Preparation And Wide Temperature Range Tribological Behavior Of Ni-Mo-P Based Electroless Composite Coatings

Friction and wear not only reduce the efficiency of energy transmission,but also affect the service life of key components.At present,the common lubrication method is is to add liquid lubricants,but liquid lubricants will rapidly degrade and fail under high temperature conditions.Therefore,solid lubrication is an effective means to improve high-temperature tribological properties.In the aerospace field,components are often subjected to the use process from low temperature to high temperature,so the research on solid self-lubricating coatings in a wide temperature range is of great significance.However,few researches have been carried out in this field.In this paper,electroless composite plating technology was used to prepare Ni-Mo-P coatings with different Mo contents on the surface of GH4169 superalloy by changing the concentration of sodium molybdate in the solution.Ni-Mo-P coatings with different Ce O₂contents were prepared by changing the concentration of Ce O₂in the solution,and heat treated at 400?.The composition,microstructure and properties of the coatings were analyzed by energy dispersive analyzer(EDS),scanning electron microscope(SEM),X-ray diffractometer(XRD),microhardness tester and nanoindenter.The friction and wear properties of the composite coatings at different temperatures were studied by using a high temperature friction and wear tester,and the tribological properties of the composite coatings in a wide temperature range were investigated.The effect of Mo content on the properties of Ni-Mo-P coatings was investigated.The results show that the surface of Ni-Mo-P coating is uniform and dense spherical structure.When the concentration of sodium molybdate is 0.6g/L,the Mo content of the coating is the highest,which is 5.72wt%.The hardness of the coating is related to the content of Mo and P,the higher the content of Mo or the lower the content of P,the higher the hardness of the coatings.When the concentration of sodium molybdate is 0.6g/L,the hardness of the coating is the highest,which is 645HV.The friction and wear tests at different temperatures show that the wear resistance of the coating improves with the increase of Mo content.When the concentration of sodium molybdate is 0.6g/L,the coating has the best friction and wear performance in a wide temperature range.The friction coefficients and wear rates of the coating are 0.77,0.74,0.58,0.48 and 3.29×10^-5mm~3/N·m,8.93×10^-5mm~3/N·m,5.51×10^-5mm~3/N·m,4.62×10^-5mm~3/N·m at 25?,300?,500?and 700? respectively.Ni-Mo-P/CeO₂composite coatings with different CeO₂contents were prepared by changing the concentration of Ce O₂in the bath,and then heat-treated at 400?to study the effects of Ce O₂content and heat treatment on the structure and properties of Ni-Mo-P/Ce O₂composite coatings.The results show that the spherical structure on the surface of the composite coatings are densely distributed.After the addition of Ce O₂,the crystallization degree of the composite coatings increases,the grain size increases,and the hardness of the coatings decreases to 477-590HV,but the toughness increases.After heat treatment,the spherical structure of the composite coatings becomes smaller,the crystallinity and grain size further increase,and nano-scale Ni₃P phase is generated,which increases the hardness of the composite coatings after heat treatment to 778-1148HV,and the toughness is improved.When the Ce O₂concentration is 10g/L and 15g/L,the coatings have the best wear resistance at the room temperature,the wear rate before heat treatment is 1.84×10^-5mm~3/N·m and1.91×10^-5mm~3/N·m,respectively,and the wear rate after heat treatment is1.19×10^-5mm~3/N·m and 1.04×10^-5mm~3/N·m respectively.The high temperature tribological properties of Ni-Mo-P/CeO₂composite coatings were studied.The results show that with the increase of test temperature,oxide phases such as Ni O with lubricating effect are formed in the coating,and the friction coefficient decreases.The addition of appropriate amount of Ce O₂can reduce the oxidation degree of the composite coating and improve the toughness of the coating,which is conducive to improve the wear resistance of the composite coating.Ni-Mo-P/Ce O₂composite coating with Ce O₂concentration of 10g/L has good wear resistance in a wide temperature range,the friction coefficient and the wear rates are 0.73,0.82,0.66,0.54 and 1.84×10^-5mm~3/N·m,5.54×10^-5mm~3/N·m,5.3×10^-5mm~3/N·m,9.98×10^-5mm~3/N·m respectively.The composite coatings after heat treatment at 400?have good tribological properties below 300?.With the further increase of friction test temperature,the hardness and wear resistance of the composite coating after heat treatment decrease due to the disappearance of hard phase Ni₃P and grain growth.