Fracture of polycrystalline silicon

The present work investigates the fracture behavior of polycrystalline silicon grown by chemical vapor deposition. The critical stress intensity factor, KIc, was measured using disk-shaped compact tension specimens with non-zero crack tip radii. Grain size effects and the effects of crack plane orientation and crack propagation direction were investigated with respect to microstructural texture. Fracture tests were performed at temperatures ranging from 25 to 1075 °C to identify a transition in toughness with temperature, and complete fracture toughness measurements were made at room temperature and 925 °C. Fracture surface analysis was performed to identify changes in fracture mode associated with increased temperature. There were only minor changes in critical stress intensities with respect to microstructure for material tested at room temperature. KIc increased from 1.5 to 1.8 MPa m1/2 at room temperature to 3.3 MPa m1/2 at 925 °C, which was associated with a change in the roughness of the fracture surface. There was no evidence of ductile fracture found even at the highest test temperature of 1075 °C.