A study on the microstructure and mechanical behavior of CoCrFeNi high entropy alloy fabricated via laser powder bed fusion : experiment and crystal plasticity finite element modelling

Abstract

Additive manufacturing facilitates the design of high entropy alloys (HEAs) with well-performing properties compared to conventional manufacturing methods. However, a significant obstacle to the industrial application of the equimolar CoCrFeNi HEA fabricated through additive manufacturing is the detrimental impact of thermal cracks on its performance. Here, thermal crack-free CoCrFeNi HEAs with enhanced mechanical properties were obtained by optimizing the energy input in laser powder bed fusion (LPBF). The lower energy input resulted in finer grains, leading to simultaneously improved strength and ductility compared to the one fabricated via higher energy input. To understand the relationship between the microstructure and mechanical properties, crystal plasticity element modelling (CPFEM) was employed to accurately model the experimental results. Using the collected constitutive parameters for CoCrFeNi HEA after CPFEM, in-situ tensile modelling was implemented on a converted orientation map of an as-LPBF CoCrFeNi sample. The CPFEM results reveal that the appearance of deformed twins during the initial plastic deformation stage is attributed to a complex distribution of shear strain on the grain boundaries. The interaction between the deformed twins and dislocation motion emerged as the primary deformation mechanisms in the as-LPBF CoCrFeNi HEA, resulting in complex stress and strain distributions. By combining experimental data with modelling techniques, a viable approach to comprehending the detailed deformation mechanism of deformed twins was established.