Evidence for film-induced cleavage in rhodium plated nickel

Abstract

R. E. Ricker, J. L. Fink, J. S. Harris, and A. J. ShapiroMetallurgy DivisionNational Institute of Standards and TechnologyU.S. Dept. of Commerce, Technology AdministrationGaithersburg, MD 20899Introduction Transgranular stress corrosion cracking (T-SCC) is a form of environmentally induced subcritical crackgrowth which produces fracture surfaces that are cleavage-like in appearance. These fracture surfaces resemblecleavage because: propagation occurs on flat crystallographic facets, steps or ledges exist between the flat facetsforming river patterns, these facets and ledges match precisely on opposite sides of the fracture, andundercutting occurs at the ledges in the fracture surface. A variety of different mechanisms have been proposedto explain this form of crack growth, but no one mechanism is universally accepted. In general, the mechanismsthat have been proposed can be classified in two groups based on whether they assume that dissolution ormechanical fracture is responsible for crack growth.A dissolution mechanism for T-SCC needs to explain why dissolution is localized to the crack tip, why thefracture surfaces generated resemble cleavage and why opposite sides of the fracture surface match precisely (1).Even with these difficulties, dissolution based mechanisms attracted a number of advocates until Bertocci et al.(2) demonstrated that T-SCC cracks can propagate in a 70-30 α-brass exposed to a solution where Cu metal is inequilibrium with Cu