Stress corrosion cracking (SCC) is a critical problem affecting the safety and viability of both existing energy conversion systems and ones under consideration for future development. In SCC, chemical interactions of a metal with the environment during corrosion accelerate degradation of materials under tensile applied stress, by reducing the critical stress intensity for crack propagation. Many competing mechanisms for the effect of corrosion in SCC have been put forth, including formation of brittle oxide or hydride phases, stress concentration at corrosion pits, and absorption of hydrogen. An additional mechanism is based on observed generation of tensile stress during corrosion of SCC-susceptible alloys (1,2). Corrosion-induced tensile stress would combine with externally applied stress to assist crack initiation and growth. Tensile stress may result, for example, from the lattice contraction due to vacancies produced by corrosion. This effect has been examined in the alkaline dissolution of Al, where lattice contraction is observed accompanied by extensive H absorption (3). The contraction was attributed to vacancies stabilized by association with hydrogen. In the same system, corrosion produces large concentrations of subsurface nanoscale voids, also revealing the presence of near-surface tensile stress (4).