Microstructure refinement of a cast high entropy alloy by thermomechanical treatments

Abstract

This work investigates the hot compressive behaviour of a cast high entropy alloy. The alloy is subjected to four different thermomechanical treatments to refine the as-cast microstructure: hot compression tests at constant strain rates (0.001s−1 and 1s−1), hot compression tests with strain rate jumps (between 0.001s−1 and 1s−1), multi-stage hot deformation with holding intervals of 1 and 5 min, and hot compression at 0.1s−1 followed by annealing. The three first tests were carried out at 1100 °C and the deformation step of the last type was carried out at 1050 °C followed by annealing at 1150 °C. The deformation at 0.001s−1 promotes dynamic recrystallisation. Dynamic recrystallisation occurs when jumping from 1s−1 to 0.001s−1 and does not occur if the jump is from 0.001s−1 to 1s−1. Multi-stage interrupted tests show that 1 min holding between the stages promote dynamic recrystallisation, while static recrystallisation occurs more pronouncedly for 5 min inter-stage holding. Due to the large initial grain size, deformation does not occur homogeneously within the grains, and heterogeneous static recrystallisation occurs within the deformed specimen. Whether the alloy is solution heat treated or deformed in the as-cast condition does not affect the recrystallisation behaviour. Overall, refining the coarse cast microstructure of the investigated alloy is possible, although more deformation steps are needed to produce a homogeneous microstructure.