Study Of Self-lubricating Wear-resistant Composite Coatings On Ti6Al4V By Laser Cladding

Titanium alloys have been utilized widely in various industrial fields due to theirseveral beneficial properties, such as high strength to high melting point, weight ratio, lowdensity, high corrosion resistance and biocompatibility. But it can’t be used as keytribological moving components because of its relatively lower hardness and wear resistance.Moreover, there are many tribological components working in high temperature aggressiveenvironments where liquid lubricants and greases cannot be used, demanding combination ofhigh temperature wear, oxidation, and self-lubricating. Fabricating high-temperaturewear-resistant self-lubrication coating using some advanced surface modification methodsis one of the most efficient and economic ways to solve the problem.In order to explore the new way to improve the commercial application of titanium alloy,in this paper, the NiCr/Cr3C2, NiCr/Cr3C2-WS2and NiCr/Cr3C2-CaF2are used as alloypowders preplaced on the Ti6Al4V alloy. Then the wear-resistant and self-lubricatingwear-resistant composite coatings are fabricated by laser cladding technology. Phaseconstituents and microstructures were deeply investigated by X-ray diffractomete（rXRD）,scanning electron microscope（SEM）and energy dispersive spectrometer（EDS）. Thetribological properties of the fabricated composite coatings were evaluated using aball-on-disc wear tester under dry sliding condition at ambient temperature,300℃and600℃, respectively, friction-reducing and anti-wear capabilities as well as the wearmechanisms of the composite coating and the counter-body were studied systemically.The results indicated that the γ-NiCrAlTi/TiC wear resistant composite coatingcontained α-Ti, hard TiC carbide, γ-NiCrAlTi solid solution and mean hardness value ofthe laser cladding composite coating is about1100HV0.2. Theγ-NiCrAlTi/TiC+TiWC2/CrS+Ti2CS self-lubricating wear resistant composite coating hasunique microstructure consisting of α-Ti, TiC, TiWC2, γ-NiCrAlTi, Ti2CS and CrS phases.Average micro-hardness of the composite coating is1005HV0.2. The γ-NiCrAlTi/TiC/CaF2 self-lubricating wear resistant composite coating has microstructure consisting of α-Ti, TiC,γ-NiCrAlTi and small fine CaF2particles. Average micro-hardness of the compositecoating is1050HV0.2.Friction and wear test showed that due to the combined effects of high hardness TiCenhancement and γ-NiCrAlTi solid solution, the friction coefficient and wear rate of theγ-NiCrAlTi/TiC composite coating were significantly lower than the Ti6Al4V alloy atambient temperature. Laser cladding γ-NiCrAlTi/TiC composite coating has goodfriction-reducing and wear resistance at ambient temperature. From300℃to600℃,Ti6Al4V alloy occurred severe oxidation and formed TiO2which has friction-reducing andwear resistance properties.The friction coefficient and wear rate of theγ-NiCrAlTi/TiC+TiWC2/CrS+Ti2CS composite coating were decreased from ambienttemperature to600℃to different extent with respect to the Ti6Al4V substrate. Theimprovement in wear resistance is believed to be the combined effects of the γ-NiCrAlTisolid solution, the dominating anti-wear capabilities of the reinforced hard TiC and TiWC2carbides and the self-lubricating Ti2CS and CrS sulfides. From ambient temperature to600℃, the friction coefficient and wear rate of the γ-NiCrAlTi/TiC/CaF2composite coatingwere reduced to different extent with respect to the Ti6Al4V substrate. The improvement inwear resistance is believed to be the combined effects of the γ-NiCrAlTi solid solution, thedominating anti-wear capabilities of the reinforced TiC carbides and the self-lubricatingproperties of CaF2. The γ-NiCrAlTi/TiC/CaF2composite coating possesses excellentself-lubricating and wear resistance properties. Meanwhile, the wear of counter-body Si3N4decreased to different extent.