Microstructural evolution and high-temperature deformation mechanisms in TiB whisker-reinforced near-α titanium matrix composites after superplastic tensile deformation

Abstract

TiB whisker-reinforced Ti65 (TiBw/Ti65) composites exhibit significant potential for aerospace hot-section components owing to their excellent high-temperature stability below 750 °C. However, their engineering application is limited by the degradation in room-temperature plasticity caused by the reinforcement phase. This study systematically investigated the superplastic deformation behavior and flow stress evolution of a TiBw/Ti65 composite via high-temperature tensile tests conducted at temperatures ranging from 900 °C to 975 °C and strain rates from 0.00037 s^-1 to 0.01 s^-1. A maximum elongation of approximately 105% was observed at 950 °C and 0.001 s^-1. The results demonstrated that temperature and strain rate profoundly influence the true stress-strain response, which was categorized three characteristic types: flow softening (Type I), dynamic balance (Type II), and strain hardening (Type III). Microstructural analysis confirmed that dynamic recrystallization (DRX) is the dominant softening mechanism. Silicides and TiBw promote both continuous and discontinuous DRX via particle-stimulated nucleation (PSN), while simultaneously inhibiting grain coarsening through the Zener pinning effect. Furthermore, a highly accurate phenomenological strain-compensated Arrhenius model was established (R > 0.99, AARE = 4.43%) to predict the flow stress. The superplastic deformation is dominated by grain boundary sliding (GBS), which is synergistically coordinated by dislocation slip/climb, diffusion creep, and DRX. This research provides a theoretical foundation for optimizing the superplastic forming processes of complex components.