The influence of substrate temperature on properties of APS and VPS W coatings

• Atmospheric plasma spray and vacuum plasma spray of tungsten were studied.
• The effect of substrate temperature Ts was separated from other parameters.
• The influence of Ts depended on particle in-flight state.
• Strongest effect of Ts was observed for optimum particle in-flight state.

The effect of substrate temperature on integral properties of W coatings was investigated. Cooled sample holder enabling simultaneous deposition on substrates with different temperatures was used. The spraying was performed by atmospheric plasma spray (water stabilized torch) and vacuum plasma spray (RF inductively coupled torch). Three torch power levels were used for vacuum plasma spray to obtain different spray particle in-flight properties. It was observed that the substrate temperature influenced the porosity, coating modulus, hardness and thermal conductivity of the deposits. The strongest influence of the substrate temperature was observed for the optimal spray condition resulting in the lowest porosity deposit. For the other deposits, the presence of W oxides, condensed W phase, unmelted feedstock particles and splashed splats decreased the values of all abovementioned coating properties.