Microstructure and high temperature oxidation resistance of in-situ synthesized TiN/Ti3Al intermetallic composite coatings on Ti6Al4V alloy by laser cladding process

Abstract

High temperature anti-oxidation TiN/Ti3Al intermetallic composite coatings were fabricated with the powder and AlN powder on Ti6Al4V titanium alloy surface by 6 kW transverse-flow CO2 laser apparatus. The chemical composition, morphology and microstructure of the TiN/Ti3Al composite coatings were characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). In order to evaluate the high temperature oxidation resistance of TiN/Ti3Al coating, the isothermal oxidation test was performed in a high temperature resistance furnace at 600 °C and 800 °C, respectively. The result shows that the composite coating has a rapidly solidified fine microstructure consisting of TiN primary phase (granular-like, flake-like or dendrites), with an even distribution in Ti3Al matrix. It indicates that a physical and chemical reaction between Ti powder and AlN powder has completely occurred under the laser irradiation condition. In addition, the microhardness of the TiN/Ti3Al intermetallic composite coating is 3.4 times higher than that of the Ti6Al4V alloy substrate and reaches 844 HV0.2. The high temperature oxidation behavior test reveals that the high temperature oxidation resistance of TiN/Ti3Al composite coating is much better than that of titanium alloy substrate. The excellent high temperature oxidation resistance of TiN/Ti3Al intermetallic composite coating is attributed to the formation of reinforced phases TiN, Al2O3 and TiO2. The laser cladding TiN/Ti3Al intermetallic composite coating is anticipated to be a promising high temperature oxidation resistance coating for Ti6Al4V alloy.