Microstructure and Tribological Properties of Ti₃SiC₂ Enhanced Ni60 Composite Coatings on Ti6Al4V Alloy by Laser Cladding

Ti6Al4V alloy (TC4) has excellent comprehensive mechanical properties, so it is widely used in jet engine pressure disc, pressure boat body, water ship pump body and industrial fuselage fire wall. However, due to the poor oxidation resistance and tribological properties in high temperature environment, its application was greatly limited. Therefore, two kinds of Ti₃SiC₂/Ni60 composite coatings, i.e. 5% Ti₃SiC₂ + Ni60 (N1) and 10%Ti₃SiC₂ + Ni60 (N2)(weight fraction) were prepared by laser cladding technology on the Ti6Al4V alloy to enhance the wear resistance and friction reduction performance. The microstructure, microhardness, tribological performance and the related wear mechanisms of the composite coatings were investigated at room temperature (RT), 300 and 600 ℃ by using various characterization methods (scanning electron microscopy, X-ray diffraction, energy dispersive spectrometer). According to the results, the composite coatings were mainly composed of hard phase TiC/TiB/Ti_xNi_y, γ-Ni solid solution continuous phase and lubricating phase Ti₃SiC₂ at room temperature; however, at high temperature, dense oxide films of TiO₂ and SiO₂ with certain lubricating effect were produced. In addition, the microhardnesses of N1 and N2 composite coatings were 1 101.90HV_0.5 and 1 037.23HV_0.5, respectively, which were about three times that of the substrate (350HV_0.5), due to the effects of dispersion strengthening, solid solution strengthening, fine grain strengthening and the feature of ternary lubricating phase Ti₃SiC₂ with the dual effects of metal and ceramic. The coefficients of friction (COF) of the N1 composite coatings at room temperature, 300 and 600 ℃ were 0.39, 0.35 and 0.30, while the N2 composite coatings were 0.41, 0.45 and 0.44, which both were lower than those of substrate (0.51, 0.49, 0.47). The wear rates of N1 and N2 composite coatings at room temperature, 300 and 600 ℃ were 3.07×10⁻⁵, 1.47×10⁻⁵, 0.77×10⁻⁵ mm³/(N·m) and 1.45×10⁻⁵, 0.96×10⁻⁵, 0.62×10⁻⁵ mm³/(N·m) respectively, which both were far lower than those of the substrate 35.96×10⁻⁵, 25.99×10⁻⁵, 15.18×10⁻⁵ mm³/(N·m). It can be seen that the addition of ternary solid lubricating phase Ti₃SiC₂ improved the wear resistance and friction reduction properties of Ti6Al4V alloy in this work, rendering N1 composite coating better friction reducing performance and N2 composite coating better wear resistance. At room temperature, the wear of the substrate was mainly caused by abrasive wear, adhesive wear and plastic deformation; while abrasive wear, mild adhesive wear and plastic deformation were the main wear mechanisms of the two composite coatings. In the high temperature wear process, the surface of Ti6Al4V alloy was dominated by oxidation wear, adhesive wear, abrasive wear and mild plastic deformation. At 300 ℃, three-body abrasive wear, adhesive wear and oxidation wear were the main wear mechanisms of the two composite coatings. At 600 ℃, the main wear mechanisms were abrasive wear, adhesive wear and oxidation wear, and the plastic deformation of N2 composite coating was relatively severe.