Figs. 1 and 2 show the SEM morphologies of the worn Fe–Al coating and Fe–Al/WC composite coating after sliding 500m with 3 and 7N loads. Furrow of micro-plowing can be observed clearly on wear track of both coatings, which suggests micro-plowing action of hard asperities of Si3N4 ball and wear debris during sliding wear test. The wear tracks of both coatings tested with 7N (Figs. 1b and 2b) are wider than that with 3N (Figs 1a and 2a). The worn surfaces can be divided into two kinds of regions with difference in color: rough gray regions and discontinuous smooth dark regions. EDS analysis indicated the gray regions to be fresh coating, and the discontinuous dark regions to be oxide films formed by friction heating during sliding.
Fig. 1. SEM morphologies of the worn Fe–Al coating: (a) wear track with a 3N load; (b) wear track with a 7N load; (c) higher magnification of rectangular area in (b) showing oxide film formation during sliding wear; (d) cross-section micrograph showing cracks between splats. (The arrows indicate the width of the wear track.)
Fig. 2. SEM morphologies of the worn Fe–Al/WC composite coating: (a) wear track with a 3N load; (b) wear track with a 7N load; (c) higher magnification of rectangular area in (b) showing oxide films and WC/W2C particles on the worn surface; (d) cross-section micrograph showing cracks between splats. (The arrows indicate the width of the wear track.)
Table 1 shows the main chemical composition of as-sprayed coating and the worn coatings surfaces by EDS at different loads. After sliding, the contents of O on the worn surfaces tested with 7N are higher than that with 3N, which indicates that higher friction contact temperature is reached on the worn surfaces at high normal load. For Fe–Al/WC composite coating, WC/W2C particles can be seen protruding from the worn surface (Fig. 2c), which will resist micro-plowing from the Si3N4 ball. There also exists a little Si on the worn coatings surfaces, which indicated that the Si3N4 ball will produce debris during sliding which will cause abrasive wear. But this abrasive wear is slight because the contents of Si3N4 debris are very limited. From the SEM micrographs of worn surfaces, the wear damage mechanism of the coatings cannot be observed clearly due to oxide films on the worn surfaces. Figs. 1d and 6d are cross-section SEM micrographs of the worn coatings. It can be seen that, the cracks initiate and propagate through the weakest boundaries between splats of the coatings, resulting in fracture and spallation of splat from coatings and generating the wear debris. Therefore, the predominant wear mechanism of both Fe–Al and Fe–Al/WC composite coatings appears to be delamination.
Table 1
Main chemical composition of the worn surfaces by EDS at different loads
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