Study of solidification behavior and splat morphology of vacuum plasma sprayed Ti alloy by computational modeling and experimental results

The microstructure of Ti–6Al–4V alloy manufactured by vacuum plasma spraying consists of individual lamellae, inter-lamellae boundaries, and porosity. Mechanical properties of the as-sprayed structure depend mainly upon the solidification behavior and resultant microstructure and morphology of the individual splats and cohesion between splats. Using a three-dimensional numerical model, the cooling rate and solidification behavior of a single Ti–6Al–4V droplet (50 μm) impacting on a titanium substrate under vacuum plasma spray conditions were investigated. Results were verified with experimental observations in single splats and as-sprayed microstructures obtained by vacuum plasma sprayed form of Ti–6Al–4V alloy. The average cooling rate of a single splat obtained from the numerical simulation was on the order of 108 °C/s and the solidification front velocity was approximately 63 cm/s which is in the range of the rapid solidification. The thickness of the splat was calculated to be around 3 μm and the deposition efficiency was approximately 70%. These results illustrated good agreements with those obtained from experiments.