Advanced ceramics, such as alumina and zirconia, are widely used in modern industries, due to their superior properties, such as high hardness and strength. Fracture toughness is a significant property that describes the capability of materials to resist crack instability and expansion to failure, and also helps when calculating the allowable working stress, and crack size, of the component. This paper comprehensively lists the current toughness-testing methods. With comparative investigations of various methods, edge chipping is found to be the simplest way of measuring the ceramic fracture-toughness, in terms of the dominant median crack, chip geometrical similarity, and force-distance relations, giving consideration to its potential application in industry. Moreover, to avoid the data variance from crack-length measurement in edge chipping, it is further proposed that the energy analyses can be used to improve the way in which the toughness expression is formulated.

Overcoming the low fabricating efficiency of traditional chemical mechanical polishing (CMP) for Gallium nitride (GaN) is a challenge owing to its high hardness, high brittleness, and chemical inertness. Here, electrochemical etching is proposed to increase the material removal rate and acquire a high-quality surface on GaN wafers. To reveal the synergistic etching mechanism of oxidizing agent and corrosion inhibitor on the GaN wafers, electrochemical etching experiments were carried out. The optimal etching solution contained 4 wt% H ₂ O ₂ and 10 mmol l ⁻¹ purified terephthalic acid. Experiments with various polishing parameters were comparatively investigated to verify the auxiliary effect of etching and determine the ideal parameters. Cathodoluminescence spectroscopy shows that the electrochemical etching removes the SSDs completely and the CMP process with befitting parameters does not induce supernumerary SSDs.