Structure and oxidation behavior of γ-TiAl coating produced by laser cladding on titanium alloy

In this study, a laser cladding technique was used to produce a protective TiAl-based coating on TA6Zr4DE near-alpha titanium alloy. Ti48Al2Cr2Nb powder was used as a cladding material. The microstructure of samples was characterized using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Fully lamellar microstructure consisting of γ-TiAl (fcc) and α2-Ti3Al (hcp) phases was observed in the coating. Oxidation resistance of substrate and coating was evaluated by heating the samples in an air atmosphere at 700, 800 and 900 °С during 100 h. The oxidation process of TA6Zr4DE alloy surface led to a formation of multilayered oxide films as result of repeated growth and peeling. The coated samples showed better oxidation resistance in whole temperature range compared to that of the substrate. This behavior was explained by the composition of the cladded layer. Niobium and chromium contained in the cladded powder inhibited the intensive growth of TiO2 (rutile) and contributed to the formation of a protective layer composed mainly of alumina.