Effects of nano-AlN and sintering atmosphere on microstructure and properties of vitrified bond

The Na2O-B2O3-SiO2 glass with low thermal expansion coefficient and melting point is suited to manufacture vitrified bond superhard grinding tool. However, its bending strength, fracture mode, and chemical durability are lower. Some additives, such as alumina, calcium and/or zinc oxides, and so on, were added in the vitrified bond in order to improve the property of grinding tool. In this work, a new additive of nano-AlN was added in Na2O-B2O3-SiO2 vitrified bond for improving microstructure and properties of the vitrified bond. The Na2O-B2O3-SiO2 vitrified bonds with and without nano-AlN were sintered at different atmosphere. The effects of nano-AlN and sintering atmosphere on the microstructure and properties of Na2O-B2O3-SiO2 vitrified bonds were investigated. The results show that the highest bending strength, impact strength, and wear resistance were obtained when the Na2O-B2O3-SiO2 with nano-AlN of 6% was sintered at argon, because nano-AlN as crystallization nucleus promotes the crystallization of α-SiO2, β-SiO2, and tridymite during sintering process. The microstructures of the crystalline phases were refined. When the vitrified bonds with nano-AlN were sintered at air, the nano-AlN powder was oxidated and decomposed into Al2O3 and gas. The decomposition of nano-AlN increases slightly the bending strength and wear resistance of the vitrified bond due to the increasing amount of crystalline phase, but the decomposition of nano-AlN increases the amount of small close pores and size of crystalline phase, which results in the decreasing of impact strength of vitrified bond.