Interfacial microstructure and mechanical properties of synthetic diamond brazed by Ni-Cr-P filler alloy

Active brazing is a promising technique for the fabrication of high-performance diamond abrasive tools, which is especially beneficial to the manufacturing of hard-to-machine materials such as ceramics and high-strength metals. Ni-Cr based filler alloys are commonly used to fabricate diamond abrasive tools under different brazing strategies. However, in the previous studies brazing conditions are inconsistent, and the mechanisms of the interface reaction and the microstructure evolution in the synthetic diamond and Ni-Cr-P filler alloy reaction system are not well understood. In this work, the interface reaction and solidified microstructure in AISI 1045 steel and diamond grit joints brazed using a commercial Ni-Cr-P filler alloy were systematically studied at a typical brazing temperature of 950 °C. A rapid formation of both Cr3C2 and Cr7C3 compounds was observed at the very early stage of liquid-solid reaction. An anomalous delamination of Cr7C3 and formation of primary (Ni,Cr)5P2 dendrites and FeNi3 phase in near-eutectic Ni-P matrix were observed after extended brazing reaction. Moreover, the effect of brazing time on the residual thermal stresses, and hence the integrity of brazed synthetic diamond, were experimentally revealed and discussed with the implications for the fabrication of diamond abrasive tools. •Interface chromium carbides nucleate rapidly at the very early stage, but delaminate after long time brazing.•Delamination of chromium carbides and microstructure variation are due to continuous diffusion of Fe from steel substrate.•As brazing time increased, the integrity of brazed diamond grits deteriorates, but the compressive strength increases.