Research Of Cubic Boron Nitride (CBN) Matrix Ceramic Composite

Owing to high hardness, high strength and the other unique properties, CBN matrix ceramic composite is becoming one of the most potential tools in modern engineering applications. In this article, effects of additives, raw materials and preparation process on the properties of vitrified bond were studied. Surface treatment of CBN abrasive and preparation of microcrystalline CBN abrasive were also researched.The results indicated that Li2O was the most excellent element for decreasing refractoriness, and the following were CaF2 and ZnO. No obvious decreasing of refractoriness with addition of MnO2, whereas the refractoriness was increased with import of Fe2O3. Raw materials had notable effects on the performance of glass binder for CBN matrix ceramic composite. The results showed that the element in the form of carbonate was more beneficial to the refractoriness and fluidity of glass binder than that in the form of oxide. Moreover, if decomposition temperature of carbonate was lower, the mechanical property of specimens had no obvious difference with addition of carbonate or oxide. However, if carbonate was decomposed nearby the specimens'sintering temperature, the raw materials in form of carbonate did harm to improve the mechanical property of glass binder. Comparation between hydrate and carbonate, if decomposition temperature of hydrate was lower, raw materials in form of hydrate was more favorable to improve properties of glass binder than that in form of carbonate. Preparation processing had obvious influence on the properties of vitrified bond. The results indicated that premelting treatment was necessary for the glass binder with addition of carbonate. The porosity was reduced and the strength was increased with premelting processing.CBN abrasive particles were treated with acid or alkali and coated with low temperature glass coatings. The results were shown as follows: Acid treatment was beneficial to the single particle compressive strength, impact toughness and heat resistance of CBN abrasive grains. On the contrary, alkali treatment was harmful to the properties of CBN abrasive grains. CBN abrasive particles coated with low temperature glass coatings were compared with Ti coated CBN particles and corundum coated CBN particles. The results described that the sol-gel glass coating was excellent for oxidation protection of CBN abrasives because their beginning oxidizing temperature was higher about 100oC than that of uncoated CBN grains. The mechanical property of CBN abrasive particles was significantly increased with glass coatings. For the application of glass coated CBN abrasives to vitrified grinding wheels, it was evident that the glass coating provided high bonding strength between CBN abrasive grains and vitrified bond system.Microcrystalline CBN abrasive was prepared with ultrafine CBN powder as raw material and glass vitrified bond as binder sintering at pressureless processing. The results indicated that the microcrystalline CBN abrasive had dense structure and high strength. The property of the specimens was approaching to single crystal abrasive.