Effect of Si coating on prevention of diamond degradation in diamond/glass composite

Oxidization of diamond in the sintering process of diamond/glass composites results in low compressive fracture strength (CFS) of the grit and uncontrolled expansion with many irregular pores in the composites, which causes low bending strength of the composites. In this paper, a Si barrier layer on the diamond surface was introduced for the first time in diamond/glass composites in order to resolve the above issues. The effects of Si coating on the properties of diamond grit and diamond/glass composites were studied. The results showed that the Si film prepared at 600 °C for 10 cycles has high thermal stability and excellent oxidization resistance, and could effectively protect grit from being oxidized. Uncoated diamond grit in the composites began to be oxidized at 812 °C, while oxidation of Si-coated grits could not be found below 1000 °C. Compared with uncoated grit, Si-coated grit had higher CFS after sintering at 850 °C. In the composites sintered at 850 °C, replacing uncoated grit with Si-coated grit, resulted in a decrease of volume expansion from 217.2% to − 28.6%, and an increase in bending strength from 9.5 MPa to 51.9 MPa.