Microstructure,Mechanical And Tribological Properties Of Al_0.2Co_1.5CrFe_xNi_1.5TiC_y High Entropy Alloy System

Being different from the conventional alloy,high entropy alloys?HEAs?is a new type of alloy material which contain multiple elements.This alloy has simple microstructure and outstanding thermal stability and maybe become the next-generationhightemperatureresistancem aterials.Inthispaper,by spark plasma sintering?SPS?technique.Commercially available aluminum,cobalt,chromium,iron,nickel,titanium,and graphite powders are used as the starting materials.Their microstructure,mechanical properties and tribological properties are studied in detail.The main results are listed as follows:?1?Al_0.2Co_1.5Cr Fe Ni_1.5Ti HEA contains two phases,a high entropy solid solution phase with FCC crystal structure and?Co Ni?₃Ti intermetallic phases,some needle-like?Co Ni?₃Ti phases form a typical Widmanstatten structure.The addition of carbon effectively surpressed the formation of?Co Ni?₃Ti phases and the microstructure of Al_0.2Co_1.5Cr Fe Ni_1.5Ti C_y HEAs transforms into FCC high entropy solid solution phase and Ti C ceramic phases.The lattice parameter of FCC high entropy solid solution phase decreases with increasing of carbon content.It is the main reason of forming Ti C ceramic phases that the mixture of negative enthalpy between titanium and carbon.Increasing the iron molar ratio of Al_0.2Co_1.5Cr Fe Ni_1.5Ti C_0.4 from 1.0 to 1.2 also decreases the lattice parameter of FCC high entropy solid solution phase of Al_0.2Co_1.5Cr Fe_1.2Ni_1.5Ti C_0.4 HEA,meanwhile improved effect of dispersion distribution of Ti C ceramic phase.?2?With carbon content increasing,Vickers hardness and compressive yield strength of Al_0.2Co_1.5Cr Fe Ni_1.5Ti C_y gradually decreases and compressive strength and fracture toughness show atendence of increase first and then decrease which reaches a maximum at y=0.4 and y=0.6,respectively.Bending fracture morpphology gradually transforms from intergranular fractures and transgranular cleavage fractures into dimple fracture with carbon content increasing.The dimple generated by ductile fracture is the major characteristic of the bending fracture morphology of Al_0.2Co_1.5Cr Fe_1.2Ni_1.5Ti C_0.4 HEA.?3?At room temperature,the wear mechanism of Al_0.2Co_1.5CrFe_xNi_1.5TiC_y?x=1.0,1.2;y=0,0.2,0.4,0.6,0.8,1.0?HEAs is surface fatigue wear.And the wear mechanism gradually transforms mild oxidational wear with temperature increasing.At 800 ^oC,a layer of authigenic oxide layer is formed on the worn surface,preventing directly contacting between Si₃N₄ ceramic ball and HEAs and improving wear resistance.At 800 ^oC,Al_0.2Co_1.5Cr Fe Ni_1.5Ti C_0.4 HEA has the smallest friction coefficient and its wear rate ranks only second to Al _0.2Co_1.5Cr Fe Ni_1.5Ti C HEA,showing excellent high-temperature friction and wear behaviors.