Fracture surfaces were studied in a scanning electron microscope (SEM). The surfaces were coated with a thin gold layer in a Blazers SCD050 sputter coater. The SEM was a Cambridge Camscan SH-80D operating at accelerating voltage of 20 kV. Optical microscopy was performed with a built-in microscope of a Matzusawa MXT-α microhardness tester connected to a computer for image analysis.