High-temperature oxidation behaviour of laser in situ synthesised Ti-Al-Cr-Nb alloy coating on Ti-6Al-4V

Ti3Al alloy coating doped with Cr and Nb was designed and synthesized in situ on a Ti-6Al-4V substrate using laser technology. Cracking of the coating was reduced by the addition of a certain amount of elemental Cr and Nb. Isothermal oxidation behavior of the coating was investigated. Oxidation kinetic curves of coatings followed the parabolic as a whole and linear parabolic laws at 700 °C and 800 °C for 240 hours, respectively. The oxide scale of the coating remained dense and complete throughout the oxidation stage, which was composed of a mixture of Al2O3 and TiO2 in the outermost layer, Al2O3 rich in the secondary external layer, and Al2O3 and TiO2 alternating layers in the inner layer. The addition of elemental Nb can enhance the oxidation resistance by reducing the oxygen-vacancy concentration. Combined with thermodynamic and kinetic factors, the oxidation process and mechanism of coatings were analyzed and discussed .