Contact interaction of chromium diboride with nickel-based self-fluxing alloy

Abstract

The contact interaction between the Ni-based self-fluxing eutectic alloy and hot-pressed chromium diboride ceramics was studied by the sessile drop technique in vacuum at 1100 °C. The structure and phase composition of the initial NiCrBSiC alloy were examined. The chemical interaction between components in the NiCrBSiC system was found to occur in the melting process. The structure of the initial NiCrBSiC alloy consisted of chromium borides and carbides distributed in the metal matrix. Actually, the composite material (but not the alloy) took part in the wetting of chromium diboride. The wetting kinetics in the NiCrBSiC-CrB₂ system was studied. The NiCrBSiC self-fluxing alloy was shown to wet CrB₂ to form contact angle θ = 17º. Intensive chemical interaction between the alloy and substrate chemical elements was observed in the NiCrBSiC–CrB₂ system. The distribution of chemical elements in the interaction area of the NiCrBSiC–CrB₂ system was analyzed. Chromium was an interfacial active element in this system and the contact interaction proceeded through dissolution of the CrB₂ ceramics along the grain boundaries simultaneously with penetration of the Ni-based alloy. The contact interaction resulted in CrB and Cr₂B, having lower microhardness than CrB₂. Interaction in the NiCrBSiC–CrB₂ system thus changes the composition of ceramics resulting in decrease in the microhardness of the composite material. Hence, the use of CrB₂ particles as reinforcing additives for the NiCrBSiC self-fluxing alloy to produce composite powders for thermal sprayed coatings with high wear resistance is not reasonable.