In situ transmission electron microscopy observation of the initiation and growth of microcracks in an SiC whiskerAl composite

The initiation and growth of microcracks in a SiC whisker (SiC_w)Al composite have been studied by means of the transmission electron microscope equipped with a tensile stage. It was found that microcrack initiation sources mainly included (1) the whiskers damaged and/or fractured during the preparation of the composite, (2) uninfiltrated zones, (3) SiC_wAl interfaces and (4) the matrix. Only the microcrack that nucleated in the matrix grew to become the major crack leading to specimen failure although many microcracks occurred in the early stages of straining. The whiskers and grain boundaries in the composite played an important role in impeding the growth of the cracks. When a crack was perpendicular to the frontal whisker, the crack tip would blunt near the longitudinal interface and it then advanced by bypassing the whisker end; when a crack was parallel to the frontal whisker, the crack would blunt near the whisker end and then propagated along the near-interface region of one side of this whisker.