Structural Design,Mechanical And Tribological Properties Of Ta-Cu/Ag Composite Coatings Prepared By Magnetron Sputtering

Aerospace,defense industry,space environment and other fields have put forward higher requirements for high-performance solid lubricating coatings in service under special conditions.In order to reduce friction and wear in a wide temperature range,tantalum is selected as the high-temperature protective coating material,and its phase structure is adjusted and the lubricity is improved by soft metal Cu/Ag doping.In this paper,Ta-Cu and Ta-Ag coatings were co-deposited by magnetron sputtering technology,the sputtering power of Cu and Ag targets was adjusted to change the alloying element content,and the mechanical and tribological properties of coatings at different temperatures were tested.In the Ta-Cu system,when the Cu content reaches 5.5 wt.%,the structure of coatings transforms from?-Ta to amorphous Ta.Meanwhile,the hardness decreases from 23.5-24.0GPa(?-Ta(Cu))to 15.8-19.3 GPa(amorphous Ta-Cu)due to changes of structure and composition.The amorphous Ta-Cu coating exhibits hard and brittle characteristics,which leads to the obvious crack propagation during the friction process.The friction coefficient and wear rate values of 0.44 and 34.8×10^-6 mm³/Nm are obtained from the Ta-24.9 wt.%Cu amorphous coating due to the precipitation of Cu at 400?,which is reduced by46%and 68%,respectively,compared with the low Cu content coating(3.3 wt.%).In the Ta-Ag system,phase transition from?-Ta(Ag)to?-Ta(Ag)occurs at the Ag content of 10.7 wt.%,as well as the hardness decreases from 22.9-24.0 GPa to 8.0-16.3 GPa.For the?-Ta(Ag)coatings,the H/E value reaches the maximum of 0.080 with 15.3 wt.%Ag addition.When the Ag content is in the range of 10.7-27.0 wt.%,the minimum friction coefficient maintains 0.23 and the wear rate is 20.0×10^-6 mm³/Nm due to the synergistic lubrication effect of the precipitation of Ag and formation of interface tribo-chemical product Ag Ta O₃ at 600?.Ta-Ag exhibits lower friction and better wear resistance than those of Ta-Cu,which is attributed to the improved toughness of?-Ta and the larger segregation rate of Ag in Ta matrix.Based on the low friction of the Ta-Ag system,a double-layer composite structure of Ag film deposited on textured Ta is designed.The tribological properties of the coating are improved by changing the texture density.Therefore,the coating with enhanced wear performance and durability is obtained when the texture density is 6%,and the wear rate is as low as 52.3×10^-6 mm³/Nm at 600?.