SCRATCHING AND GRINDING OF A MACHINABLE GLASS-CERAMIC WITH WEAK INTERFACES AND RISING T-CURVE

The scratching and grinding response of a machinable mica-containing glass-ceramic is examined relative to the base glass. The influence of weak interfaces and a rising toughness curve (T-curve) on machinability and damage modes is investigated. A profound manifestation of these characteristics is a change in the nature of subsurface damage from macroscopic fracture in the base glass to distributed microfracture in the glass-ceramic. As a result, the mechanism of material removal changes from extension of macrocracks in the base glass to microfracture and dislodgement of the mica grains in the glass-ceramic. High removal rates in scratching compare with low forces in grinding of the glass-ceramic. The removal rates and the grinding forces are found to correlate with the short-crack toughness instead of the conventional long-crack toughness. Abrasive machining of ceramics possessing weak grain boundaries and interfaces and associated rising T-curve behavior is discussed in light of these results.