Fig.1 gives the free surface(Secondary Electron) and polished cross section(Backscattered Electron) morphology of the NiCr/hBN-NiCr/CraC2 composite powders. It can be seen from Fig.1(a) that NiCr/hBN is spherical while the NiCr/CraC2 is irregular polygonal, which are consistent with the shape of the spray dried hBN agglomerate and starting CraC2. Most of the blended powders are in the size range of 45 to 120 um and the cores are cladded by a fine NiCr alloy layer. The cross section of the powders(Fig.1(b)) reveals some district areas due to the atomic contrast. The bright region corresponds to the NiCr binder phase, the angular gray region is CraC2 and the dark spherical region is related to hBN agglomerate. The cores have been uniformly and completely cladded by the NiCr alloy with a thickness estimated to be 2-3 um. The composite powder has a high apparent density of 2.05 g/cm3 and a good flowability of 40 s/50 g, which ensures that it can be freely delivered in the feeding pipes and injected into the center of the plasma jet.
Fig. 1. (a) Surface and (b) cross section SEM morphology of the NiCr/Cr3C2–NiCr/hBN composite powder.
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