Deformation behavior, microstructure evolution, phase transformation and plastic instability origin of powder metallurgy Al0.8Co0.5Cr1.5CuFeNi alloy during high temperature deformation

High temperature deformation behavior of powder metallurgy Al0.8Co0.5Cr1.5CuFeNi (containing BCC, FCC, sigma phase) at 1173-1323 K temperature range and 1-0.001 s(-1) strain rate range was investigated in detail. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) were used to analyze microstructure evolution and phase transformation. Transmission electron microscopy (TEM) was applied to examine tiny phase structure. The Arrhenius model and the artificial neural network (ANN) model for predicting flow stress were compared. The ANN model has significantly superior prediction performance. sigma phase was dissolved into BCC matrix as deformation temperature increased and strain rate decreased, and Al-Ni rich particles in BCC were greatly dissolved at higher temperature. After deformation, the average grain sizes of BCC and FCC were refined to 5.75-7.32 mu m, the orientation of FCC and BCC was quite random, and twins only appeared in FCC. The growth of dynamically recrystallized grains near phase boundary was mutually inhibited. High density dislocation accumulation at the BCC/sigma boundary under high strain rate induced the initiation of micro crack. Dislocation assisted grain boundary slip at low strain rate reduced the dislocation accumulation degree at BCC/sigma boundary to mitigate stress concentration. This mechanism suppressed the initiation of micro crack.