Microstructure And Properties Of In-situ TiN Reinforced AlCoCrNiTi-M(M=Fe,Cu) High Entropy Alloy Coatings By Laser Cladding

In order to upgrade the microhardness,wear resistance and corrosion resistance of TC4 alloy surface,further expand its application in the engineering field.In this study,AlCoCrNiTi(Fe,Cu)high entropy alloy coatings,TiN-reinforced AlCoCrNiTi(Fe,Cu)high entropy alloy coatings and directional array TiN-reinforced AlCoCrNiTi(Fe,Cu)high entropy alloy coatings were synthesized on the surface of TC4 alloy via laser cladding and magnetic field-assisted laser cladding,respectively.The microstructure formation mechanisms of the above three kinds of high entropy alloy coatings were systematically investigated,and the effects of different array modes of TiN on the microhardness,wear resistance and corrosion resistance of high entropy alloy coatings were analyzed.The dendritic region and interdendritic region of AlCoCrNiTi(Fe,Cu)high entropy alloy coatings were BCC solid solution phase and CoTi2 intermetallic compound phase,respectively.BCC phase with greater microhardness played a major role in improving the microhardness and wear resistance of high entropy alloy coating.The microhardness and wear resistance of AlCoCrNiTi(Fe,Cu)high entropy alloy coating were 2 times and 4 times higher than that of TC4 alloy,respectively.In 3.5wt.%NaCl solution,AlCoCrNiTi(Fe,Cu)high entropy alloy coatings had good corrosion resistance,and the self-corrosion current densities were 9.67×10-8 A/cm2 and 7.41×10-8 A/cm2,respectively,which were one order of magnitude smaller than TC4 alloy.In order to improve the microhardness,wear resistance and corrosion resistance of AlCoCrNiTi(Fe,Cu)high entropy alloy coatings,TiN-reinforced AlCoCrNiTi(Fe,Cu)high entropy alloy coatings were in-situ synthesized by laser cladding technology.The results indicated that the approximately spherical high-hardness TiN-reinforced phases were randomly distributed in high entropy alloy coatings,which increased the lattice constant of BCC phase and refined the grain size.The microhardness of AlCoCrNiTi(Fe,Cu)high entropy alloy coating increased by 33.33%and 24.36%,respectively,and the wear loss weight decreased by about 50%.Moreover,in 3.5wt.%NaCl solution,the self-corrosion current densities of TiN-AlCoCrNiTi(Fe,Cu)high entropy alloy coatings decreased to 5.85×10-8 A/cm2 and 4.23×10-8 A/cm2,respectively.In order to solve the problem that in-situ TiN was unevenly distributed in AlCoCrNiTi(Fe,Cu)high entropy alloy coatings,resulting in the uneven protection of high entropy alloy coatings.The directional array TiN-reinforced AlCoCrNiTi(Fe,Cu)high entropy alloy coatings were prepared by magnetic field-assisted laser cladding.The results indicated that the microstructure of TiN-reinforced phase was a "cross" shape of directional array and parallelled to the magnetic field direction.The maximum microhardness of TiNd-AlCoCrNiTi(Fe,Cu)high entropy alloy coatings were 2.5 times higher than that of TC4 alloy.Besides,the N-Cr and N-Co shear-resistant covalent bonds ensured the bonding strength between TiN and high entropy alloy coating,and enhanced the wear resistance and friction reduction of TiNd-AlCoCrNiTi(Fe,Cu)high entropy alloy coatings.In 3.5wt.%NaCl solution,the self-corrosion current densities of TiNd-AlCoCrNiTi(Fe,Cu)high entropy alloy coatings were reduced to 2.19×10-8 A/cm2 and 1.79×10-8 A/cm2,respectively.