The Ohio State University and won the champion of Mid-west Chinese soccer tournament in the year of 2011. In March 2013, Yufeng just won the champion of Chinese indoor soccer tournament.