Microstructure And Properties Of Laser Cladding Wear-resistant Self-lubrication Composite Coatings On TiAl Alloy

γ-TiAl intermetallic alloy is considered as one of the promising elevated-temperature light-weight candidate structural material for the future aerospace industries because of its excellent combination of low density, high specific strength and stiffness, high elevated-temperature creep and fatigue properties. Promising progress in overcoming its room-temperature brittleness and elevated-temperature (>850℃) oxidation resistance has been made in the past decade. Concerns on improving its tribological properties are increasing for its successful industrial application, especially as moving tribological components. Simultaneously these moving tribological components must have the good high-temperature self-lubrication performance because its are unable to realize lubricates in addition in elevated temperature service. Fabrication of high-temperature wear-resistant self-lubrication coating on TiAl alloy surface uing some advanced surface modification methods is on of the most efficient and economic ways to solve the problem. In the paper, laser cladding with NiCr-Cr₃C₂,NiCr-Cr₃C₂+40% CaF₂ (wt.%) and NiCr-Cr₃C₂+40%CaF₂ (wt.%) (Ni-P-encapsulated) mixed powder blends, respectively was employed to produce wear-resistant self-lubrication composite metallurgical coatings on substrate of aγ-TiAl intermetallic alloy Ti-44.5Al-0.9Cr-1.1V-2.2Nb. Metal matrix composite coatings composed of oxidation-resistantγ-NiCrAlTi nickel-base solid solution ,wear-resistant Cr₇C₃,TiC reinforcing phases, self-lubrication CaF₂, were fabricated on substrate of Ti-44.5Al-0.9Cr-1.1V-2.2Nb. The thickness of the composite coatings ranges from 0.4～0.6mm and the bonding to the substrate is metallurgical, the microstructure of the laser clad composite coatings were characterized, the microhardness were tested, the room-temperature wear resistance under dry full sliding wear test conditions were evaluated; meanwhile, to cause self- lubrication CaF₂ and the substrate alloy as well as other precoating alloy has the good wettability, prevents self-lubrication CaF₂ to have the thermal decomposition and the evaporation under the high energy laser illumination, the self-lubrication CaF₂ carried on the Ni-P chemical plating encapsulated. The results show that, Microstructure of the laser clad high-temperature wear-resistant self-lubrication composite coatings with NiCr-Cr₃C₂+40%CaF₂ (Ni-P-encapsulated) powder pre-coatings consists of wear-resistant primary coarse blocky carbide Cr₇C₃ along with theγ/Cr₇C₃ eutectics,dendritic TiC and globate CaF₂. Each phases of the laser clad composite coatings is very even, average microhardness of the coating is highest, approximately is 3 times to primitive metal average microhardness . The room-temperature dry full sliding wear resistance of three the laser clad composite coatings increases, nevertheless, the laser clad composite coating that precoating NiCr-Cr₃C₂+40%CaF₂ (wt.%) (Ni-P-encapsulated)the powdered alloy to do dry full sliding wear test conditions to wear weightlessness is least, the wear resistant large scale enhancement, its average friction coefficient obviously reduces. Through chemistry encapsulated method, the self-lubrication performance of CaF₂ obtained the full effective display, wear-resisting performance of the coating enhanced greatly, and the self-lubrication CaF₂ had also proven under room temperature attrition condition also similarly can have the remarkable self lubrication effects.