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Typical microstructure of HVOF Cr3C2–NiCr coatings

Time:2022-03-22 10:26:17  From:  Author:

The typical microstructures of the HVOF sprayed Cr3C2–NiCr coatings deposited with four different spray conditions are shown in Fig. 1. It was clearly recognized that the coatings consisted of lamellae elongated in the direction parallel to coating surface. All coatings present a dense microstructure with a few pores visible. The measurement of density of the coating yielded the porosity less than 1% for all coatings. A close examination of the microstructure reveals that carbide particles were distributed in the coating evenly. Furthermore, it was found that the size, shape and content of carbide particles within the as-sprayed coatings changed with spray parameters.

Fig. 1. Microstructure of HVOF sprayed Cr3C2–NiCr coatings in different deposition conditions.

Within the coating deposited at comparatively lower flows of propane and oxygen as shown in Fig. 1b, large carbide particles in an angular shape similar to that in the starting powder were present with an inhomogeneous distribution. On the other hand, the coating deposited at higher flows of both propane and oxygen and a long spray distance contained less carbide particles (Fig. 1a). Moreover, carbide particles in such coating have a round shape. This implies that under a condition of high propane flow the heating of the spray particles was enhanced which led to a partial melting of carbide particles. As the deposition was carried out with moderate propane and oxygen flows, the resultant coating contained a large amount of fine carbide particles and carbide particles were distributed comparably homogeneously (Fig. 1d).


 

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