Experimental and theoretical investigations of heat flux in thermal spray processes for metallizing heat-sensitive substrates

• Incident heat flux measured by k-type sensors is comparable to Gardon gauge values. • High flow rate flame spray parameters increase substrate heat flux density by ∼ 37 %. • Feedstock material properties and scan speed influence substrate heat flux density. • Wire arc spray coating process shows ∼ 50 % lower heat flux than flame spray process. • Fine feedstock, short barrel, tuned parameters cut incident heat flux ∼ 34 % in HVOF. Heat flux interaction and thermal management during the thermal spray (TS) process are critical, especially for coating heat-sensitive substrates. The selection of an inappropriate coating method can lead to thermal degradation of the substrate and negatively affect adhesion strength and other properties. This study presents an integrated experimental and theoretical framework to estimate and compare heat flux impinging on a substrate during an individual spray pass for various thermal spray processes, to identify an optimal spray process to coat substrates prone to thermal damage. The theoretical framework was validated by comparing it with Gardon gauge experimental results. Aluminum, aluminum bronze, and stainless steel were selected as feedstock materials for the flame spray and wire arc spray coating process. Tungsten carbide nickel–chromium (WC-NiCr) feedstock materials with two particle size distributions were selected to spray using the high-velocity oxygen fuel spray coating process. The effects of feedstock properties and process parameters on heat flux impinging on the substrate in a spray pass were investigated. The results indicate that incident heat flux to the substrate for the wire arc spray coating process is ∼ 50 % lower than the flame spray coating process across all feedstock materials for similar coating thickness per pass. Thermal conductivity and melting point are important feedstock properties that impact the substrate heat flux density. Smaller WC-NiCr particle size and optimized parameters decrease substrate heat flux density during the high-velocity oxygen fuel spray coating process, reducing the impact when metallizing thermally-sensitive materials.