Ti(Al,O)/Al2O3 based composite powders with three different compositions were produced by high energy milling, sintering and grounding. High velocity oxy-fuel (HVOF) spraying was used to coat these powders onto Ti-6Al-4V alloy samples. High temperature oxidation and hot corrosion behaviour of the coatings was studied in dry air and Na2SO4 + NaCl vapour, respectively. The results showed that Ti(Al,O)/Al2O3 coatings have a much improved oxidation and hot corrosion resistance compared to the substrate Ti-6Al-4V alloy. The oxide formed on the surface of the coatings after high temperature exposure is composed of a mixture of Al2O3 and TiO2. The oxide scales have excellent adhesion to the coatings, showing superior scale spallation resistance. Microstructural analysis suggested that the Al2O3 particles could act as a diffusion barrier to O and Ti therefore reducing the oxidation rate. The Al2O3 phase also forms an interlocking network penetrating throughout the oxide scale, reinforcing the fragile TiO2 containing scale. It is believed this composite system can provide a new generation of coatings to Ti based alloys, raising the application temperature of Ti alloys from ~650ºC to 800-900ºC without excessive scale spallation.

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