Figure1 shows the SEM image of laser cladding NiCrBSi, TiN and h-BN metal-ceramic composite coating. The thickness of the self-lubricating coating is about 1.5 mm according to the proportion of the photograph in figure1(a). There is an obvious white bright line between the coating and the substrate. The enlarged picture is shown infigure1(b). The white bright line is the fusion line between the cladding layer and the substrate. The coating is well metallurgical bonding with the substrate and microstructure is uniform and fine.
Figure 1.Cross-section morphology of laser cladding Ni-based alloy, TiN and BN composite coating:(a)Macroscopic cross-section SEM image and(b)SEM image of coating and matrix bonding zone.
Figure2 is an XRD diffraction pattern of composite coatings of alloy powders with different mass fractions. As the cooling process of laser cladding is a non-equilibrium solidification process. Moreover, the diffraction peaks of the phase overlap with each other and coexist in multiple phases. Therefore, it is necessary to combine with the EDS energy analysis phase transformation process. It can be seen from the figure2 that the peak position and peak value of the phase of the self-lubricating cladding layer change with the change of the mass fraction of BN. The composite cladding layer is mainly composed of NiTi2, TiN0.3, BN,γ-Ni, TiB and TiN phases. The peak of TiN and NiTi2 diffraction at 41.4° is the highest when TiN powder is added only. With the addition of BN powder, the diffraction peak of γ-Ni and TiN0.3 phase rises and the diffraction peak of NiTi2 decreases. The diffraction peaks of BN and TiB were observed at the 41.4°and 42.8° diffraction peaks position respectively, and a new TiN peak was found at the 72.5° position. Under the action of laser, part of BN is decomposed into B and N atoms evenly distributed in the coating. New TiN, TiN0.3 and TiB are preferentially formed owing to extremely high affinity of Ti with both B and N, resulting in the increase of γ-Ni. The uniform distribution of TiN, TiN0.3 and TiB reinforcing phases can significantly improve the hardness and wear resistance of the coating.
Figure 2.XRD analysis of laser cladding wear resistant coatings.
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