EFFECT OF PRIOR PARTICLE BOUNDARY ON DEFORMABILITY OF POWDER PROCESSED TURBINE DISK ALLOY

摘要

Powder metallurgy (P/M) process has been applied to high strength turbine disk alloy. It is known that P/M alloy shows characteristic microstructure such as prior powder boundaries (PPB) compared to conventional cast and wrought (CW) alloy. High temperature tensile test has conducted on CW and P/M processed alloy720Li in order to reveal the effect of temperature and strain rate on deformation behavior to discuss the effect of microstructure derived from P/M process on deformability. Fracture mode of the P/M material changed from grain interior fracture to fracture around large PPB with increment of strain rate. In addition, samples ruptured at higher temperature showed grain boundary fracture regardless of strain rate. On the other hand, CW material showed good deformability with chisel point fracture in whole temperature and strain rate condition range. In the P/M material, melting of grain boundary occur at super solvus temperature condition. Large PPB acts nucleation site of voids at higher strain rate condition. Precipitation strengthening by γ' phase degrade deformability at sub solvus temperature condition. However, deformability near solvus temperature and low strain rate condition in as HIPed P/M material increased with fine grain size distribution in spite of presence of large grain resulting from PPB.