Study On The Microstructure And Properties Of WMoTaNbV_x Refractory High-entropy Alloy Coatings By Laser Cladding

Nickel-based high-temperature alloys are widely used in aerospace and marine industries,but due to the harsh working environment and high service requirements they are nearing their limits and cannot meet the needs of equipment upgrades.The WMo Ta Nb series of refractory high entropy alloys have excellent mechanical properties,resistance to high temperature oxidation and corrosion resistance,so their preparation as coatings is expected to further improve the overall performance of nickel-based high temperature alloys.In this paper,the WMo Ta Nb V_x refractory high-entropy alloy coating was prepared by laser melting on Inconel 718 nickel-based alloy substrate,establishing the optimal process parameters,studying the influence of V elements and rare earth oxide particles on the structure and properties of the organization,revealing the strengthening mechanism of the second phase particles on the mechanical properties,corrosion resistance and high temperature properties of the coating,and realizing the high-performance laser melting refractory high-entropy alloy coating.The results show that:（1）The optimum process combination for the preparation of WMo Ta Nb V_xrefractory high-entropy alloy coatings on the surface of Inconel 718 nickel-based alloy using laser cladding is a laser power of 1000 W and a scanning speed of 900 mm/min.The prepared coatings are mainly composed of equiaxed,dendritic,columnar and intergranular crystals,and the distribution of elements shows that there is mutual diffusion and dilution of elements between the coating and the substrate.The element distribution shows that there is a diffusion and dilution of elements between the coating and the substrate,indicating that the coating and the substrate are well bonded.The physical phase examination shows that the coating is mainly composed of BCC phase,Fe containing phase and Laves eutectic phase.After the addition of the rare earth oxide Y₂O₃,the grain size of the coating alloy gradually becomes smaller and most of the Y₂O₃ will float up and agglomerate on the surface of the coating due to its low density due to the presence of a short liquid micro-melt pool during the cladding process.（2）Due to the presence of solid solution strengthening and fine grain strengthening effects,the microhardness and high temperature wear resistance of the coating increases as the Y₂O₃ content increases,with a maximum hardness of 1349.8 HV and a minimum wear rate of 0.37×10^-5 mm³/Nm at 800°C.The addition of refractory elements V and rare earth oxides Y₂O₃ leads to an increase in the corrosion interface and thus reduces the corrosion resistance of the coating.Therefore,the WMo Ta Nb coating showed the best corrosion resistance with a corrosion potential and corrosion current density of-0.1439V and 2.976×10^-8 A/cm².（3）The thickness of the oxide film gradually increased with the increase of temperature and time during the oxidation process.In the experiment of oxidation at 1000℃for 100 h,the generated substances such as V₂O₅ and Mo O₃ volatilised easily at high temperature leading to the oxide film becoming loose and porous sponge-like,followed by the appearance of small holes at the oxidation interface due to the difference in the diffusion rate of internal and external ions during the oxidation reaction.The WMo Ta Nb V coating with 2 wt.%Y₂O₃ exhibited the best oxidation resistance due to the coating of Y₂O₃ on the surface and the high eutectic content,with oxidation rates of 0.06,0.15 and0.31 mg²/cm⁴h at 600°C,800°C and 1000°C,respectively.