Prediction and observation of transformation induced plasticity behavior in CoCrNi multi-principal element alloys with in-situ synchrotron x-ray diffraction

Abstract

CoCrNi alloys are of interest as blast resistant materials, due to their high damage tolerance and toughness enhancing deformation mechanisms. As blast resistant materials need to exhibit toughness in dynamic conditions, studies of the effects of strain rate on the activation of transformation- and twinning-induced plasticity, or TRIP and TWIP, respectively, are required. This work examines a CALPHAD based approach to identifying TRIP capable alloys using the diffusionless transformation temperature, denoted as T0. The challenges associated with in-situ observation of phase transformations during dynamic deformation by state-of-the-art, synchrotron x-ray imaging and diffraction and strategies to minimize them are also explored. Using the CALPHAD based approach to predicting TRIP, five multi-principal element alloys (MPEAs) were selected as both likely and unlikely to experience TRIP, and then tested under dynamic conditions at the Advanced Photon Source at Argonne National Laboratory with simultaneous x-ray diffraction to monitor for potential phase transformation. TRIP behavior was observed in two alloys with the highest diffusionless transformation temperatures, while it was suppressed in alloys with lower diffusionless transformation temperatures. This is attributed to adiabatic heating effects during high rate deformation. TRIP behavior was also observed in a Co-rich MPEA by in-situ synchrotron x-ray diffraction at the Brazilian Synchrotron Light Laboratory during quasi-static straining at a range of temperatures, before TRIP behavior was suppressed at high temperatures.