Splat Morphology and Microstructure of Plasma Sprayed Cast Iron With Different Preheat Substrate Temperatures

Abstract

A cast iron coating is a prime candidate for the surface modification of aluminum alloys for antiwear applications because cast iron is inexpensive and exhibits superior wear resistance arising from the self-lubricating properties of graphite. In the present study, fundamental aspects of a plasma sprayed cast iron coating on an aluminum alloy substrate, including (1) the effects of preheat substrate temperature on the splat morphology, (2) the formation of a reaction layer and pores, and (3) the splat microstructure, were investigated in low-pressure plasma spraying. With an increasing substrate temperature, the splat morphology changes from a splash type to a disk and star shape. Deformed substrate ridges mainly resulting from the slight surface melting, are recognized adjacent to the splat periphery at high substrate temperatures. The flattening ratio of disk splats decreases with substrate temperature because the ridges act as an obstacle for splat expansion. A reaction layer composed of iron, aluminum, and oxygen is ready to form at high substrate temperatures, which, along with the deformed ridges, improves the adhesive strength of splats. However, the pores appear at the splat interface at low substrate temperatures, which hinder the formation of a reaction layer. The amount of graphitized carbon increases in cast iron splats with an increase in substrate temperature.