Research On Tribological Properties Of TiAl Matrix Self-lubricating Composites With Ag/graphene

Research on lubrication theory and lubrication material under severe conditions is a very valuable subject in the fields of material science and tribology.Many experiments and applied researches on tribology and lubrication material,which occur in the conditions of high-temperature and heavy-load,have been done.However,previous researches are mainly focused on explanations of experimental phenomena.Understandings and expressions on tribological behavior are still not full-scale enough.Hence,the design and application of lubrication material are only based on experiments.Besides,new solid lubricants with more excellent lubrication performance are always expected.In this regard,the migration of solid lubricant and the local damage of solid lubricating film are theoretically analyzed with Hamilton&Hashin model,elastic-plasticity contact theory and numerical calculation technology.Furthermore,taking TiAl matrix self-lubricating composite?TMSC?containing Ag/graphene as a research object,experimental verification and tribological properties are carried out.The conclusions are depicted as follows:According to the sliding friction characteristics of metal matrix self-lubricating composite,a model for analyzing the migration of solid lubricant was built.Then a mathematical model of calculating the thickness of solid lubricating film?SLF?using Hamilton&Hashin model and elastic-plasticity contact theory was further deduced.Taking TMSC containing Ag as a research object,the migration mechanism of solid lubricant and the effects of experimental conditions on the migration mechanisms and the thickness of SLF based on the models were explored using numerical calculation technology.Furthermore,a comparison of theoretical and experimental data was carried out to verify the reasonableness of the model.Secondly,analyzing the sliding friction characteristic of worn surface on matrix self-lubricating composite,a model for analyzing sliding friction contact was built.Then a mathematical model for calculating the surface stresses of SLF was deduced using Hamilton model.Taking TMSC containing Ag as a research object,the local damage mechanism of SLF surface and the effects of experimental conditions on the surface stress distribution and the local damage mechanisms of SLF based on models were explored using the numerical calculation technology.Furthermore,a comparison of theoretical and experimental data was carried out to verify the reasonableness of the model.In order to systematically verify the reasonableness of the previous theoretical analysis at the reactor scale,tribological properties of TMSC containing Ag were investigated under different experimental conditions,such as concentration of lubricant,normal load and counterface material.The morphologies of worn surfaces and the characteristics of SLF were characterized using advanced test methods.The effects of experimental conditions on friction coefficients and wear rates were obtained.The experimental results and phenomena further verified the reasonableness of theoretical analysis in the second and third chapter.Multilayer graphene?MLG?possessed high strength,high thermal conductivity,low friction coefficient and unique two-dimensional lamellar structure.Thus,the room temperature tribological properties of TMSC with MLG and the comparison of lubrication properties for MLG and WS₂ were investigated.Moreover,their lubrication,anti-friction and anti-wear mechanisms were explored.The results suggested that MLG not only increased the strength but also improved the self-lubrication properties,which had a better lubrication property than WS₂ under same experimental conditions.TMSC with 3⁴wt%MLG possessed high hard,low friction coefficient and low wear rate.High temperature wear tests of TMSC with MLG suggested that MLG possessed excellent lubricating property within 550°C and lost lubricating property due to high-temperature oxidation above 600°C.On this basis,TMSC containing MLG and Ti₃SiC₂ with excellent tribological properties from room temperature to 800°C were studied,whose friction coefficients and wear rates respectively maintained about0.34⁰.36 and 0.85¹.12×10^-4 mm³ N^-1m^-1.Herein,Ti₃SiC₂ was oxidized to form TiO₂&SiO₂ with high temperature lubrication property,which was responsible for the excellent tribological properties at elevated temperatures.