The Research On TiN/Co Composite Coatings On Inconel 718 Superalloy By Laser Cladding Technology

The aero-engine is a prized possession in the industry,with its turbine blades and other moving parts playing a crucial role.As the demands for engine performance continue to rise,the need for extended part life and reliability has become increasingly important.Inconel 718 superalloy is popular for turbine blades and other moving parts due to its stable chemical composition,excellent corrosion resistance,and mechanical properties.However,prolonged exposure to high temperature,pressure,and high-speed operations can cause low hardness and wear resistance,leading to wear loss.Therefore,it is important to improve its wear resistance and anti-friction performance to extend its service life.A wear-resistant composite coating can be applied to the surface to combat this issue.In this study,we utilized pure Co metal powder,known for its toughness,and TiN powder,renowned for its superior wear resistance as raw materials.We designed four powder systems consisting of pure Co,Co-2 wt.%TiN,Co-4 wt.%TiN,and Co-6 wt.%TiN.These systems were fused onto Inconel 718 substrate using laser melting and simultaneous powder feeding technique to produce wear-resistant composite coatings.The tribological properties and microhardness of the substrate and composite coatings were tested at room temperature and 600℃,while their oxidation characteristics were explored at 800℃.The XRD,SEM,and EDS were utilized to characterize the physical phase,microstructure,surface wear,and oxidation morphologies of the composite coatings.Furthermore,we conducted an in-depth analysis of the wear mechanism and oxidation behavior of the composite coatings in the wide temperature range.The findings of our study indicate that the coatings exhibited excellent metallurgical bonding with the substrate.The pure Co coating comprised y-Co and(Fe,Ni)solid solution,intermetallic compound Cr3Ni2 and CrCo,while the composite coatings with TiN powder added showed diffraction peaks of TiN and CoTi2.The microhardness test results revealed that the four coatings had values of 310.4 HV0.5,341.7 HV0.5,380 HV0.5,and 420.3 HV0.5,respectively.The coatings exhibited significant improvements in hardness compared to the substrate(269.3 HV0.5),which can be attributed to fine grain strengthening due to laser melting,solid solution strengthening from y-Co and(Fe,Ni)solid solution,and the presence of hard phases like TiN that contribute to diffusion strengthening at grain boundaries.Upon exploring the antioxidant performance of the four composite coatings at 800℃,it was observed that the antioxidant capacity of the coatings was not particularly strong.The oxidation kinetic curves indicated an increase in weight gain per unit area of the substrate and the coatings,with values of 56.54,88.21,110.65,76.25,and 66.156 mg/cm2.The surface of the substrate exhibited dense Cr2O3,Fe2O3 and NiCr2O4 oxides,while the coating surface showcased TiO2 and CoO.However,the oxidized coating surface showed clear signs of flaking,indicating poor oxidation resistance.At room temperature,the substrate and four coatings exhibited average friction coefficients and wear rates of 0.711,0.693,0.548,0.613,0.641 and 9.73 × 10-5,6.94 ×10-5,2.13 × 10-5,1.58 × 10-5,1.48 × 10-5 mm3/(N·m),respectively.The composite coatings demonstrated superior wear-resistant and friction reduction performance.The Co-2 wt.%TiN coating exhibited the most significant improvement in coating friction reduction performance due to the synergistic effect of hard phase and a small amount of oxide,and the coefficient of friction is reduced by 22.9%compared with the substrate.The wear mechanism is adhesive wear and micro-oxidation wear.The Co-6 wt.%TiN composite coating demonstrated the lowest wear rate,with an 84%decrease compared to the substrate,indicating the best wear resistance.The main wear mechanisms were micro-oxidation wear and micro-abrasive wear.At high temperature,the composite coatings and substrate exhibited average friction coefficients and wear rates of 0.723,0.553,0.522,0.474,0.574 and 9.61 × 10-5,8.37 × 10-5,1.79 × 10-5,9.88 × 10-6,7.82 × 10-6 mm3/(N·m),respectively.The Co-4wt.%TiN composite coating demonstrated the lowest friction coefficient at high temperature,which is reduced by 34.4%compared to the substrate,and its wear mechanisms were attributed to oxidation wear and fatigue wear.The Co-6wt.%TiN composite coating demonstrated the best wear resistance,with 11 times increase compared to the substrate.The main wear mechanisms were oxidation wear,adhesive wear,and micro-abrasive wear.