Tribological Properties Of NiAl Based Self-lubrication Coatings Prepared By Atmospheric Plasma Spraying

Self-lubricating composite materials are composed by two or more constituents,and have unique properties compared with other solid lubricating materials.It can be used in special working conditions,such as highly temperature,highly vacuum,strongly radiation and highly load,it can resolve the friction and wear of mechanical equipment in aerospace,chemical,metallurgy.As a result,self-lubrication composite materials obtained a lot of research attention.One of the effective methods to get lubrication at wide temperature range is rational utilization of different lubricants.In this paper,the self-lubricating composite coatings was prepared by plasma spraying technique.In those coatings,the lubrication at high temperature can be obtained by the fluorides or silver metal oxides.Ag acts as a low temperature lubricant,Cr2O3 acts as hardening phase,and NiAl acts as the main phase.Its tribological properties at the temperature range from 20? to 750? were investigated.The effect of temperature,constituent and content on the tribological properties was studied.The structure,morphology,element composition and its distribution on the surface of the composite coating and wear track were then analyzed by means of XRD,SEM,EDS and Raman.The friction and lubrication behaviors of coatings under different temperature was also discussed.This dissertation used the orthogonal test to investigate the effects of spraying parameters such as spraying distance,spraying current,and argon flow rate on the coating quality to determine the optimal spraying parameters.In NiAl-Mo-Ag-BaF2/CaF2-Cr2O3 composite coating,the Cr2O3 improved the micro-hardness of coatings,the wear rate decreased an order of magnitude(10-4mm3/Nm to 10-5mm3/Nm),those coatings has lowest wear rate at room temperature;At high temperature,the wear track product silver molybdate with low melting point by tribo-chemical reaction,and its tribological performance of 750 ? was improved.Increased the contents of lubricant Ag(5wt.%-10wt.%),the friction coefficient and wear rate increased above 400 ?;added 5wt.%eutectic fluoride,the friction coefficient and wear rate of coatings reduced,when get 10wt.%,the coating mechanics performance was declined,and the friction coefficient and wear rate both increased;The 65%NiAl-5%Mo-5%Ag-5%BaF2/CaF2-20%Cr2O3 composite coating showed better tribological properties at various temperature.In NiAl-Ta-Ag-Cr2O3 composite coating,those coatings has highly hardness and lubrication,the wear rate at room temperature was extremely low(10-7mm3/Nm orders of magnitude);At 750?,the AgTaO3 was product by tribo-chemical reaction,it was conducive to formed dense oxide film,reduced the friction coefficient and wear rate at high temperature;When the content of Ta from 5wt.%increased to 10wt.%,the friction coefficient increased above 400 ?;the friction coefficient and wear rate reduced at all the temperature when the Ag mass fraction increased to 10%,but when Ag content was 15wt.%,the friction coefficient and wear rate increased;65%NiAl-5%Ta-10%Ag-20%Cr2O3 coating keep a lower friction coefficient and wear rate in various temperature and shows better tribological performance...