Structure And Properties Of CrNbNiTiV High Entropy Alloy

High entropy alloys are a kind of alloy with simple structure,which are prepared by melting and sintering with 5?13 elements mixed in equal or near equal molar ratio.The alloys have excellent performance,for example,high hardness,high strength,corrosion resistance,good high temperature oxidation resistance and thermal stability,and have broad application prospects and research significance.In this paper,CrNiTiMoV high entropy alloys are prepared by vacuum arc melting and annealed.The phase structure,microstructure,composition,hardness,corrosion resistance and high temperature oxidation resistance of the as cast alloy are investigated by X-ray diffraction,scanning electron microscope,energy dispersive spectrometer,microhardness tester,electrochemical workstation and high temperature carbon rod resistance furnace.The effect of annealing temperature on the structure and properties of the alloy are discussed and analyzed.The results show that as-cast and annealed CrNiTiMoV high-entropy alloys are composed of BCC solid solution,NiTi phase and Ti-rich phase,and annealing has little effect on the phase composition.As the annealed temperature increases,the dendritic structure of the BCC phase grows,and the precipitation of the Ti-rich phase increases.When annealed at 900?,the Ti-rich phase re-dissolves back to the interdendritic region.The hardness of the CrNiTiMoV high entropy alloys are increased by annealing,and the maximum hardness is 684 HV after annealing at 800?.The hardness is affected by solution strengthening and precipitation strengthening of Ti rich phase.CrNiTiMoV high-entropy alloys show good thermal stability and softening resistance.Polarization tests of as cast CrNiTiMoV high entropy alloy in 2%,10%and 15%HNO₃solution show that the higher the nitric acid concentration is,the lower the self corrosion tendency is,the higher the corrosion rate is,and the wider the corrosion cracks appear along the grain boundary.There are no obvious corrosion pits in the dendritic BCC phase,and the NiTi phase between the dendrites is preferentially corroded,and obvious pitting corrosion pits appear.After annealing,the CrNiTiMoV alloy has fewer defects and a more uniform structure.In a 2%HNO₃solution,annealing at 600? improves the corrosion resistance of the alloy,but as the annealing temperature increases,the precipitation of Ti-rich phases reduces the corrosion resistance of the alloy.In 10%HNO₃solution,annealing treatment improves the pitting corrosion resistance of CrNiTiMoV high entropy alloy.In 15%HNO₃solution,the corrosion resistance of the alloy is improved after annealing at 900?.As cast and annealed CrNiTiMoV high entropy alloys have low oxidation rate at500?and 600?,and the formed oxide film has good protection and high temperature oxidation resistance.The oxidation products oxidized at 700?have no protection and poor high temperature oxidation resistance.When the alloy is oxidized at 500?,the oxidation weight gain of the alloy annealed at 600?is smaller than that of the as cast alloy,which improves the oxidation resistance.The oxidation resistance of the alloy decreases with the increase of annealing temperature.When the alloy is oxidized at600?,the high temperature oxidation resistance of the alloy is improved by annealing.When the alloy is oxidized at 700?,cracks,oxide layer cracking and even spalling appear in the annealed alloy,resulting in serious oxidation.Annealing treatment has no effect on the formation of oxide.The as-cast and annealed CrNiTiMoV high-entropy alloys produce the same oxides during oxidation.When oxidized at 500? TiO₂is formed,when oxidized at 600? TiO₂and VO₂are formed,and when oxidized at 700?TiO₂,CrVO₃and NiMoO₄ are formed.