A Comparative Study on Boride Layer Morphology of Fe-4Co, Fe-4V and Fe-4W Binary Alloys

In this study, the pack boronizing behavior of Fe-4M alloys (at.% M=W, V, Co) along with pure iron was investigated. The boronizing process was carried out at 1100°C for 3 h. The morphology, microstructure, boride layer thickness and surface properties of the formed boride layers were characterized by XRD, SEM-EDS and profilometry. The average boride layer thicknesses were 85 μm, 130 μm, 275 μm and 280 μm for Fe-4W, Fe-4V, Fe-4Co binary alloys and pure Fe, respectively. The surface roughness was not changed with the addition of alloying element into the substrate. FeB and Fe₂B phases exist on all boronized samples, but their ratio changes owing to alloying elements in the substrate. The saw-tooth morphology has transformed to a smoother boride layer with the addition of alloying elements of W and V, though Co addition was ineffective on saw tooth morphology. In addition, a transition zone under the boride layer was observed for the boronized Fe-W and Fe-V alloys. The formation of precipitates of boride of alloying elements was evident in the boride layer and in the transition zone for borided Fe-4V and Fe-4W alloys. Co has made a solid solution with iron in boride by replacing iron in the boride lattice.