Abstract
Microstructural characterization of a vanadium carbide (V2C and V8C7) surface compound layer was performed by electron backscatter diffraction (EBSD), scanning electron microscopy and transmission electron microscopy. The phase composition and phase distribution of the compound layer and the morphologies, grain sizes and crystallographic orientations of the vanadium carbides were investigated through elemental distribution and crystallographic analyses. The results indicated that the compound layer was composed of four distinct zones consisting of a compact and uniform V2C layer (thickness of 3.2 μm) over the topmost surface followed by a nonuniform V + V2C (2.4 μm) zone, a V8C7 layer (10.7 μm) and a relatively deep V2C + V8C7+α-Fe + Fe3C zone (23.2 μm). The V2C layer was found in the V-rich region, and the EBSD results revealed that this phase grew mainly along the {0001} and {11–20} orientations. However, the V8C7 phase appeared to be nearly random, which indicates that the growth of this phase had no specific orientation. The V2C and V8C7 phases exhibited low-angle grain boundaries, and their misorientation angle distributions were mainly concentrated within the range of 0–5°. Furthermore, nanoindentation tests demonstrated that the hardnesses of the V2C and V8C7 layers were 22.16 ± 0.52 and 32.42 ± 0.61 GPa, respectively. Examination of the vanadium carbide powders obtained by chemical extraction indicated that the V2C grains with a hexagonal structure exhibited equiaxial and short rod-like morphologies, and the V8C7 particles with a cubic structure possessed short rod-like and spherical morphologies.
Published Version
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