Mechanical-thermal coupling structural failure and in-situ deformation mechanism of cellular high entropy alloy lattice structures

To investigate the effect of temperature on the compressive strength of CoCrFeMnNi high entropy alloy with lattice structures prepared by powder bed fusion, the mechanical properties of the lattice structures at a temperature in a range from 20 degrees C to 900 degrees C were obtained through a self-developed in-situ mechanical-thermal coupling compressive system. The real-time deformation behaviors of the lattice structures were observed by an optical-infrared dual-spectrum imaging system. The experimental results indicated that the compressive strength, structural stiffness, and energy absorption of the specimens increased with the increasing temperature ranging from 20 degrees C to 600 degrees C during the load-bearing stage, accompanied by a fracture mode from cleavage step to dimple. At an elevated temperature of 900 degrees C, the specimens exhibited the worst compressive strength and structural stiffness but the highest densification strain. Significantly, the temperature-dependent deformation behaviors were revealed, as the gradually increased temperature promoted the deformation failure behavior transforming from "layer by layer" to "45 degrees shear band". The improved plasticity at elevated temperatures enhanced the deformation capacity of lattice structures, released the local concentrated load and effectively weakened the stress concentration.