Study On Design And Wear Characteristics Of Cobalt Matrix Multi-element High Temperature Anti-wear Composite Coatings

With the rapid development of modern aviation,aerospace and nuclear industries and other high-tech industries,the demand for moving parts with superb high-temperature strength and anti-wear performance under extreme working conditions is continuously increasing.At present,GH4169 nickel-based superalloy is the main material for manufacturing hot-end parts,and is widely used in aerospace and other fields.However,the alloy is severely worn at low temperature and the service temperature is limited to below650?.Coating technology can improve the tribological properties of the surface and the reliability of the motion system without affecting the function of the parts.Therefore,there is an urgent need to develop coating materials with high strength and stability,and good wear resistance in a wide temperature range(room temperature to 1000?).Co Cr Ni Fe matrix composite coatings with Y or Nb were prepared on the surface of GH4169 nickel alloy by powder metallurgy technology(P/M).The effects of Y or Nb content,temperature,load and sliding speed on the tribological properties of the coatings were systematically investigated.The stress distribution of the coatings was simulated with ANSYS,and the bonding strength of the coatings was tested with thermal shock test.The Co Cr Ni Fe matrix composite coatings strengthened by Y were prepared,and the effect of Y on the microstructure and the tribological properties of the coatings was systematically investigated.The Y element reacted with the adsorbed oxygen and other oxide impurities on the surface of the metal particles during sintering.So,the grain boundaries were purified.The formed Y₂O₃ could effectively enhance the hardness and compactness of the coatings.The friction coefficients of the coatings first decreased and then increased with the increase of temperature.However,the wear rates had an opposite trend.From 20?to600?,the wear rates of the coatings were 0.3?15 times lower than that of the substrate,and the wear rate was about 3×10^-5 mm³/N.m at 1000?.It was ascribed to the high hardness and the lubricating effect of the oxide film reinforced by Y₂O₃.The wear mechanism of the coatings was abrasive wear and slight plastic deformation at low temperature.The oxidation wear was the wear mechanism at high temperature.At 400?,the friction coefficient of the Co Cr Ni Fe matrix composite coatings strengthened by Y increased first and then decreased with the increase of the load.The increase of the sliding speed caused the gradual increase of the friction coefficient,and the wear rate showed an upward trend.The change of the tribological properties was related to the formation and distribution of the oxide lubricating layer on the surface.The wear mechanism was mainly abrasive wear at low load or low speed,and turned into a combination of abrasive wear and oxidative wear with increased load and sliding speed.Under different working conditions,the coating effectively improved the wear resistance of the substrate.The Co Cr Ni Fe matrix composite coatings with Nb were prepared,and the Nb content was optimized.The microstructure and wear resistance of the coatings were investigated.With the increase of Nb content,the hardness of the coating increased and the compactness decreased gradually.From 20?to 1000?,the friction coefficients gradually decreased with the increase of temperature and gradually reached stability;the wear rates first increased and then decreased with the increase of temperature,within the range of 0.85?7.12×10^-5mm³/N.m.The dispersed Ni₃Nb particles improved the hardness and wear resistance of the coatings.The composite coating with 5.0 wt.%Nb showed the optimal friction coefficient and wear rate in a wide temperature range.The wear mechanism was similar to that of the coatings strengthened by Y,but the coatings with Nb exhibited better tribological properties at high temperature compared to the coatings with Y.ANSYS finite element software and APDL programming language were used to build a simplified model of the cooling and high-temperature friction process of the coatings,and the deformation and stress field of the coatings were subsequently analyzed.The results showed that during cooling,the coating edge expanded and deformed,and the center appeared to warp upward;as the thickness of the coating increased,the displacement and residual stress increased.Thermal shock test was used to characterize the bonding strength.After 25 thermal cycles,the coatings retained good condition without peeling off or other obvious damages,and adhered firmly to the substrate.The bonding strength of the Y-containing coatings was better than that of the Nb-containing coatings.The experimental results were consistent with the simulation analysis.