Interfacial microstructures and mechanical integrity of synthetic diamond brazed by a low-temperature Cu-Sn-Cr filler alloy

Abstract

To ensure the formation of metallurgical bonding of diamond abrasive grits, active brazing using the Cr-containing Ni-based filler alloys has been employed for decades. However, the high brazing temperature of Ni-based filler alloy inevitably induces intense thermal damage and impairs the mechanical properties of brazed diamond grits. In this study, a Cr-containing Ni-free CuSn filler alloy of melting point lower than that of Ni-based alloy was developed based on our previous wettability study. Interfacial microstructures and mechanical properties of diamond grits brazed using this newly developed Cu-Sn-Cr alloy and the commercial Ni-Cr-P alloy were investigated and comparatively analyzed. By using FIB-TEM, Raman spectroscopy and XRD techniques, a thin and uniform interfacial Cr7C3 chromium carbide was observed at interface between synthetic diamond grits and the Cu-Sn-Cr alloy brazed at 750 and 950 °C. The impact toughness (TI) of diamond grits brazed using Cu-Sn-Cr alloy was significantly improved as compared with the diamond grits brazed by commercial Ni-Cr-P filler alloy at 950 °C. It was found that the alloy composition played a more significant role in the interfacial carbide formation than brazing temperature. In particular, the decrease of C solubility in Cu-Sn-Cr alloy was the main reason for the refinement of interfacial chromium carbide and the improvement of mechanical properties. Experimental results obtained in this work lay a foundation for the further development of Cr-containing filler alloys for diamond brazing application.