Research On CoCrFeNbNi High Entropy Alloys Coating With Anti-oxidation And Wear-resistance By Laser Cladding

The gun barrel is subjected to extreme conditions such as high-temperature gunpowder erosion,ablation,oxidation,and projectile wear.The existing hard chromium electroplating technology is difficult to meet the demand,and the barrel components fail prematurely.The high entropy alloys(HEAs)coating is expected to be applied to the inner protection of the barrel due to its unique design concept and stable performance.In this study,CoCrFeNbNi eutectic(HEAs)coatings composed of rough FCC and strength Laves phase were prepared.The function of laser process parameters on coating quality were studied and optimized.The influence of Cr,Si,C and Ce in the coatings on oxidation in N2-44CO2-6H2O(vol.%)mixture gas and wear under 100N and 1 m/s in 800? were discussed.The main work is as follows:The functional relationship between the optimization target(dilution rate,residual stress)and the laser cladding process parameters(laser power,scanning speed,defocus amount)was established by response surface method and optimized by using the multi-objective particle swarm algorithm.The cladding coating with dilution rate(11.19%)and residual stress(172.6 MPa)by optimized parameters(power 800 W,scan speed 430 mm/min,defocus-25 mm).As the Cr increased in the CoCrxFeNb0.5Ni(x=0.5?2)HEAs coating,the complete eutectic structure transforms to incomplete eutectic structure,and Cr atoms can be dissolved into the FCC phase.During the high temperature oxidation,the oxidation of the coating is mainly the selective oxidation of the Cr and Nb.The oxidation rate of Laves inhibited by the the protective Cr2O3 oxide films.The oxidation of CoCr2FeNb0.5Ni is reduced by 57%compared to CoCr0.FeNb0.5Ni.The Si in CoCr2FeNb0.5NiSi0.2 is mainly to improve the compactness of the crystal structure size of the Laves phase.In the later stage of high temperature oxidation,the oxidation of Si in the Laves phase replace the Nb,producing a more stable(Cr,Si)Ox at the interface,and inhibiting internal diffusion of oxygen.With more addition of Si,the metal silicide is precipitated during coating,resulting in an increasing of brittleness and defects of the coating.The CoCr2FeNb0.5NiSiO2 has optimal toughness and high temperature antioxidant.The situ MC were precipitated by the diffusion of Nb and C.The hardness of CoCr2FeNb0.5NiSi0.2C0.1 is 850 HV0.3.As the C content continues increasing,the content of the Laves phase is reduced by increased of the MC particles.At the temp-erature below 400?,the hardness is a decisive factor of the coating wear resistance.As the temperature continues to increase,the surface of the coating produces a protective oxide film,the oxide film and the hardness determine the wear resistance of the coating.CoCr2FeNb0.5NiSi0.2C0.1 has the best wear resistance.With the addition of CeO2,the adsorption of Ce during the preparation process can effectively inhibit the growth of the laminate structure and refine the microstructure.Since the active element effect of Ce causes the short-range diffusion speed of Cr ions,the blade and fine-grain Cr2O3 generated in mixture gas transform to single fine-grain Cr2O3.The compactness,self-healing and bonding force of the oxide film improved by the Ce addition.The optimized high entropy alloy coating is CoCr2FeNb0.5NiSi0.2C0.1 with 1 wt.%CeO2.The wear rate of HEAs is reduced by 98%,89%,20%compared to the barrel material 32Cr2Mo1 VE,hard Cr plating,and barrel liner material Stellite 6B,respectively.The oxidation weight of HEAs coating in the simulated atmosphere at 800? is reduced by 99%,93%compared to 32Cr2Mo1VE and hard Cr plating,respectively.