Role of deformation temperature and strain rate on microstructural evolution of hot compressed Nb–Si based ultrahigh temperature alloy

Microstructural evolution of a Nb–Si based ultrahigh temperature alloy during hot compression at different temperatures and strain rates has been investigated. The results show that the fraction of Nbss recrystallized grains is larger at higher temperatures or lower strain rates. The variation of Nbss grain size (d) with deformation temperatures (T) and strain rates (ε˙) in steady-state flow conforms to a relation: [Formula presented]. Cracking has been significantly exacerbated and continuous dynamic recrystallization (CDRX) has been substantially restrained in Nb₅Si₃ when deformation temperature decreases from 1350 to 1250 °C or strain rate increases from 0.001 to 0.1 s⁻¹. Nb₅Si₃ flakes have broken up into smaller particles via boundary splitting during hot deformation. Both the fragmentation of Nb₅Si₃ flakes and the composition homogenization in Nbss/Nb₅Si₃ eutectics have been accelerated with increase in deformation temperature from 1250 to 1350–1410 °C at 0.001 s⁻¹, but slowed down at a higher temperature of 1500 °C and restrained at higher strain rates of 0.01–0.1 s⁻¹. The correlation between microstructural evolution and the strain rate sensitivity has been discussed.