The XRD patterns of the prepared samples are shown in Fig.1. TiC, TiN, Ti(C,N), Mo0.84Ni0.16, and Fe0.36Ni0.64 peaks were observed for the cermet coating. The solidification of the mixed liquid metal composed of Mo, Ni, and Fe resulted in the formation of Mo0.84Ni0.16 and Fe0.64Ni0.36 solid solution because of the melting of the metal materials according to the cladding characteristics. Because TiC and TiN exhibit the same crystal structure, that can form a continuous solid solution at a high temperature based on the Hume-Rothery rule, diffraction peaks of the Ti(C,N) solid solution were observed with increase of TiN content.Furthermore,a small amount of TiC and TiN, led to the peaks for the(200) and(220) crystal faces, which co-existed with Ti(C,N). In particular, three distinct(002) diffraction peaks corresponding to TiC, TiN and Ti(C,N) were obtained when the TiC/TiN ratio was 3:1. This was likely the result of insufficient diffusion of atoms, owing to the rapid melting and crystallisation under the laser.
Fig. 1. XRD patterns of the cermet coatings prepared by laser cladding.
SEM images of the samples are provided in Fig.2, and show that the cermet coatings exhibited compact structures. Melting, diffusion, and solidification of the ceramic and metal powders rapidly occurred during laser processing. However, the cermet-coating microstructure differedwith increasing TiN content. The scaly microstructure of sample 1 is shown in Fig.2(a), and the scaly structure becomes smaller in the inset of Fig.2(b). In Fig.2(c), the surface of sample 3 is rough, which may increase optical trap absorption. However, compared with sample 3,a flat surface was observed in Fig. 2 (d) and (e) when the TiN content was > 30 wt. %.
Fig.2. SEM images of the TiC/TiN-based cermet coatings.
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