Low melting temperature machinable glass ceramics

Traditional mica glass ceramics have excellent machinability, but they show relatively poor mechanical strength that restricts their applications in many load-bearing situations. Much work has been done in improving the strength of these mica glass ceramics. Although high melting temperature glass ceramics have greater strength, the high processing temperature makes the preparation process difficult. Low melting temperature glasses have attracted the attention of many researchers, but their strengths are correspondingly low. In this study, B₂O₃, Li₂O, and ZnO were added to the glass composition so as to decrease the melting temperature of the glasses. A melting temperature of 1240°C was achieved in this study. The effect of heat-treatment process on the microstructure of glass ceramics was studied with the aim of increasing the glass strength while maintaining good machinability. It was found that glass ceramics heat-treated with a novel multistep heat-treatment process, 520°C for 1 h + 600°C for 1 h + 730°C for 2 h, provided the optimum combination of properties, including good machinability (drilling speed of 4-6 mm/min) and relatively high mechanical strength (bending strength 183 MPa).