Effect of brazing time on microstructure and mechanical properties of cubic boron nitride/steel joints

The purpose of the present study was to investigate the effect of brazing time on microstructure and mechanical properties of cubic boron nitride (cBN)/steel (CK45) joints brazed with Cusil-ABA as an active brazing alloy. The brazing process was carried out using a tube furnace under high purity argon atmosphere and at a constant brazing temperature of 920 °C. The brazing time varied between 5 and 15 min. Microstructural examinations and phase analysis were performed using scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), and X-ray diffraction (XRD) techniques. Using a shear strength testing method, the mechanical properties of the joints were measured. The results of the microstructural analyses indicate that joining is due to the formation of a reaction layer between cBN and filler alloy in addition to a diffusion layer between steel and filler alloy. By increasing the brazing time, these layers become thicker and more continuous, resulting in higher joint strength. The maximum shear strength was obtained for the samples brazed for 15 min and was about 129 MPa.