Systematic measurements of heat fluxes into the substrate under the conditions of APS and HVOF have been performed with the use of a specially designed calorimeter. Results of measurements are presented in terms of the heat absorbed by a 150 mm diameter disk related to the electrical input power (EIP) and/or to the plasma/gas enthalpy. Depending on the process conditions heat flux into the substrate could reach as much as 20 per cent of the torch input power. Influences of gas composition, torch power and standoff distance on the heat transfer efficiency as well as the radial distributions of heat fluxes have been studied in detail and compared for three types of guns. Data obtained from the measurements of the radial distribution of heat fluxes in the plasma plume allowed estimating effective plasma jet diameter and the heat flux density, respectively. Rates of jet expansion differ significantly between the F4 and PlazJet plasma torches. Direct measurements of the substrate temperatures with the use of thermal paints have been performed and temperature patterns were compared with the results of 3D heat transfer modeling. Experimental values of heat fluxes were used in the calculations. Comparison showed that the experimental data on heat transfer efficiency could be used for accurate predictions of the substrate thermal conditions during thermal spraying.

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