Transition from brittle fracture to ductile behavior in 4H–SiC

The four-point bend test was used to measure the brittle-to-ductile transition (BDT) temperature in precracked samples of semi-insulating 4H—SiC at four different strain rates. As in other semiconductors, the BDT temperature T_BDT was found to be very sharp, within ±15 °C, and to shift to higher temperatures with increasing rates of the applied load (or strain rate). The results appear to be consistent with a transition temperature T_c recently observed in the yield stress of the same material as measured by compression experiments. However, strain-rate measurements in four-point bend tests are not strictly equivalent to those in compression experiments, and therefore it is difficult to directly compare the measured BDT temperatures with the yield stress transitions. Nevertheless, it is believed that the reasonable agreement between T_BDT and T_c supports the model recently proposed to explain these transition temperatures.