Research On Microstructure And Properties Of Al_0.3CrFe_1.5MnNi_x High Entropy Alloy

High entropy alloys are composed of 5 or more than 5 main elements.Each element has equal(near)atomic ratio.Because of the high mixing entropy,the alloy is generally formed with a simple solid solution structure and has excellent performance.In this paper,A10.3CrFei.sMnNix(x=0.25,0.5,0.75,1.0)series of high entropy alloys were prepared.The phase structure,microstructure and properties of as-cast and heat-treated alloys were studied by XRD,OM,SEM,compression tests and so on.The results of the research indicate that:(1)In the as-cast condition,with the increasing of the content of Ni,the crystal structures of Alo.3CrFe1.5MnNi0.25 and Al0.3CrFe1.5MnNi0.5 alloys are of BCC,while the Alo.3CrFe1.5MnNi0.75 and Al0.3CrFe1.5MnNi1.0 alloys are of BCC+FCC structure,and their microstructures are dendritic structure.For Alo.3CrFe1.5MnNi0.25 and Al0.3CrFe1.5MnNi0.5 single-phase alloys,Cr elements are enriched in dendritic and Ni elements are enriched in interdendritic;for Alo.3CrFe1.5MnNi0.75 and Al0.3CrFe1.5MnNii.o dual-phase alloys,the crystal structure of dendrite with enrichment of Fe,Cr elements is BCC,FCC structure for interdendritic with enrichment of Ni.The analysis shows that the phase formation law of this system is inconsistent with the laws summarized in the literature.In this paper,the alloys crystal structure is not entirely determined by the VEC,but also affected by many factors such as atomic size difference,mixing entropy,solidification process and so on.In the as-cast condition,the hardness and yield strength of Al0.3CrFe1.5MnNi0.5 alloy are the largest,which are 389.7HV and 1361 MPa respectively.The plasticity of Al0.3CrFe,.sMnNi1.o alloy is the best and the compressive strain ups to 65%.(2)After aging treatment,the CrsFe6Mn8 precipitates exist in Al0.3CrFe1.5MnNix(x=0.25,0.5,0.75,1.0)high entropy alloys at and below 800℃.With the increasing of temperature,the segregation degree of dendrite structure decreases,and the composition of alloys are gradually homogeneous.The composition of Alo.3CrFe1.5MnNi0.25 alloys has been mostly homogeneous at 900℃ and CrsFe6Mn8 dissolved into the matrix,precipitated Al0.96Ni1.04 while the remaining three alloys which retained the dendritic structure after aging treatment at 900℃ are not completely homogenized,CrsFe6Mn8 phase was still found and no Al0.96Ni1.04 was formed.With the increasing of temperature,the size of precipitated phase of CrsFe6Mn8 in Al0.3CrFei.sMnNi1.0 alloys gradually increases.(3)Al0.3CrFe1.5MnNix(x=0.25,0.5,0.75,1.0)high entropy alloy has obvious aging hardening phenomenon after heat treatment.The hardness of Al0.3CrFe1.5MnNi0.5 alloy after being kept at 600℃ for 5h is 930.OHV,which is 112%higher than that of as-cast.The fracture strength of Alo.3CrFe1.5MnNio.25 and Al0.3CrFei.5MnNi1.0 alloys reached the maximum at 2070MPa and 2061MPa respectively.And Al0.3CrFe1.5MnNi1.0 still has higher strength after 900 ℃ for 5h.(4)It was found that Alo.3CrFe1.5MnNio.25 and Al0.3CrFei.5MnNii.0 alloys have better comprehensive performance after being kept at 700℃ for different hours.The hardness of Alo.3CrFe1.5MnNio.25 alloys reached 881.6HV after being kept at 700 ℃ for 24 hours.The hardness of Al0.3CrFe1.5MnNi1.0 alloys at 700℃ for 10h reached a peak of 630.5HV.The maximum compressive strength of the two kinds of alloys is 2275MPa and 2180MPa at 700℃ for 10h.