The wear tests results include the friction coefficient and wear volume loss is shown in Figure 1. When the wear processes reaches a steady state, the average coefficient of friction of the substrate is 0.29, which is 2.6 times that of the cladding layer (0.11, Figure 1a). The wear volume loss of the substrate is 1.65 mm3, in comparison to 0.39 mm3 of the cladding layer (Figure 1b). Obviously, the cladding layer has a much better wear resistance than the substrate.
As presented by Figure 2a, the surface morphology of the worn substrate is featured by deep ploughed grooves with peeling of large oxide patches. There is obvious peeling and cracking on the surface, indicating that severe plastic deformation and destruction occurred on the surface during wear test. The EDS spectrum of the worn substrate (Figure 2c) shows that the surface layer mainly consists of Fe, Cr, Si, and O. The high oxygen content indicates that oxidative wear had occurred during the wear process. Simultaneously, the Si element had been transferred from the silicon nitride ball to the surface of the substrate, which indicates that the adhesive wear had occurred. Therefore, the main wear mechanism of the substrate is adhesive wear and oxidation wear. In contrast, as shown in Figure 2b, the surface morphology of the worn cladding layer is smooth, with only a small amount of slight ploughed grooves and little oxide particles. EDS test results (Figure 2c) show that the main elements of the surface particles are O, Mo, Cr, and Fe. The exfoliated oxide particles would act as abrasive particles and create ploughed grooves. Thus, the wear mechanism of the cladding layer is mainly abrasive wear with slight oxidation wear.
Figure 1. Test results of the wear behavior, (a) coefficient of friction of the substrate and the cladding layer, (b) wear volume loss of the substrate and the cladding layer.
Figure 2. The worn surfaces of the (a) substrate and (b) the cladding layer, EDS results of (c) zone 1 and (d) zone2.
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