Machinability Of Glass-ceramics Research Articles

Crystallization behavior and mechanical properties of high strength mica-containing glass-ceramics from granite wastes

The high-strength mica-containing glass-ceramics were prepared from granite wastes by bulk crystallization. The influences of SiO2/Al2O3 molar ratio (S/A = 7.72, 9.62, 12.58, 17.82 and 29.67) on the crystallization behavior, microstructure, mechanical properties and machinability of glass-ceramics were investigated. The results demonstrated that the polymerization degree of the glass network decreased with the S/A ratio increasing, which further caused the decrease in glass transition temperature and crystallization temperatures. The increase in the S/A ratio promoted the precipitation of diopside, hectorite, kalsilite and tainiolite in glass-ceramics when the samples were heated at 750 °C, while inhibiting the precipitation of forsterite. For the glass-ceramics crystallized at 800 and 900 °C, the main crystalline phases transformed from diopside, forsterite, and nepheline to diopside, kalsilite, and tainiolite, with the S/A ratio increasing. As the SiO2 gradually replaced Al2O3, the morphology of crystals changed from lamellar to granular, while the mean size of crystals reduced. The Vickers-Hardness values of glass-ceramics crystallized at 800 and 900 °C ascended with S/A ratio rising, and the values were above 6.30 GPa. The bending strength of most glass-ceramics is stable between 90 and 140 MPa, among which the maximum bending strength is 133.28 ± 14.81 MPa. The fracture toughness of the glass-ceramic crystallized at 800 and 900 °C declined, while that at 700 °C increased with a larger S/A ratio. Glass-ceramics after heat-treated at 900 °C with S/A ratio of 9.62 had the largest fracture toughness of 3.28 ± 0.15 MPa m1/2. In preliminary tests of machinability, glass-ceramic after heat-treated at 900 °C with S/A ratio of 9.62 showed better results.

Influence of NaF on Crystallization and Machinability of Mica Glass Ceramics

Effect of NaF on crystallization kinetics, microstructure, and mechanical properties of mica glass ceramics were investigated by the differential thermal analysis (DTA), X-ray diffractometry (XRD), scanning electron microscopy (SEM), and microhardness tests. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses are changed in the range of 235–246 KJ/mol, while the crystallization activation energies of samples with addition of NaF are changed in the range of 263–367 KJ/mol. The increase of crystallization temperature is helpful for the increase of aspect ratio, and the microstructure of the glass ceramics becomes interconnected, which contributes the improvement of the machinability of the glass ceramics. Microhardness (Hv), cutting energy (μ1), and machinability parameter (m) can be used for estimating the machinability of mica glass ceramics. Transparency in the studied glass samples is assumed to occur due to the presence of crystallites with nano size.

Effect of Fe 2O 3 addition on the sinterability and machinability of glass-ceramics in the system MgO–CaO–SiO 2–P 2O 5

The sintering and the crystallisation behaviour of a glass in the CaO–SiO 2–MgO–P 2O 5 system were studied by considering Fe 2O 3 as the nucleant agent. The addition of 5.0 wt.% Fe 2O 3 to the glass produces a sinterable glass-ceramic, with high relative density and mechanical strength. The glass-ceramic contains apatite, whitlockite and diopside phases at low temperatures and, in addition, wollastonite at high temperatures. The above-mentioned glass-ceramic has moderate machinability without onset of fracture.