Deformation and fracture behavior of in-situ Ti composites reinforced with TiB/nano-sized particles

^a State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
^b Shanghai Key Laboratory of Advanced High Temperature Materials and Precision Forming, Shanghai 200240, China
^c Shanghai Spaceflight Precision Machinery Institute, China Aerospace Science and Technology Corporation, Shanghai 201600, China

^* Corresponding author. Email address: hyuf1@sjtu.edu.cn (Yuanfei Han), luweijie@sjtu.edu.cn (Weijie Lu).

Abstract

The hot deformation and fracture behavior of TiB/nano-sized particulate reinforced titanium matrix composites were investigated. The effect of reinforcement contents and initial structures on the isothermal deformation and fracture characteristic were investigated through microstructure analysis, tensile tests and crack propagation tests. It was found that the optimal working parameters for Ti composites is determined at 900-950°C/0.01-0.1 s-¹, which is associated with the continuous dynamic recrystallization of primary a grains and dynamic globularization of lamellar α. The necklace recrystallization was observed in β phase region, and the instability mechanisms include inhomogeneous deformation and breaking or debonding of TiB whiskers. Additionally, the addition of reinforcements refines α phases, decreasing the lamellar α width. The aspect ratio of TiB is much higher with the increase of reinforcement content. Higher content (2.5 vol. % and 5 vol. %) brings about more broken reinforcements and defects, which result in brittle fracture in Ti composite. Reinforcements and defects are believed to be the key factors to determine the crack propagation. Intergranular cracking is the main cracking way in the region where there are few reinforcements. Defects caused by fractured TiB play a dominant role in diverting intergranular cracking to transgranular cracking.

Key words: Hot deformation, dynamic globularization, dynamic recrystallization, Titanium matrix composites