Effect of the substrate temperature on properties of plasma sprayed Al2O3 coatings

Al2O3 coatings were deposited on AISI 304L stainless steel substrate at 25, 300 and 500 °C substrate temperatures by the plasma spray process. The results show that the hardness of Al2O3 coating increased and the porosity decreased with higher substrate temperatures. X-Ray diffraction was used to characterise the phase compositions. The amount of α-Al2O3 gradually disappeared and γ-Al2O3 and oxidation of bond coat increased with higher substrate temperature. For Al2O3 coating deposited various substrate temperatures, the thermal expansion coefficients were measured in the temperature ranges from 25 to 1000 °C. The increase of the substrate temperature was resulted in increasing of the thermal expansion coefficient of Al2O3 coatings without bond coat. However, higher substrate temperatures were increased the amount of the oxide phases in bond coat and decreased the thermal expansion of Al2O3 coatings with bond coat.