Understanding the Role of Multi-scale Reinforcements on Severe Plastic Deformation of Titanium Matrix Composites

Abstract

Titanium matrix composites (TMCs) reinforced with different TiBw and La2O3p content were successfully processed by equal channel angular pressing (ECAP), and the role of reinforcements on the microstructure and mechanical properties were investigated. The results show that the addition of reinforcements accelerates continuous dynamic recrystallization (CDRX) and promotes the formation of new ultrafine grains (200 to 500 nm) in ECAPed TMCs. Micron-scale TiBw accelerates recrystallization by particle-stimulated nucleation and the increasing effective strain. CDRX occurs more easily near TiBw tips due to the load-bearing effect. By contrast, nano-scaled La2O3p retards the migration of grain boundaries through Zener drag effect and promotes the evolution of CDRX. The strength of ECAPed TMCs is improved significantly and reinforcements enhance the contribution of grain-refinement strengthening. The TMCs with 1.2 vol pct reinforcements exhibited the largest improvement in total strength, which is 5 times and 3 times of those with 0 vol pct and 2.4 vol pct, respectively. The elongations of both forged and ECAPed TMCs decrease with increasing reinforcement content owing to TiB whisker fracture and interface debonding and the diminishing strain hardening capacity.