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

Abstract

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 prolometry. 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 ineective 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.

Pack-boriding of low alloy steel: microstructure evolution and migration behaviour of alloying elements

“…The nucleating and growing boride particles discard alloying elements because the boride has low or no solubility as most of the alloying elements present in the steel (Figs. 4-6) [4][5][6][7][8][9][10][11][12][13]. Boride has the lower solubility (as compared to the non-boride region or core) for Cr, Mn, Mo and Ni, and almost zero solubility for C, Si, and Al.…”

“…Boronizing, a thermo-chemical treatment, is accompanied by the controlled diffusion of boron into the metal surface producing different phases of metal borides (M-B, M = Fe, Cr, Ti, Ni, V, Mo, Mn, W, etc.) [4][5][6][7][8][9][10][11][12][13][14]. A considerable improvement in the quality of the surface layer is possible through combining the boronizing treatment with other surface treatments (like borocaburising, laser treatment on the boronized surface, etc.)…”

“…The alloying chemistry has a significant influence on the boronizing behavior. The effect of various chemical elements on the boronizing response of pure iron was the subject of attraction in many kinds of literature [5][6][7][8][9][10][11][12]. The microstructure of the boronized layer, especially, the morphology of borides is dependent on the alloys, where the alloying elements can modify the solubility and diffusion of constituents [16,23].…”

“…However, high alloy steels have an almost flat interface between the boride layer and substrate [21,23]. Presence of W and V as alloying elements transforms the saw-tooth morphology into flat boride surface with smooth interfaces, along with the formation of transition zone that is rich in precipitates of W and V [10,11]. There, the alloying elements can lead to the formation of a mixed boride phase in the layer.…”

“…It was noted that the alloying elements could affect the kinetics, hardness, surface roughness, and tribological behavior of the boride layer [7,8]. The thickness of the boride layer decreases due to the addition of alloying elements [10,11]. Most of the archival literature has given a specific focus on the binary Fe-M alloys.…”