Microstructure, residual stresses and shear strength of diamond-steel-joints brazed with a Cu-Sn-based active filler alloy

Brazing of diamonds is important in grinding technology. The brazing parameters can strongly influence the grinding tool's performance. In this work a Cu-Sn-based active filler alloy (73.9 Cu-14.4 Sn-10.2 Ti-1.5 Zr, wt.%) was applied to join monocrystalline block-shaped diamonds onto a stainless steel substrate using three different brazing temperatures (880, 930 and 980 °C) and two different dwell times (10 and 30 min), respectively. The characteristics of the joints were investigated by means of scanning electron microscopy and energy dispersive X-ray spectroscopy (microstructure and phase composition), by Raman-spectroscopy (residual stress) as well as by shear testing (bond strength). The microstructural investigations revealed an intermetallic interlayer of type Fe₂Ti at the steel-filler alloy interface, which grew with increasing brazing temperatures and longer dwell durations. The brazing parameters strongly affected the residual stresses in the diamond. Compressive residual stresses with a maximum value of − 350 MPa were found in the samples brazed at 880 and 930 °C, whereas tensile stresses of maximum + 150 MPa were determined in samples joined at 980 °C. The effect of the brazing parameters on the shear strength is very pronounced. The shear strength decreased from (321 ± 107) MPa at 880 °C, 10 min to (78 ± 30) MPa at 980 °C, 30 min.