Dynamic Fracture And Dealloying Induced Stress-Corrosion Cracking

Electrochemical dealloying is a corrosion process in which one elemental component of an alloy is selectively dissolved often resulting in the evolution of a bicontinuous nanoporous morphology composed of ligaments and pores. When such structures form on the surface of ductile face-centered cubic metals such as brass, stainless steels and gold-containing alloys, it has been proposed that they trigger stress-corrosion cracking as a result of their ability to support high-speed cracks that can be injected into the undealloyed parent phase alloy. Here we examine how the applied stress or stored strain energy control the dynamics of high-speed crack propagation and the relationship between the fracture plane orientation of cracks that have been injected into the undealloyed parent phase and that which forms during stress corrosion cracking of a single-crystal silver-gold alloy. In both cases, we observe exceptionally flat cleavage-like fracture surfaces, whose crystallographic orientation is determined by that of the tensile axis. We present a continuum formulation of the injection distance based upon a crack tip equation of motion that incorporates inertial effects in which the work of fracture is a decreasing function of crack speed.