Microstructure and Micro-Hardness of Al2O3-TiO2 Coating by Plasma Spraying on SKD61 Steel

In this research, the modified surface is created by cladding Al2O3 particles with 40% TiO2 particles on an SKD61 steel surface by plasma spraying method. The results indicated that the macrograph of the coating has no cracks, and the coating has an undulating flatness with relatively dark color and distribute uniformly. The coating surface can be divided into three distinct regions: the coating zone, the heat-affected zone, and the SKD61 steel substrate. The coating zone presents a smooth surface and does not have any porous inside it, indicating a good coating film. The microstructure of Al2O3-40%TiO2 coating mainly consists of plasma-spray stacked layers, includes two regions, in which Al2TiO5 phase appeared as gray regions while gamma-Al2O3 and alpha-Al2O3 particles appeared as white regions. The micro-hardness distribution of the coating showed that the average hardness of the Al2O3-40% TiO2 coating reaches the highest number with 816.3HV(0.1), while the heat-affected zone gains a hardness number of 595HV(0.1). Both of these zones' hardnesses are greatly higher than the hardness of the SKD61 steel substrate with 252.5HV(0.1).