Atomistic Simulation of the Effect of H-Phase Precipitate on the Transformation Temperatures and Stress-Induced Phase Transformation in Ni-Rich NiTiHf

Abstract

AbstractPrecipitation hardening is considered the most feasible method for strengthening NiTiHf alloys. In order to design the optimum aging treatment to form precipitates, it is crucial to understand the effect of precipitates on the thermomechanical behavior of these alloys. In this research, the effect of H-phase precipitates was studied on the martensitic and superelastic behavior of Ni-rich NiTiHf. Using atomistic simulations, two scenarios for formation of precipitates, resembling the short and long aging time of the alloy, were considered. In the first case a single and large precipitate was embedded into the center of NiTiHf matrix, and in the second case eight fine precipitates were inserted into the model. Upon the calculation of the transformation temperatures, the models with precipitates showed higher austenite start and finish temperatures. Moreover, by simulating the stress-induced phase transformation, it was found that the presence of fine precipitates inhibits the formation of different martensite variants leading to smaller transformation strains.