3.2. Single particle impact tests under high temperature corrosive environments
Fig. 8 shows the observations of impact craters on the films formed on the mild steel in various high temperature corrosive environments. The upper photographs were taken just after the impact of 3 mm in diameter at 70 ms−1 when the film thickness was about 35 μm. The lower photographs were taken on about fifteen hours after the impact. It can be seen that the narrowly spalled areas (bright) appear at the crater rim in the upper photographs, and the wide circle areas are accompanied by radial cracks around the impact crater in the lower photographs. The size of the two areas changed not only with the corrosive environment but also with the conditions of particle diameter, impact velocity and film thickness.