Papers by Author: Y.M. Zhu

Abstract: Alkaline-earth metal oxides (MgO, CaO, SrO and BaO) were introduced to Na2O-B2O3-Al2O3- SiO2 vitrified bond, and their effects on the properties of the vitrified bond were investigated through the measurements of refractoriness, fluidity and bending strength. The results showed the refractoriness of the vitrified bond was reduced and the fluidity of the bond increased with the addition of alkaline earth metal oxides in the order of CaO>SrO>BaO>MgO. When 2-10wt% MgO, CaO and BaO was added into the bond respectively, the vitrified bond was relatively dense due to high viscosity, and the strength was all improved to some extent. However, when more than 4wt% SrO was added, the strength decreased sharply because of the deterioration of microstructure. It was concluded that the bending strength of the bond was affected by alkaline-earth metal oxides in the order of CaO>MgO>BaO>SrO.

Abstract: The crystallization and sintering of the Li2O-Al2O3-SiO2 glass powder compacts were studied. Results showed the relative densities of the sintered compacts with lower crystallization temperatures were higher than those with higher crystallization temperatures. A small amount of residual glass in the crystallized compact was good for sintering and densification. Compared with the heat treatment time, the heat treatment temperature was an important factor for the crystallization and sintering of glass powder compacts. The crystallized compacts with a small amount of residual glass should be sintered at a relatively higher heating rate under the prerequisite of keeping sintered compacts from deformation.

Abstract: Advanced ceramics has many advantages and great potential of application, but its high machining cost resulted from its high hardness and brittleness limited its application. Grinding with superabrasives is the most suitable and effective way for machining of advanced ceramics. Grinding with vitrified bond CBN wheels is a developing direction of high efficient grinding for engineering ceramics. Grinding of the promising composite ceramics of TZP/Al2O3 with vitrified bond CBN grinding wheels was investigated in this paper. The results showed that higher material removal rates and satisfactory surface finish were achieved, CBN wheels with coarser grit size or with higher CBN concentration had higher grinding ratio. G-ratio increased with the increasing of wheel speed.

Abstract: In this paper, the performances of CBN abrasives with and without Ti coatings and their changes during heat treatment were investigated under the same conditions. The results showed that the single particle compressive strength and the impact toughness for CBN abrasives with Ti coatings were lower than these of CBN abrasives without Ti coating. Ti coating on the surface of CBN abrasive particles oxidized and formed TiO2 with discontinuous structure at above 650°C during the firing process. The poor oxidation resistance of Ti coating and the discontinuous structure of its oxidation product could not protect CBN abrasives from heat damage, therefore could not improve properties of CBN abrasives.

Abstract: Cubic boron nitride(CBN) is a superhard materials with many advantages and many uses. Vitrified bond CBN grinding tool is a promising abrasive tool of high performance used for high speed, high efficiency, high precision grinding with lower grinding cost and less environment pollution. Sintering of vitrified bond CBN grinding tool was investigated in this paper. The results showed that practical sintering temperature of this tool was much lower than the initial oxidation temperature of CBN particle measured by comprehensive thermal analysis. The upper limit of sintering temperature should be determined by taking account of the thermal analyzing results, heating process of CBN and its change in strength and structure. Within the sintering temperature range of the vitrified bond, relatively higher sintering temperature was beneficial to the strength of bond bridge and the holding strength between bond and CBN abrasive particles. CBN tool sintered at relatively lower temperature tended to fracture through the bond bridge, while the one sintered at higher temperature tended to fracture along the boundary between CBN abrasive grain and vitrified bond.

Abstract: In order to reduce the raw materials cost, lower the sintering temperature of 3Y-TZP optical fiber ferrules, the 3Y-TZP/ LAS glass ceramics composites were prepared and their properties were investigated in this paper. The results showed that the sintering temperatures and thermal expansion coefficients of the 3Y-TZP/LAS glass ceramics composites were lowered with the increase of glass content. The flexural strength of the composites were decreased with the increase of glass content, but the flexural strength of the composite with 15% weight glass was higher than 400MPa. The LAS glass powder added into the composites was crystallized and b-spodumene s.s was precipitated. during sintering. The b-spodumene s.s. having lower thermal expansion coefficient and higher strength was beneficial to reduce thermal expansion coefficients and keep higher strengths of the composites .