Microstructural evolution of low-pressure plasma-sprayed Ti–6Al–4V coatings after heat treatment

Abstract

In this study, we deposited Ti–6Al–4V coatings by low-pressure plasma spraying using hydride-dehydride (HDH) powders with particle sizes of 10–60 and 10–150 μm, followed by annealing at 750–1100 °C. The coating microstructure changes from the lamellar structure of the as-sprayed coating to the equiaxed grain structure and the coating hardness increased after annealing. The increase in the coating hardness depended on the microstructure of the as-sprayed coating. The lattice constant c/a ratios and oxygen contents of the coatings were calculated from their diffraction peaks. Coatings deposited by low-pressure plasma spraying contain oxides, which can dissolve in titanium to form an interstitial solid solution after annealing. The dissolution of oxygen in Ti–6Al–4V coatings increases with the annealing temperature. The annealed coatings deposited using larger HDH particles (10–150 μm) exhibited higher toughness than those deposited using smaller particles (10–60 μm).