Micro-toughness of ZrB₂-based ceramics evaluated by ultra-shallow V-notch

Because of the essential difference between micro-toughness and macro-toughness, the indiscriminate application of deep notch tests may result in serious errors of micro-toughness associated with shallow cracks or flaws in ceramics. Here, the micro-toughness values of ZrB2, ZrB2-SiC and ZrB2-SiC-Grapite ceramics were successfully measured through ultra-shallow sharp V-notches (depth less than 40 μm, the ratio of notch depth to sample height less than 0.01) produced by nanosecond laser on the surface of bending bars for the first time. Results indicated that the micro-toughness values obtained from these three typical ceramics were significantly lower than the macro-toughness values measured from deep notches. Furthermore, conflicts may arise when comparing the micro- with macro-toughness between different materials, such as the macro-toughness of ZrB2-SiC-G was larger than that of ZrB2-SiC, while a contrary result was obtained for micro-toughness. Compared with the indentation method, improved accuracy of micro-toughness measurement could be obtained by this method.