| Transgranular stress-corrosion cracking (T-SCC) in disordered Cu-25 at% Au single crystals was studied in 0.6 M NaCl and 0.13 M FeCl₃ solutions. This system is especially significant because cleavage-like fracture can occurqr in a normally ductile fcc system where the dominant surface process is de-alloying. De-alloying, i. e., selective dissolution of a less noble component, is believed to play an important role in embrittlement of Cu-25 at% Au during T-SCC. Therefore steady-state polarization, scratching, bending, zero imposed strain-rate tensile tests, and slow strain-rate tensile tests were carried out to establish the relationship between de-alloying and T-SCC. Under slow strain-rate loading, effects of potential and orientation on crack-propagation were also considered. The instantaneous and the average crack velocities were directly obtained by using the one-to-one correlation between current-transients/load-drop events resulting from discontinuous crack growth, and crack-arrest markings appearing on the fracture surface. Two independent methods using current transient or load-drop were used to obtain the values of the instantaneous and the average crack velocities. The result showed that the instantaneous crack velocity is faster than the average crack velocity by approximately three orders of magnitude. In addition, the instantaneous crack velocity is much faster than that expected by the slip dissolution model but much slower than that expected for brittle cleavage. |
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