Clarifying the Hot Shear-Compression Deformation Behavior of a Ni-Mo Superalloy: Flow Characteristic and Microstructure Evolution

Abstract

Hot shear-compression deformation (HSCD) is a burgeoning research method to reveal both the innate macro-mechanical response and the micro-crystallology transformation of metal materials. Based on the specific shear-compression sample (SCS), HSCD behavior of a Ni-Mo superalloy at 1000-1150 °C and 0.01-1 s-1 was investigated by both physical and numerical simulations. Results showed that experimental stress ranged from 85 MPa to 250 MPa under different HSCD conditions. SCS was divided into three typical regions with various distortion degree, and the largest true strain occurred in slots with a value of 1.2. Through the Electron Back-Scattered Diffraction (EBSD) and Transmission Electron Microscope (TEM) analysis, dynamic recrystallization (DRX) was observed to gradually weaken as the strain declined. The main and auxiliary DRX mechanisms were discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), respectively. Twinning dynamic recrystallization (TDRX) occurred in the annealing twins. Besides, the nano-scaled grains nucleated and further refined the microstructure under 1050 °C-0.1 s-1 and 1000 °C-1 s-1. Coincidence site lattice evolution (CSLE) was promoted by the nucleation of DRX grains. Moreover, the unique “rainbow grains” with large continuous orientation changes from <001> through <110> to <111> were found under 1100 °C.

Keywords: Ni-Mo superalloy, Hot shear-compression deformation, Coincidence site lattice evolution, Dynamic recrystallization, Nano-scaled grains, "Rainbow grains"