Influence Of Complex Fluxes On The Performance Of LAS Glass-ceramic Diamond Composite

Diamond composites were widely used. In this study, the performance of Li₂O-Al₂O₃-4SiO₂ (LAS) glass-ceramic were optimized by introducing complex fluxes (B₂O₃, Na₃AlF₆, Na₂O), a new kind of diamond composite was developed with this glass-ceramic bond. The influence of single component, bi-component complex fluxes, tri-component complex fluxes on the thermo dynamical parameters, crystallization properties, chemical stability, coefficient of thermal expansion (CTE) of glass-ceramic bond were investigated through differential thermal analyzer (DTA), x-ray diffraction (XRD), scanning electron microscope (SEM), three-point bending strength tester and so on. The experimental results show that:1)It is not feasible to obtain high strength diamond composite via adding single fluxing agent when samples were sintered below 800℃. The refractoriness of raw materials cannot drop below 750℃when additive amount of single fluxing agent is very small, but performance of glass-ceramic bond is poor when additive amount is too much.2)When bi-component complex fluxes were added, AlSi6.84BO18 crystals would form in glass-ceramic when the ratio of B₂O₃ in bi-component complex fluxes (B₂O₃-Na₃AlF₆) was 9%. Excessive Na₃AlF₆ (exceed 6%) would be harmful to the stability of glass system and result in uncontrolled crystallization. If additive amount is adequate, Na₃AlF₆ would be broken down into F- which could react with MgO and form MgF2 When raw material were molten at 1400℃. Tetragonal MgF2, which has a similar crystal structure asβ-spodumene but different crystal structure withβ-quartz, could firstly separate out as nucleating agent during heat treatment process. This nucleating agent could promote the formation ofβ-spodumene but hinder the formation ofβ-quartz.3) When tri-component complex fluxes were added, Nephelite, which had high coefficient of thermal expansion (CTE), would generate when the amount of Na₂O in parent glass is more than wt.3%. The homogeneity of microcrystal's properties, size and form is crucial factor to bending strength. Complex fluxes with a reasonable ratio of B₂O₃, Na₃AlF₆ and Na₂O could efficiently reduce melting point and crystallization temperature, meanwhile, the adverse impact of fluxes on the performance of initial glass could be minimized. 4) Crystallization temperature could affect the crystalline form, crystalline size and crystallinity, High crystallization temperature benefits high crystallinity,high strength and low CTE, and promote crystal transfer ofβ-spodumene from granulated crystal to needle-like crystal.At last, the best additive amount and ratio of complex fluxes was determined, that is, total additive amount of complex fluxes is 15%, the best ratio of B₂O₃, Na3AlF6, Na2O is 6%:6%:3%. Nucleated at 630℃/2h and then crystallized at 760℃/2h, the CTE of this kind glass-ceramic bond is 3.08×10-6/℃,which is close to that of diamond. LAS glass-ceramic bond diamond composite with high bending strength (81.3Mpa) was obtained when sintered as heat treatment schedule above. This kind of glass-ceramic bond has matched properties with diamond grains and meets the requirement of high-speed diamond composite.