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.