Fig. 2 Erosion (blasting) process

Table 2 Blasting conditions

Fig. 3 Constituents of grit

　

3. Erosion

　

3.1 Theory

It is assumed that a lateral crack occurs on the target sample surface due to the collision of a single particle, and that the material peels off. According to Evans et al. [2], this wear weight V is given as follows,

V∞v^19/6R^11/3ρ^19/2H^-l/4K_IC^{-3 / 4} (1)

where R, v and ρ are the radius of a collision particle, its speed and density, respectively. H and Kic are the hardness and fracture toughness values of the target. Since the same grit and its speed are used in this experiment, eq. (1) can be rewritten as follows,

V｡踪 ^-l/4K_IC^{-3 / 4} (2)

In order to calculate eq. (2), we need the hardness and fracture toughness of the specimens.

Using a micro-Vickers hardness tester, hardness was measured for the coated specimens and the results are given in Fig. 4 with respect to the spraying distance. It can be seen that hardness decreases with the spraying distance. The results suggests that the bonding strength between lamellae becomes weak with the increase of the spraying distance. The fracture toughness KIC was measured by indentation method. The indent on the specimen surface was shown in Fig. 5. Using the crack length extended from the diamond corners, the fracture toughness is evaluated by the following formula,

where E is the Young's modulus, P is the indention load, and C is the median crack radius. The evaluated fracture toughness was shown in Fig. 6 with respect the spraying distance.

　

Fig. 4 Vickers hardness

Fig. 5 Indent on specimen surface

Fig. 6 Fracture toughness

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