Preparation And Properties Of TiZrMoSn_0.8Hf_0.2 High Entropy Alloys

High entropy alloy,a new type of alloy material with different design concept from traditional alloys,has many excellent properties that traditional alloys do not have.In clinic,the comprehensive mechanical properties of medical alloys need to be improved.Therefore,a kind of biomedical high entropy alloy material with low modulus,high strength,excellent comprehensive mechanical properties and good corrosion resistance can be obtained through the design concept of high entropy alloy and other methods such as alloying or heat treatment to meet the needs of people.In this paper,the as-cast TiZrMoSn_0.8Hf_0.2high entropy alloy was prepared by vacuum non-consumable arc melting furnace.At the same time,the alloy was annealed by heat treatment process.The phase composition,microstructure,hardness,high temperature oxidation resistance,wear resistance and corrosion resistance of the alloy in as-cast and annealed state were studied and explored.A biomedical high entropy alloy with excellent microstructure properties was obtained.It is found that the phase structure of the as-cast and annealed TiZrMoSn_0.8Hf_0.2high entropy alloy is composed of BCC phase,Hf₅Sn₃phase and intermetallic compound Ti Zr.The as-cast microstructure is typical dendritic crystal and cellular crystal,and there is composition segregation,and the microhardness is up to651HV.The microstructure of the annealed alloy is refined,the composition segregation is relieved,and the microhardness is increased compared with that of the as-cast alloy,and the hardness is the highest at 600℃,reaching 712HV.Compared with the as-cast alloy,the annealed TiZrMoSn_0.8Hf_0.2high-entropy alloy in Ringer corrosion solution has a corrected corrosion potential,smaller corrosion current density,and better corrosion resistance than the as-cast alloy.The corrosion resistance of the alloy at 900℃is the best,the corrosion potential is-0.56V,the corrosion current density is 4.88×10^-8A/cm².In the corrosion solution of3.5wt.%Na Cl,the corrosion resistance of the alloy at 700℃becomes poor except for the improvement of the corrosion resistance.The corrosion process of the alloy at700℃is a passivation-corrosion-passivation cycle.After cyclic oxidation at 600℃,700℃and 800℃for 25h,the surface of the as-cast TiZrMoSn_0.8Hf_0.2high entropy alloy all forms an oxide film.The main composition of the oxide film is SnO₂and Hf（Mo O₄）₂.At 600℃and 700℃,the oxide film is dense and thin,and its oxidation resistance is good.At 800℃,the thickness of the oxide film reaches 700μm.The surface of the oxide layer is porous and porous,and the oxidation resistance of the alloy is poor.With the increase of oxidation time,the diffusion oxidation zone appears behind the oxide film,and the main composition of the oxides in this area is ZrO₂,TiO₂and HfO₂.The friction coefficient of TiZrMoSn_0.8Hf_0.2high entropy alloy after annealing at600℃～900℃is 0.8,0.2,0.5,0.6,0.8,respectively.The friction coefficient of TiZrMoSn_0.8Hf_0.2high entropy alloy is minimum at 600℃.The main wear mechanism of the alloy is adhesive wear and slight abrasive wear.At 600℃,the wear quantity is the least,and the wear size and depth of the wear mark are the best.The adhesive wear is light.