Formation Mechanism of Cellular Structure of NiCoCrFeAlEutectic High-Entropy Alloys by Selective Laser Melting

In this study, a NiCoCrFeAl eutectic high entropy alloy (EHEA) was prepared by selective laser melting (SLM). The sample was a cellular eutectic structure composed of BCC/B2 cells and FCC cell boundaries. The results show that under the extremely high-temperature gradient and cooling rate of selective laser melting, the microstructure characteristics of cellular eutectic produced by strong non-equilibrium solidification will be greatly affected by scanning speed and laser power. The reasons for the formation of the cellular structure are as follows: When the alloy composition slightly deviates from the eutectic point and becomes hypereutectic, it is beneficial to the formation of B2 cells/dendrites rather than eutectic under the condition of rapid growth caused by SLM rapid cooling. In addition, the size of the cellular structure decreases with the increase in scanning speed. However, at a lower scanning speed, the cyclic thermal loading time of the deposited materials is prolonged, which is beneficial to the diffusion and enrichment of elements and promotes the amplitude modulation decomposition process of the BCC phase in the cell. These results provide new insight into the formation and evolution behavior of the rapidly solidified structure of SLMed EHEAs.