Cryogenic Dynamic-Mechanical Property and Microstructure of a Selective Laser Melting FeCoNiCrMo0.2 High-Entropy Alloy

Cryogenic dynamic mechanical properties are the key indicators for the application of a selective laser melting FeCoNiCrMo 0.2 high-entropy alloy (SLM-FeCoNiCrMo 0 . 2 HEA) in the impact-related fields under the cryogenic temperature. When the SLM-FeCoNiCrMo 0 . 2 HEA specimens are impacted at 77 K with a strain rate of 1300 s -1 , the specimens exhibit excellent impact energy and ultimate compressive strength, which are 1756 MPa and 210 MJ/m 3 , respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the microstructure before and after the cryogenic impact deformation. When the volumetric energy density is 62.5 J/mm 3 , molten pool overlap rate, columnar grain size and grain size of cellular structure are 15.3 %, 21.7 mu m and 476 nm. Columnar grain is composed of cellular structure with different orientations. There are numerous dislocation tangles and segregation of the Mo element at the cellular structure boundaries. After multiple impacts at 77 K, microcracks appear on the columnar grain boundary. Cellular structure has the function of the coordinated deformation at cryogenic temperature. And the columnar grain boundaries are prone to microvoids and microcracks due to the inconsistent coordination of different cellular structures. Cellular structure plays an important role in improving the cryogenic dynamic mechanical properties of the SLM-FeCoNiCrMo 0.2 HEA. This work provides theoretical guidance for the strengthening of the cryogenic dynamic mechanical properties of the SLM-FeCoNiCrMo 0 . 2 HEA.