The role of grain-boundary structure in shock-induced spallation of molybdenum

Abstract

Grain boundaries and grain‐boundary ledge structures are shown to have a controlling influence on intergranular spallation in molybdenum resulting from shock‐wave rarefraction interactions. The structure of grain boundaries and their relationship to spall fracture are examined in detail utilizing the techniques of transmission and scanning electron microscopy, and are shown to be conducive to microcrack nucleation, coalescence, and propagation along the boundary planes. Grain boundaries possessing a high degree of complex structure such as dislocations and ledges are shown to vary significantly in effective dislocation density from the grain matrices, and this phenomenon coupled with the ability of ledges to nucleate cracks appears to account for intergranular spallation in molybdenum shock loaded to pressures of 150 and 250 kbar.