A VACANCY/DISLOCATION INTERACTION MECHANISM OF TRANSGRANULAR STRESS CORROSION CRACKING E.I. Meletis and K. Lian Materials Science and Engineering Program Mechanical Engineering Department Louisiana State University Baton Rouge, LA 70803, USA ABSTRACT A transmission electron microscopy (TEM) study was performed to characterize the deformation substructure of two non-ferrous face-centered cubic metals tested for transgranular stress corrosion cracking (TGSCC). The experiments involved single-crystal specimens of α-brass and pure Cu tested under slow strain rate (lxlO" 6 s" 1 ) in 14 Ν NH 4 OH and 1M NaN0 2 aqueous solutions, respectively. The TEM observations in both materials showed a localized (more coplanar) deformation mode in areas just in front of the crack tip and a more homogeneous mode at larger distances (areas where there was no interaction with the environment). Based on the present TEM evidence and the previous phenomenology of TGSCC a "vacancy-dislocation interaction" process is described that has two major elements. First, it advocates that dissolution at slip steps produces subsurface vacancies that interact with dislocations promoting their motion and modifying their configuration. Second, it considers the vacancy diffusion in the region in front of the crack tip indicating the possibility of forming an extended "embrittled zone". Based on the present results and previous evidence a TGSCC mechanism is presented. INTRODUCTION The mechanism(s) of stress corrosion cracking (SCC) has (have) not been resolved yet, and this problem still remains of significant engineering concern and academic interest. Fundamental mechanistic aspects and advances in understanding this environment-induced failure have been addressed recently [1,2]. The common element in all of these brittle failure phenomena, regardless of differences or similarities in the operating mechanisms, is the embrittlement produced by a "stress/environment interaction". Of particular interest is the case of transgranular (TG) SCC of the otherwise ductile face-centered cubic (fee) metals and alloys since these materials have multiple slip systems and are characterized by high dislocation velocities. An important element of the underlying TGSCC mechanism is the crystallographic nature of cracking [3]. It has been shown in our 69