Interfacial reaction and wetting behavior of active Ag-Cu filler alloys on surface of cBN grits and its influence on failure patterns of brazed joint

Abstract

Cubic boron nitride (cBN) abrasive grits are often brazed on steel to produce monolayer grinding wheels. Establishing a strong cBN brazement is a challenge. In the current work, performance of three different active Ag-Cu alloys have been investigated in-depth considering microstructure of alloys, interfacial reaction phase formation and wetting capability of the reaction product towards the alloy. In the current study, all three alloys contain Ti as active element but with different wt%. One of alloys was so chosen that Indium (In) was present as an additional alloying element, which is responsible for its low liquidus temperature, high Young's modulus and good ductility. Segregation of Ti towards the interface was critically examined. To evaluate joint strength, a miniature twin-ring grinding wheel was produced with these alloys. Interestingly, the alloy containing higher Ti, which required higher brazing temp, resulted in intense reaction but with inferior joint strength. On the other hand, the very presence of indium in Ag-Cu alloy, containing low wt% of Ti not only lowered the brazing temperature but also led to effective wetting and higher joint strength. Failure pattern indicates the prevalence of high residual stress at the bond level for the alloy containing the highest percentage of titanium.