Preparation And Tribological Properties Of NiCrW-Based Superalloy Self-Lubricating Composites

Because the mechanical parts in metallurgy work in harsh environments such as high temperature,high speed and high heavy load for a long time,there is an urgent need to develop new materials with both good mechanical properties and tribological properties.In this paper,using nickel-based superalloy as the matrix and adding different solid lubricants MoS₂,Ag and V₂O₅,NiCrW-based self-lubricating composites were prepared by powder metallurgy.The T1000 high temperature friction and wear test equipment was used to study the friction and wear performance of the nickel-based composites between room temperature and 600?.Metallographic microscope,X-ray diffractometer,scanning electron microscope,energy dispersive spectrometer and laser Raman spectrometer were used to analyze the composition and structure of the materials surface before and after the friction and wear test.The friction-wear and self-lubricating mechanism of self-lubricating composites in a wide temperature range are systematically studied.The main results are as follows:1.Using MoS₂ as a solid lubricant and NiCrW alloy as a matrix,NiCrW/MoS₂self-lubricating composites were prepared by powder metallurgy.As the MoS₂ increases,the density of the composite decreases and the porosity increases,while the hardness increases first and then decreases.During the sintering of the composites,the lubricating phase MoS₂ partially were decomposed to generate CrS.The tribological properties of the composites containing10wt.%MoS₂ are the best at various temperatures,and the friction coefficient and wear rate are within the range of 0.36-0.55 and?4.5-8.1?×10^-5mm³·N^-1m^-1.At room temperature and 300?,MoS₂ provides the main anti-friction properties,while at 600?high temperature,the main lubricating phase is CrS and the metal oxides such as NiO and MoO₃.2.NiCrW/MoS₂/Ag self-lubricating composites were prepared by using MoS₂ and Ag as solid lubricants and NiCrW alloy as the matrix by cold-press sintering.The density of the composite decreases with the addition of MoS₂ and increases with the increase of Ag content.The porosity and hardness increase with the addition of MoS₂ and decrease with the increase of Ag content.From room temperature to 600?,the composite of 8wt.%MoS₂ and 10wt.%Ag respectively has a lower friction coefficient of 0.34-0.52 and a lower wear rate?3.8-6.0?×10^-5mm³·N^-1m^-1,which has the best tribological properties.At room temperature and 300?,the low friction coefficient of the composite is the result of the synergistic lubrication effect of MoS₂and Ag.At 600?,the main lubricating phases are silver molybdate?AgMo_xO_y?,CrS and a small amount of NiO generated during the friction chemical reaction during the wear process,which greatly reduce the friction coefficients of the composites at high temperature.Therefore,the synergistic lubrication effect of the solid lubricant MoS₂ and Ag makes the nickel-based self-lubricating composites have a better friction and wear performance from room temperature to high temperature.3.Using MoS₂ and Ag as room-temperature to medium-temperature solid lubricants,V₂O₅as high-temperature solid lubricants,and NiCrW alloy as the matrix,NiCrW/MoS₂/Ag/V₂O₅self-lubricating composites were prepared by powder metallurgy cold-press sintering process.As the increasing of V₂O₅ content,the density of the composite decreases and the porosity increases,while the hardness increases first and then decreases.The composite containing 6wt.%V₂O₅ has the highest hardness.When the solid lubricants with the content of 8wt.%MoS₂,10wt.%Ag and6wt.%V₂O₅ are added,the composite have better friction and wear performances at various temperatures,especially the friction coefficient is only 0.22,the wear rate is 4.5×10^-5mm³·N^-1m^-11 at 600?.At room temperature and 300?,MoS₂ and Ag play the main lubricating function.At the high temperature of 600?,the anti-friction properties of MoS₂ and Ag fail,while silver molybdate?AgMo_x O_y?,V₂O₅ and a small amount of CrS play a major lubricating role under the action of tribochemistry.