Structural characterization of layers fabricated by non-vacuum electron beam cladding of Ni-Cr-Si-B self-fluxing alloy with additions of niobium and boron

Abstract

This paper is devoted to characterization of microstructure and phase constituion of coatings produced by non-vacuum electron beam cladding of Ni-Cr-Si-B self-fluxing alloy with Nb and amorphous B additions on mild steel substrates. The main purpose of this study was to form niobium diborides (NbB 2 ) belonging to AlB 2 structural family directly during the cladding process. For this reason we carried out a series of experiments with different ratios of (Nb+B (Am) ) and Ni-Cr-Si-B powders. When the starting material contained 15-40 wt.% of (Nb+B (Am) ) powder the NbC and (Cr, Fe) 23 C 6 carbides, as well as NbB 2 particles distributed in γ-(Ni-Fe) solid solution, were formed. When the starting powders contained 30-40 wt.% of (Nb+B (Am) ), NbB 2 formed shells around the NbC particles. The mechamism of shells formation, the ordering of γ-(Ni-Fe)-matrix and other structural peculiarities of the samples are discussed in the paper. Microhardness of the samples materials ranged from 450 to 950 HV 0.1 . • Ni-Cr-Si-B protective layers reinforced with NbB2 were fabricated on steel. • High-power electron beam accelerator was used to completely melt the alloy. • «NbB2 shell – NbC core» complex particles form at high concentrations of Nb and B. • Complex precipitates provide 2-fold improvement of Ni-Cr-Si-B-alloy microhardness. • The CuAuI type ordering of γ-(Ni-Fe)-matrix occurs in the cladding layer