Synthesis Mechanism of Reactive Plasma Sprayed Al-Fe2O3 Composites Under Atmosphere and Low-Pressure Ambient Conditions

Reactive plasma spray (RPS) technique is frequently used to prepare high-performance coating materials with different application requirements. Based on the classical thermite reaction, the Al-Fe2O3 coatings were fabricated by RPS under atmosphere and low-pressure ambient. The phase compositions and microstructures of the obtained coatings were characterized by XRD, SEM and EDS. Moreover, the reaction mechanisms of thermite reaction of Al and Fe2O3 in sintering and RPS process were elucidated. The DTA analysis results indicate that the main sintering products are Fe, Al2O3 and FeAl phases under prolongated reaction condition with Ar gas protetion. However, low oxygen partial pressure leads to the formation of FeAl2O4 hercynite phase as an intermediate product during spraying. In atmosphere-reactive plasma spraying (A-RPS), such phase can be retained in the final coating under extremely fast cooling rate. Furthermore, it can also be continuously reduced to FeAl phase in the low pressure Ar-H-2 ambience due to the deoxidation effect and long in-flight distance of plasma jet.