The Microstructure Evolution and Processing Map of Ni-18.3Cr-6.4Co-5.9W-4Mo Superalloy During Hot Deformation

Abstract

The processing map and microstructure evolution of Ni-18.3Cr-6.4Co-5.9W-4Mo superalloy were investigated in the temperature range of 1010-1160 °C and strain rate range of 0.001-1 s−1 by means of hot compression tests. According to the processing map, the optimum processing parameters were located in the temperature range of 1100-1160 °C and strain rate range of 0.01-0.3 s−1. The carbides in the alloy contributed to form a fine grain microstructure. In addition, four different instability criteria of Prasad, Gegel, Malas, and Murty were used to predict the unstable domains in the processing map. Meanwhile, the microstructure observations revealed that the unstable domain predicted by Murty’s instability criterion was very effective at high strain rate, which was the best choice for the studied alloy. Furthermore, the electron backscattered diffraction technique was used to detect the Σ3 boundaries and the adiabatic shear bands in the alloy. The results revealed that the fractions of Σ3 boundaries in the alloy deformed at 1100 °C/0.01 s−1 and 1160 °C/0.1 s−1 reached about 25 and 27%, respectively. Meanwhile, the fraction of low-angle grain boundaries and dislocation density were relatively high in the adiabatic shear band.