Microstructures And Properties Of FeCoNiCr_0.5Al_x Single/Dual Phase High-Entropy Alloy Prepared Via L-PBF

High-entropy alloy has a multi-principal character.Its appearance breaks the traditional alloy design concept and is easy to form a simple solid solution,which makes it have excellent comprehensive properties.Generally,high-entropy alloys have high strength,high hardness,good plasticity,better wear resistance and corrosion resistance.High-entropy alloys can adapt to an application scenario with severe condition,so they have become a research hotspot in recent years.In this paper,FeCoNiCr_0.5Al_x（x=0,0.2,0.8）high-entropy alloys are prepared by laser powder bed fusion（L-PBF）.On the basis of determining the printing layer thickness（t）,by adjusting other printing process parameters,including laser power（P）,scanning speed（v）,hatching space（h）,to obtain alloys with good forming quality and dense structure.By adjusting the content of Al,the effects of Al addition and the characteristics of L-PBF technology on the solidification structure and mechanical properties of the alloy and the relationship between the deformation mechanism and the microstructure of the alloy were studied.For FeCoNiCr_0.5 high-entropy alloy,when h=70μm,t=30μm,the optimum printing process parameters are P=160W,v=1000mm/s.On the XOY plane,the grain size is between 40-60μm,with an equiaxed crystal morphology,and the yield strength,tensile strength and elongation are 492 MPa,546 MPa and 49%,respectively;on the XOZ plane,the formation of columnar grains with a length of 80-100μm were obtained,and the yield strength,tensile strength and elongation were 547 MPa,642 MPa and28%,respectively.The stable deformation behavior of the alloy is attributed to the formation of deformation twins in the<111>direction.For FeCoNiCr_0.5Al_0.2 high-entropy alloy,when h=70μm,t=30μm,the optimal printing process parameters are P=140W,v=830mm/s.The anisotropy of microstructure is similar to that of FeCoNiCr_0.5,on the XOZ plane,its yield strength,tensile strength and elongation are 510 MPa,590 MPa and 47%,respectively;on the XOY plane,its yield strength,tensile strength and elongation are 587 MPa,670 MPa and 27%,respectively.It has a similar deformation mechanism to FeCoNiCr_0.5,and the increase of strength and work hardening rate is due to the solid solution strengthening effect of Al.For FeCoNiCr_0.5Al_0.8 high-entropy alloy,when t=30μm,the optimal printing process parameters are P=200W,v=1250mm/s,h=110μm.It has excellent comprehensive mechanical properties.The compressive strength,compressive yield strength and fracture strain on the XOY plane are 2384 MPa,1458 MPa,and 23%,respectively;on the XOZ plane,they are 2031 MPa,1250 MPa,and 29%,respectively.The excellent comprehensive mechanical properties are attributed to the solidification structure of the alloy,where the matrix is BCC/B2 phase and FCC phase is distributed at the grain boundary.The B2 phase nanoparticles produced by spinodal decomposition are dispersed in the matrix,resulting in precipitation strengthening;the FCC phase distributed at the grain boundary ensures the plasticity of the alloy.