| Laser cladding,a rapid melting and rapid-equilibrium solidification process,leads to high residual stress and microstructure instability in the coatings.There will be concentration of stress and micro-cracks prone to exist in coating,when coating is under the induction of external force,which will restrict the industrial application of the coating.Heat treatment,an efficient method,can adjust microstructure and relieve residual stress of laser clad self-lubricating anti-wear coatings to achieve the hypothetical properties and improve the service life of coating.In this paper,the laser clad Ti-TiC-WS2 self-lubricating anti-wear composite coating was prepared on TA2 titanium alloy,and coatings were heat treated with different time and temperature.Effects of heat treatment with different time and temperature on the microstructure and mechanical properties of laser clad Ti matrix self-lubricating anti-wear composite coatings were investigated systematically.Results indicated that the Ti matrix self-lubricating anti-wear composite coatings fabricated by laser clad on TA2 titanium alloy achieved metallurgical bonding to the substrate and free from holes and cracks.The main phase composition of as-clad coating and the coating with heat treatment under 500 ? for 1 h and 2 h were all composed of a-Ti solid solution,reinforced phases of(Ti,W)C1-x and TiC and lubricant phases of Ti2SC and TiS.The microhardness of coatings with heat treatment for 1 h and 2 h(1143.3 HV0.5 and 1162.7 HV0.5)have been increased to a certain extent,compared with the coating without heat treatment(1049.8 HV0.5).Under sliding condition,the coefficient of friction and wear rate of coatings with heat treatment for 1 h and 2 h are 0.29 and 6.66×100-5 mm3· N-1·m-1,0.29 and 5.65×10-5mm3·N-1·m-1,respectively.Compared with the coating without heat treatment(0.32 and 18.92×10-5 mm3·N-1·m-1),those coatings with heat treatment for 1 h and 2 h present excellent anti-wear and friction reduction properties and the wear mechanism of coatings are all slightly abrasive wear,the wear mechanism without heat treatment are plastic deformation and adhesive wear.Under fretting condition,coatings with heat treatment for 1 h and 2 h presented the superb fretting wear resistance,the wear mechanism of coatings are adhesive wear and abrasive wear.The composite coatings were heated at 300 ?,500 ? and 700 ? for 1 h to study the effects of temperature of heat treatment on microstructure and mechanical properties of coatings.Effects of heat treatment at 300 ? on the phase composition of coating were negligible,but the reinforced phase of(Ti,W)C1-x and self-lubricating phase of Ti2SC in coatings with heat treatment at 500 ? and 700 ? were separated out.The microhardness of coating with heat treatment at 300 ? decreased to 980.7 HV0.5,and the microhardness of coating with heat treatment at 700 ? have the maximal microhardness(1190.7 HV0.5).Under sliding condition,the coefficient of friction and wear rate of coatings with heat treatment at 300 ?,500 ? 700 ? were 0.30 and 16.74×10-5 mm3·N-1·m-1,0.29 and 6.66×10-5 mm3·N-1·m-1,0.28 and 4.02×10-5mm3·N-1·m-1.Due to the decreasing of microhardness,the wear resistance of coating heat treated at 300 ? has not improved drastically.The coating with heat treatment at 700 ? presented superb self-lubricating anti-wear properties and the wear mechanism is mainly abrasive wear.Under fretting condition,the coating with heat treatment at 700 ? also exhibited outstanding fretting wear resistance and the wear mechanism are mainly adhesive wear and abrasive wear. |
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