Microstructure And Properties Of Laser Cladding TiMoCr Refractory High Entropy Alloy Coatings

Refractory high entropy alloy coating has the characteristics of high entropy alloy and excellent high temperature performance,which is expected to become a new type of superalloy and a new research focus in the field of materials.Based on the formation criterion of high entropy alloy,eight alloying elements ti-Mo-Cr-Nb-Al-V-Ta-W were studied in this paper.Four kinds of refractory high entropy alloy coatings,TiMoCrNb Al,TiMoCrNb V,TiMoCrNb W and TiMoCrWTa,were prepared by laser cladding technology,and the best system was selected by observing the microstructure and morphology and testing the properties.On this basis,the influence of element content on the phase,microstructure,hardness,tribological properties,oxidation resistance and corrosion resistance of the coating was studied by simultaneously changing the content of W and Ta elements,and the optimal composition of TiMoCrWTa high entropy alloy coating was optimized as TiMoCrW_0.3Ta_0.5.The evolution law of high entropy alloy coating was further studied,including the microstructure and properties after annealing at the same time and different temperatures.In addition,the high temperature performance of the coating was evaluated.1.Four refractory high-entropy alloy coatings prepared by laser cladding using high-entropy alloy formation criteria and phase diagram simulation design.All the four systems contain BCC and Laves phases,and TiMoCrNb Al and TiMoCrNb W systems contain additional FCC phases.The phase composition of cladding layer is basically consistent with the simulation calculation.The four kinds of high entropy alloy coatings all contain hard Laves phase and have high hardness and excellent wear resistance.The TiMoCrWTa coating has the highest microhardness(933.6HV_0.5)and the lowest weight loss due to constant and high temperature wear.2.Based on the optimal TiMoCrWTa system,a series of TiMoCrW_xTa_y（x=0.1,0.3,0.5,1;y=0.1,0.3,0.5,1）High entropy alloy coating.With the change of W and Ta elements,the phase in the coating does not change,and the microstructure is obviously coarsened.At the same time,microcracks and unmelted W particles occur in the coating.Among W_xTa_y coatings,W_0.3Ta_0.5coatings have more uniform microstructure,the highest microhardness(1059.1HV_0.5),and excellent wear and corrosion resistance.3.The oxidation resistance of TiMoCrW_xTa_y high entropy alloy coating was studied at800℃for 50h.The oxidation products on the coating surface are composed of CrTaO₄,Cr₂O₃,TiO₂,Ti TaO₄ and Ta₂O₅.The oxide film formed is uniform and compact,which effectively prevents the diffusion of O atoms.The W_0.3Ta_0.5 coating has the lowest oxidation weight gain of 13.4mg and the lowest self-corrosion current density of 9.41×10^-7 A·cm^-2.4.After annealing at different temperatures,the phase of W_0.3Ta_0.5coating remains BCC and Laves phase.After annealing at 800℃for 4h,W_0.3Ta_0.5 coating has a high hardness of1011.9Hv_0.5 and a wear resistance of 3.91mg,indicating that W_0.3Ta_0.5 coating has a better high-temperature softening resistance at 800℃,and the corrosion resistance is further improved.