Interfacial microstructure and mechanical properties of CBN brazed in a continuous tunnel furnace with low-temperature Sn-Cu-Ti filler alloy

Abstract

Currently, the most common process for manufacturing brazed cubic boron nitride (CBN) tools is vacuum brazing using Cu-based active filler alloys. However, the high brazing temperature of Cu-based alloys and the long heating time in a vacuum furnace inevitably cause severe thermal damage, thereby compromising the mechanical properties of the brazed CBN abrasives. In this study, CBN abrasives were brazed using low-temperature Sn-Cu-Ti filler alloys in a continuous tunnel furnace. The final contact angles of the Sn-Cu-Ti filler alloys on the surfaces of the brazed CBN abrasives were determined at 650 °C. When the Ti content in the alloy was 4 %, the final contact angle was 37.2° and the CBN maintained a good exposure height and achieved a firm holding force. The interfacial microstructure was analysed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). It was found that a layer of needle-like compounds, primarily comprising TiB₂ and TiN, with an approximate thickness of 5 μm, was formed at the interface, indicating the formation of a chemical–metallurgical bond between the Sn-Cu-Ti alloy and CBN abrasive. The residual stresses and mechanical properties of brazed CBN abrasives with Sn-Cu-Ti and traditional Cu-based alloys were measured and compared. The results showed that compared to the brazed CBN with the Cu-based alloy, the average residual stress of the brazed CBN with the Sn-Cu-Ti alloy was reduced by 25.2 %, while the compressive strength and impact toughness increased by 25.3 % and 13.8 %, respectively. The experimental results provide new insights into reducing thermal damage to CBN for improving the processing performance of brazed CBN tools.