Effect of MgO:Li_2O molar ratio and sintering temperature on properties of vitrified bond and cBN grinding wheel

The vitrified bonds with different molar ratios about MgO∶Li2O(M) and cBN wheels were prepared at the base of ZnO-Na2O-SiO2-Al2O3-B2O3 ceramic system.X-diffraction analysis,SEM and thermal expansion coefficient tests were used to study the influence of M and sintering temperature on the properties of vitrified bonds and cBN wheels.The results show that with the M value increasing,the soften temperature,refractoriness and chemical stability of the bond increase,while the thermal expansion coefficient increases and then decreases.When the M value is 0.67,the increasing of the temperature restrains the quartz crystal separating.Meanwhile,the content of Mg(Zn)Al2O4 crystalline phase increases,and the size decreases at first and then increases.Moreover,when the temperature reaches 870 ℃,the grain size is the minimum about 2 μm,and the most compact microstructure is obtained.At the same time,the bending strength of the bond reaches the maximum value of 136.28 MPa.As the sintering temperature increasing,the porosity and water absorption of cBN wheel decrease at the beginning and then increase.However,its bulk density,hardness,bending strength,abrasion and grinding efficiency exhibit contrary trend.When the temperature is 890 ℃,the abrasion and grinding efficiency reache the maximum values of 98.72% and 1.3675 g·min-1 respectively.