On bond wear, grit-alloy interfacial chemistry and joint strength of synthetic diamond brazed with Ni-Cr-B-Si-Fe and Ti activated Ag-Cu filler alloys

A multi-point brazed diamond tool requires high wear resistance of bonding alloy and strength of the brazed joint. In this work, two active brazing alloys, i.e., Ni-Cr-B-Si-Fe and Ag-Cu-Ti were used for brazing synthetic diamond grits on a medium carbon steel substrate under a high vacuum environment. The performance of the brazed joints was subsequently investigated and compared. The microstructure of the filler alloys was found to play a key role in influencing the bond wear characteristics, grit-alloy interfacial chemistry and strength of the brazed joint. Formation of Cu4Ti compounds in Ag-Cu-Ti alloy and boride and silicide compounds in case of Ni-Cr alloy contributed to the enhancement of hardness of the alloys. The bond wear characteristics of Ni-Cr alloy were substantially superior to that of Ag-Cu-Ti alloy. A single grit test of the brazed samples was carried out to investigate the failure pattern of the brazed joints. Ni-Cr brazed joints predominantly failed at the bond level. The residual stress and microstructural flaws in the form of microcracks at alloy-grit interface of the as-brazed test samples led to such a failure. In contrast, no such crack was detected in the case of Ag-Cu-Ti alloy and the joints failed by ductile fracture of alloy near to the interface, leading to diamond pull out. The present study elucidates the differences in wear, strength of bond and failure pattern of the brazed joints in the light of alloy and interfacial microstructure.