Effect of Na₂O Content on Properties of Na₂O-SiO₂-Al₂O₃-B₂O₃ System Vitrified Bond for Diamond Grinding Wheel

Na₂O-SiO₂-Al₂O₃-B₂O₃ system vitrified bonds with Na₂O mass fractions of 12.31%, 9.31% and 7.31%, respectively, were prepared by ball milling, and then the effects of Na₂O content on the phase composition, mechanical properties, coefficient of thermal expansion of the vitrified bonds before and after sintering, and on the bending strength of the vitrified bond combined diamond grinding wheel were investigated. The results show that relatively high content of Na₂O helped inhibit the precipitation of quartz phases. With the increase of Na₂O content, the hardness and bending strength of the vitrified bond decreased, and the coefficient of thermal expansion increased at relatively low temperatures (620-640℃) while first increased and then decreased at relatively high temperatures (660-680℃). When the mass fraction of Na₂O was 9.31% and the sintering temperature was 680℃, the obtained vitrified bond combined diamond grinding wheel had the highest bending strength of 53.3 MPa. The diamond grinding wheel prepared with the three vitrified bonds had a similiar microstructure.