Characterization of fracture toughness and micro-grinding properties of monocrystal sapphire with a multi-layer toughening micro-structure (MTM)

Abstract

The application of sapphire in micro-machining is often limited due to its high brittle feature. This study proposes and successfully fabricates a novel multi-layer toughening micro-structure (MTM) sapphire for improving its machinability in micro-grinding. A predicting model, which quantitatively predicts toughening effect Ujc, is built based on both toughening theory and regression method. The fabrication procedures of MTM sapphire with different micro-structures (LOCA& slots, only LOCA) are presented and LOCA by ultraviolet curing plays a vital role in this paper. Results from static tests of a fatigue testing machine show that MTM sapphires have particular fracture behaviors compared with normal monocrystal sapphire. The breaking force Fc is enhanced from 1.49kN to 7.29kN and 16.75kN. A central circle fracture and an annular breakage are observed, and all crack propagations are perpendicular to the annular breakage. A group of experiments to investigate the fracture behavior and toughening effects in micro-grinding of MTM sapphire are carried out by this study. The toughening effects in micro-surface grinding of MTM sapphire with large processing parameters are significant and big brittle fractures are reduced compare with normal sapphire. A damping effect is found in micro-grinding force of MTM sapphire, the amplitude and average value of micro-grinding force are all reduced comparing with normal sapphire, Fy shows the largest damping effect, the analytical coefficients of toughening effect are also given by this study. Finally, a micro-scale thin-wall (150μm width, 900μm depth, 2000μm length) is achieved by micro-grinding of MTM sapphire, it is demonstrated that the method which this study proposes successfully enhances the machinability in micro-machining of sapphire without harming its optical performance.