Microstructure and properties of FeCoCrNi high entropy alloy produced by laser melting deposition

Abstract

In this paper, the laser melting deposition (LMD) technology was applied to fabricate FeCoCrNi high entropy alloy (HEA), and the microstructure of the deposited HEA (FeCoCrNi-LMD) was systematically studied. The width of the columnar grains was found to increase gradually from the bottom to the top of the material. The top layer consisted of equiaxed grains. Tensile stress and compressive stress were applied to the material along and perpendicular to the direction of columnar grain growth, respectively. Electron Backscatter Diffraction (EBSD) and transmission electron microscopy (TEM) were used to observe the changes in the microstructure and properties of the material under the applied stresses. It was found that the phase structure of the material did not change when the stress was applied, but the maximum polar density increased. After stretching, the Schmid factor decreased, resulting in strain hardening. Dislocations moved during the plastic deformation and their number increased, resulting in many small angle grain boundaries and subgrain boundaries. The dislocations concentrated at the grain boundaries, leading stress concentration at the grain boundaries. In addition, due to the differences in the distribution of elements between the grains and the grain boundaries, the properties of grain boundaries changed. Cracks were produced easily along the grain boundaries during the tensile test. Under the compressive stress (rolling), for the same amount of rolling deformation, as the width of the columnar grains increased from the bottom to the top of the FeCoCrNi-LMD, the size of the columnar grains increased. As a result, the columnar grains were inclined at an angle to the rolling direction, and the rolled specimen was bent.