The microstructures and tribological properties of composite coatings formed via PTA surface alloying of copper on nodular cast iron

Abstract

Abstract To improve the tribological properties of automobile stamping dies, Cu-rich particulate composite coatings were synthesized via plasma transferred arc alloying (PTA) of copper on ferritic nodular cast iron substrates. The plasma transferred arc heat input has an important effect on the synthesis of composite coatings. At a low heat input of 202 J/mm, a double-layer structure with both a Cu-rich layer and an Fe-rich layer is observed. As the heat input increases, the volume of the Cu-rich layer significantly decreases because the Cu is further mixed into Fe-rich layer. When the heat input is increased to 260 J/mm, a single Cu-rich particulate composite coating is synthesized in the molten pool. Microstructural analysis reveals that Fe-rich particles are embedded in the Cu-rich matrix, while Cu-rich particles are embedded in the Fe-rich matrix, which consists predominantly of residual austenite, acicular martensite and an interdendritic eutectic carbides. The microhardness of the Cu-rich particulate composite coatings is measured, which is much higher than that of the untreated substrate material but lower than that of the remolten layer without the Cu additive. Sliding wear tests are carried out on the composite coatings at room temperature (RT) and 773 K. The results exhibit a much better wear resistance of the composite coating compared to the untreated material. The Cu-rich particles contained in the composite coatings play an important role in the antifriction properties, which can be attributed to the formation of protective Cu films on the friction surface.