Discussion on the mechanism of creating a transferred layer of SiC shot particles on aluminum alloy by FPP treatment

In order to clarify the mechanism of creating a transferred layer of shot particles on the substrate surface by Fine Particle Peening (FPP), the surface of aluminum alloy was modified with SiC shot particles at room temperature, 100°C, 200°C and 300°C. The treated surfaces were characterized using a field emission-scanning electron microscope (FESEM), an energy dispersive X-ray spectrometer (EDX) and an X-ray photoelectron spectroscope (XPS). An SiC-rich layer in which small chips of shot particles were embedded was formed on the substrate surface by FPP treatment. EDX and XPS analyses revealed that the transferred fragments were only embedded into treated material without any chemical binding. The SiC-rich layer became thicker with an increase in heating temperature and was uniformized on the specimen treated at 300°C. The mechanism of the adhesion of a part of the shot particles induced by FPP treatment was analyzed. Analyses using EDX revealed the presence of particle fragments transferred to the collision dents. With an increase in the amount of collision, transferred fragments were embedded into treated material by deformed material due to a micro ploughing effect. In addition, analyses using a high-speed camera revealed that collision of shot particles occurred during FPP treatment.