Role of titanium carbides on microstructural evolution of Ti-35V-15Cr-0.3Si-0.1C alloy during hot working

Abstract

The present study is to systematically investigate the role of titanium carbides on microstructural evolution of a burn resistant titanium alloy Ti-35V-15Cr-0.3Si-0.1C, especially on DRX and its kinetics under different deforming conditions during hot compression. First, a particle stimulated nucleation (PSN) phenomenon is found responsible for the pervasive dynamic recrystallization (DRX) in the material, in which DRX grains (or subgrains) prefer to form in the vicinity of titanium carbides (TiCx). And the morphology and distribution of TiCx can be altered by processing, which means the number of potential nuclei and the resultant recrystallization may be controlled by controlling the working process. Second, it is found that DRX fraction and DRX (sub) grain size are all deforming parameters (deformation temperature, strain and strain rate) dependent, and DRX kinetics is investigated by quantitative metallography analysis. The kinetics for DRX initiated by PSN in the present material follows the Avrami equation, which is consistent with the conventional DRX kinetics. The difference for this alloy is that only a small critical strain (<0.2) is needed for DRX initiation but a very large strain for fully recrystallization, which can be attributed to the special DRX initiation mechanism (PSN) and the sluggish DRX kinetics nature of beta-Ti matrix. Third, the relationship between DRX grain size (d) and the corresponding Zener-Hollomon parameter (Z) follows the equation: Zd2.95=e24.58. At last, by a billet cogging experiment, it is confirmed that multi-directional deformation can fully break down coarse TiCx and promote PSN, leading to a fine and homogeneous microstructure.