Effect Of Strengthening Method On Mechanical Properties And Tribological Properties Of Ni-based Self-lubricating Composites

With the rapid development of high-tech industries including aerospace engineering,energy power,etc,there are constantly increasing requirements for the strength and tribological properties of materials in service under extreme conditions.Especially for high temperature machinery represented by advanced engines,because of its harsh working environment,has put forward higher and higher requirements for wear-resistant materials with high strength at high temperature due to its harsh working environment.In this thesis,series of Ni-based composites materials were fabricated by powder metallurgy method?high-energy ball milling and vacuum hot pressing sintering?.The effects of metal oxides and in-situ formation of refractory carbides as a reinforcing phase and wear resistance on the microstructure,mechanical properties,and tribological properties of Ni-based composites were studied.The main results are as follows:The NiCrMoAlAg alloy matrix was compounded with Al₂O₃ to prepare NiCrMoAlAg-Al₂O₃ composites.The microstructure,mechanical properties and tribological properties in wide temperature range of the composite were investigated.The deformation fracture mechanism and wear mechanism were analyzed.The results show that the addition of Al₂O₃ improves the density,hardness,and tensile and compression properties of the material from room temperature to 1000°C.The fracture mechanism of NiCrMoAlAg-Al₂O₃ composite at different temperatures is microporous aggregation and intergranular fracture.At room temperature,NiCrMoAlAg alloys and NiCrMoAlAg-Al₂O₃ composites have low wear rates but high friction coefficients.At 200?,the wear rate of NiCrMoAlAg-Al₂O₃ composite is an order of magnitude higher than that of NiCrMoAlAg alloy,which may be caused by the homogeneous wear between the composite and the dual ball.The two materials formed a lubricating film composed of NiO,Ag₂MoO₄ and other lubricants during the high-temperature friction process to reduce the friction coefficient and wear rate of the materials.The vacuum pressureless sintering method is used to prepare Ti₂AlC powder.Ni/Ti₂AlC composites with different Ti₂AlC contents were prepared by high-energy ball milling and vacuum hot-pressing sintering technology.The microstructure,mechanical properties and tribological properties at room temperature and 800?of the composite materials were studied.The results show that for Ni-10mol.%Ti₂AlC composites,the phases formed during the sintering process are Ni-based solid solution,TiC_x and Ni₃?Al,Ti?.For Ni-50mol.%Ti₂AlC composites,the reaction products are mainly composed of TiC_x,NiAl,Ti₃NiAl₂C and Ni₂AlTi,and a small amount of Ti₃AlC₂.For Ni-64mol.%Ti₂AlC composite,it is mainly composed of TiC_x,Ti₃NiAl₂C and NiAl,and a small amount of Ti₃AlC₂ and Ti₂AlC.The Ni/Ti₂AlC composites with different Ti₂AlC contents show excellent friction and wear properties at 800?,and the worn surfaces of the composites are covered with oxide film.With the increase of Ti₂AlC content,the film area of the worn surface increases.The good friction and wear performance of composites at high temperatures mainly depends on the oxide film on the worn surface.