ABSTRACT
In order to develop new-generation brazed cubic boron nitride (CBN) grinding wheels, the joining experiments of CBN abrasive grains and medium carbon steel using a powder mixture of Ag-Cu alloy and pure Ti as active brazing alloy were carried out at elevated temperatures under high vacuum conditions. The relevant characteristics of the special powder mixture and the microstructure of the interfacial region, which are both key factors for determining the joining behaviour among the CBN grains, the filler layer, and the steel substrate, were extensively investigated by means of differential thermal analysis (DTA), scanning electron microscope (SEM), and energy dispersion spectrometer (EDS), and X-ray diffraction (XRD) analysis. The results show that, similar to the Ag-Cu-Ti filler alloy, the Ag-Cu/Ti powder mixture exhibits good soakage capability for CBN grains during brazing. Moreover, Ti in the powder mixture concentrates preferentially on the surface of the grains to form a layer of needlelike T-N and T-B compounds by chemical metallurgic interaction between Ti, N, and B at high temperature. Additionally, based on the experimental results, the brazing and joining mechanisms were deeply discussed in view of the thermodynamic criteria and phase diagram of the Ti-B-N ternary system.
