Study Of Laser Clad Titanium Matrix High-temperature Self-lubricating Anti-wear Composite Coatings On TA2 Alloy

Laser cladding reinforced ceramic phase metal matrix composites on titanium alloys can enhance the hardness and wear resistance of titanium alloys.At present,that approach has been used to improve the tribological properties of of titanium alloys in many kinds of researched coatings.However,the reinforced ceramic phase metal matrix composites could present high friction coefficient under uneasy lubricated conditions,which leads to severe wear and tear of coatings and mating counterparts.Severe wear and tear is harmful to the elements’service life.Preparing composite coatings with excellent anti-wear and friction reduction properties is an effective economical,effective and reliable approach.In this paper,Ti-TiC anti-wear composite coating and Ti-TiC-WS₂ high-temperature self-lubricating anti-wear composite coatings were synthesized on TA2 alloy by laser cladding technology with Ti,TiC and WS₂ powders.The phase compositions,microstructure and microhardness of coatings were characterized by X-ray diffraction（XRD）,scanning electron microscope（SEM）,energy dispersive spectroscopy（EDS）and microhardness tester.The tribological properties of Ti-TiC and Ti-TiC-WS₂ composite coatings were evaluated using a ball-on-disc tribometer under dry sliding wear test conditions at different temperatures and loads,and the corresponding wear mechanisms were analyzed respectively.Results show that there were no crack and holes that exists in coatings and a fine metallurgical bonding was obtained between the coating and substrate.Ti-TiC anti-wear composite coating consists of a-Ti solid solution and TiC ceramic phase,and microhardness of coating was 1162 HV0.5 and about 6 times than that of substrate.Ti-TiC-WS₂ high-temperature self-lubricating anti-wear composite coating consisted of a-Ti solid solution,TiC/（Ti,W）C1-xcreinforced phase and Ti2SC/TiS self-lubricating phase,and its average microhardness was slightly lower than Ti-TiC coating with the addition of WS₂.The microhardness of Ti-TiC-WS₂ coatings was inversely proportional to the content of WS₂.When the content of WS₂ was 30.6%,Ti-TiC-WS₂ coating had the highest microhardness（1052.3 HV0.5）.It was connected with the content of TiC/（Ti,W）C1-x creinforced phase.At room temperature,the friction coefficient of Ti-TiC coating was higher than that of TA2 alloy,but its wear rate reduced by 83%than that of TA2 alloy,which indicated Ti-TiC coating had good anti-wear property.The friction reduction property of Ti-TiC-WS₂ coating had been improved due to Ti2SC/TiS self-lubricating phase.The friction coefficient of Ti-TiC-WS₂ coating decreased at first and increased later on with the increase of temperature,and the wear rate was inversely proportional to temperature.When the the content of WS₂was 34.8%,the friction coefficient of Ti-TiC-WS₂ coating was lower than substrate and other coatings in all test temperature,and the friction coefficient was 0.32,0.257 and 0.339 at room temperature,250℃ and 500 ℃ respectively.Especially at 500 ℃,the wear rate was 4.87×10-6 mm3/Nm,which was reduced by 97.7%than that of substrate.Ti-TiC-WS₂ coating present excellent high-temperature anti-wear and friction reduction properties.The friction coefficient of Ti-TiC-WS₂ coating decreased at first and increased later on with the increase of normal load,and the wear rate was proportional to normal load.The anti-wear and friction reduction properties of Ti-TiC-WS₂ coating was excellent under 3 N and 6N normal load.