Grain Boundary Fracture of α Brass Bicrystals at an Intermediate Temperature Range

Abstract

Deformation and grain boundary fracture behaviours of α brass bicrystals were examined. The results are summarized as follows:
(1) The temperature dependence of the ductility of α brass bicrystals accompaning intergranular fracture is similar to that observed in α brass polycrystals.
(2) The transition from transgranular to intergranular fracture starts at about 470 K and again a transgranular fracture appears at about 770 K: i.e., the intergranular fracture occurs in the temperature range of 470 to 770 K. It is note worthy that the lower transition temperature (470 K) corresponds to the onset of the inverse temperature dependence of yield stress. Also, the temperature at which the minimum value of ductility reveals coincides with that at which a peak in the yield stress appears.
(3) Though the intercrystalline fracture accompanies the separation at the grain boundary plane macroscopically, it is a ductile fracture in the neighbourhood of grain boundary microscopically. Thus, apparent intergranular fracture seems to be caused by the coalescence of micro cleavage cracks along {111} planes, which are induced by the stress concentration due to dislocation pile-ups.
(4) From those observations mentioned above, it is clear that the dynamic strain aging behaviour plays an important role in the intergranular fracture of α brass bicrystals.