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In this study, a series of friction tests on semimetallic automotive friction materials were conducted on a friction test machine by pressing test samples against a rotating cast iron brake disc, thus simulating actual braking. After each friction test, the morphological changes of the wear surface and subsurface were investigated using scanning electron microscopy. Microstructural examinations showed that the major wear mechanisms in operation during braking are comprised of the following: (i) abrasive, (ii) adhesive, (iii) fatigue, (iv) delamination, and (v) thermal. The wear mechanism and wear transition are found to be influenced by the applied loads and braking times. In the study of the subsurface morphology, microcracks generated in the subsurface are thought to be due to the following phenomena; (i) growth of microvoids, (ii) coalescence of microvoids, (iii) coalescence of second phase particles, and (iv …