Analysis of thermo-physical properties of NiCr HVOF coatings on T24, T92, VM12 and AISI 304 steels

Abstract This investigation reports on the thermal diffusivity of NiCr HVOF coatings on three ferritic steels (T24, T92 and VM12) and one austenitic steel (AISI 304) determined by laser-flash technique from room temperature up to 800 °C. The NiCr HVOF coatings were compact, dense, and well-adhered to the substrates with an average thickness of 194 ± 51 μm. The thermal diffusivity of AISI 304 austenitic steel increases steadily with temperature. In contrast, the thermal diffusivity decreases from room temperature till the Curie’s temperature and then increases up to 800 °C in the T24, T92 and VM12 ferritic steels. It is also shown that the substrate has a greater influence on the thermal diffusivity at lower temperatures while the coating increases thermal diffusivity of the overall sample (substrate + coating) at temperatures above 400 °C. Therefore, the intrinsic thermal diffusivity of NiCr, coating calculated with a 2-layer model, evolves similarly than the 304 steel with temperature.