Effects Of Al And Ti On Microstructures And Mechanical Properties Of CoCrNi Multi-principal-element Alloy

In recent years,multi-principal-element alloys are the new class of materials defined as alloys consisting of 3 or more principal elements with equimolar or nearly equimolar fractions.Compared with the traditional alloys,the multi-principal-element alloys exhibit many excellent properties,such as,high hardness,high strength,corrosion resistance and good high-temperature oxidation.In the present study,Al_xCoCrNi(x=0,0.1,0.2,0.3,0.4,0.5,0.6,0.8,1,1.2,denoted as Al-x afterwards)and Ti_xCoCrNi(x=0,0.1,0.2,0.3,0.4,denoted as Ti-x afterwards)were prepared by arc-melting and drop casting.The microstructure of the samples were investigated using X-Ray diffraction(XRD)and scanning electron microscopy(SEM).The mechanical properties material properties were tested by a material performance rig and Vickers hardness tester at room temperature.SEM results showed that the crystalline structure of the as-cast Al_xCoCrNi alloys changes from the initial face-centered cubic(FCC)structure to a duplex FCC plus body-centered cubic(BCC)structure and then a single BCC structure as the Al concentration is increased.In the range of 0?x?0.6,with the increasing Al,the tensile strength of the alloy is improved but accompanied with reduced ductility.For example,the tensile yield strength,ultimate strength and tensile elongation of Al-0.6 are 544 MPa,1109 MPa and14%respectively.Specifically,the Al-0.8,Al-1 and Al-1.2 alloys are brittle material.The hardness increase with the increase of Al contents,and the Al-1.2 alloy exhibits the hightest hardness wih a value of 659 HV.The microstructures of the as-cast Ti_xCoCrNi alloys change from the initial single FCC structure to a duplex FCC plus(Ti+Ni)-rich phase structure and then FCC+(Ti+Ni)-rich phase+Cr-rich phase structure as the Ti concentration was increased.With the increase of Ti concentration,the compressive yield strength increases at first and then decreases,the Ti-0.3 alloy exhibits the hightest yield strength wih a value of1712.6 MPa.In the terms of plasticity,the Ti-0,Ti-0.1 and Ti-0.2 alloys are plastic materials.The compressive ratios of Ti-0.3 and Ti-0.4 alloys are 13.6%and 27.9%,respectively.The hardness also increase with the increase of the Ti contents,and the Ti-0.4 alloy exhibits the hightest hardness wih a value of 608 HV.