Microstructure and mechanical properties of FeCoNiCrTi_x high entropy alloys by selective laser melting

The design idea of high entropy alloys (HEAs) has opened up a new era of alloy material science. Dense and crack-free FeCoNiCrTi_x HEAs (X = 0,0.4, referred to as Ti₀, Ti_0.4) were prepared by selective laser melting (SLM). By varying the laser power and scanning speed, the effects of laser process parameters on the mechanism of porosity formation, densification, organization, weaving evolution and mechanical properties of HEA specimens were systematically investigated. The results show that with increasing laser power or decreasing scanning speed, the tissues exhibit epitaxial growth across multiple melt pool boundaries, with a slight enhancement of crystal orientation in the <001>BD direction. The Ti_0.4 HEAs possess the best mechanical properties, with microhardness 426.61 HV_0.5, tensile strength 1355.49 MPa and elongation rate 7.54 %, respectively. The improved mechanical properties of Ti_0.4 HEA are mainly attributed to solid solution strengthening, fine grain strengthening (average grain size of about 4.2 μm) and discontinuous distribution of NiTi phase. The conclusions of the related studies provide an important theoretical basis for the selection of process parameters for the preparation of HEAs by SLM.