Hot deformation behavior and processing map of a powder metallurgy Ti–22Al–25Nb alloy

Abstract

Powder metallurgy (P/M) Ti–22Al–25Nb alloy billets were fabricated by hot pressing (HP) from argon atomized pre-alloyed powders at a temperature of 1050°C under a pressure of 35MPa, sintering for 1h. Cylindrical specimens from HP’ed billets were compressed within the deformation temperature range of 950–1070°C using strain rates from 0.001 to 1s−1 to a height reduction of 50%. Processing maps at strains of 0.4 and 0.6 were constructed on the basis of dynamic material model (DMM) theory by using the flow stress data obtained from hot compression tests. The processing map at a strain of 0.6 reveals a single dynamic recrystallization (DRX) domain and three lamellar globularization domains. Furthermore, an instability region is exhibited at temperatures lower than 980°C and strain rates higher than 0.1s−1. The hot deformation behavior regimes represented by DRX, lamellar globularization and the instability flow have been discussed in reference to microstructural evolution during hot compression. Kinetic analysis of the flow stress data at a strain of 0.6 was investigated. The results indicate that dislocation slip and climb (DSC) are likely to be the deformation mechanism responsible for the stability domains.