Fig. 8 Wear weight of coatings
3. 2 Experimental results of erosion
The wear weight was measured for the coatings with the different spraying distance. Of 5 specimens the results of two specimens are given in Fig. 7 (a) and Fig. 8 (a) for the loss weight, and Fig. 7 (b) and Fig. 8 (b) for the relative loss weight to the total weight. These results shows that the weight loss increases with blasting time and the specimens with the long spraying distance losses rapidly as compared with the ones coated by the short spraying distance. Particularly, wear becomes more conspicuous for the coatings with the spraying distance beyond 150min.
In order to discuss the obtained results with theory, eq. (2) is modified as follows,
V / KIC-3/4｡踪-1/4 (3)
Using the data given by Figs. 4, 6, 7 and 8 the relation between V / KIC-3/4 and H-1/4 is plotted in Fig. 9, where a solid line stands for theory given by eq. (3). It was confirmed that both the results get a good agreement.
Fig. 9 Relation among wear weight, fracture toughness and hardness
4. Surface topography
The surface topography of the eroded surface is very important because the material fracture initiates in its surface layer. In this chapter, two kinds of properties, surface roughness and fractal dimension are evaluated for the eroded surfaces.
4.1 Surface roughness
The surface roughness was measured by a stylus for the eroded surfaces which change with the blasting time. The measured result is shown in Fig. 10. The surface roughness rapidly decreases in the initial state with the blasting time. Although the initial roughness of the coatings sprayed by the longer spraying distance has much rougher that the one by the shorter spraying distance, their surface roughness asymptotically approaches to the same, constant value about 2 μ m.
