Defect Structure of WC Deformed at Room and High Temperatures

Single crystals of WC, deformed by micro-indentation at room temperature and at 1000°C, are examined by transmission electron microscopy in order to determine the mechanism of slip. The plastic deformation induced by indentation occurs by the motion of partial dislocations with Burgers vectors 1/6 $$ \left\langle {11\bar 23} \right\rangle $$. These partial dislocations combine in pairs to form extended dislocations with Burgers vectors 1/3 $$ \left\langle {11\bar 23} \right\rangle $$. Deformation in samples indented at 1000°C takes place by the same mechanism.Reactions occur between the leading partial dislocations of faults on intersecting slip planes. The new partial dislocation formed at one of these intersections is shown to have Burgers vector 1/6 $$ \left[ {1\bar 210} \right] $$, This reaction causes the defect configuration to became sessile and may be the first step in a crack nucleation mechanism similar to that proposed by Cottrell for bcc metals. The observation of defect pile-ups at tips of microcracks formed near room temperature, high load (500 gm) indentations, supports this suggestion. A high density of defects found near the cracked edge of a specimen indicates that plastic deformation may accompany crack propagation under some circumstances.