Effects of brazing temperature on microstructure and properties of interface between cBN and Co-based active filler metals

Cubic boron nitride (cBN) was brazed by Co-based active filler metal. The effects of brazing temperature on the interfacial microstructure and properties of cBN specimen were investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and friction and wear testing. The results showed that when the brazing temperature was between 1473 and 1523 K, the Co-based active filler metal had good wettability to the cBN, and the filler metal/cBN interface was smooth, with a compact bonding, thus producing a continuous reaction layer with uniform thickness. XRD results indicated that Ti and Cr in the Co-based filler metal could interact with the B and N of the cBN at high temperatures, producing the TiN, TiB2, TiB, CrN and CrB compounds. The wear loss of the brazed specimen was decreased with the increase of brazing temperature. However, too high brazing temperature would lead to the increase of the volume of brittle compounds at the interface of the filler metal/cBN and thus trigger the initiation of micro-cracks in the cBN grains, which resulted in a slight increase of wear loss.