純銅単結晶のＮａＮＯ２溶液中における応力腐食割れ

Abstract

The Crystallography of transgranular stress corrosion cracking (SCC) in pure copper single crystals was studied by scanning electron microscopy. The regular prismatic specimens oriented for [001], [101], [111], [112], [213] and 0.50 in Schmid factor were prepared, and they were SCC-tested in 1kmol·m-3 NaNO2 solution at room temperature by slow strain rate technique. The fractographic results showed that many cracks nucleated from the specimen surfaces with frequent slip-steps, producing a black turnish film. The susceptibility to SCC estimated from the nominal stress-strain curves increased markedly in the [101]- and [111]-oriented specimens. Most of the fracture surfaces showed the characteristic of river-like pattern, which was formed by the crack growth along ‹110› direction on {110} plane. The appearance of {111}-‹112› type was also observed partly in the initial stage of crack growth. It was found that the crack growth of {110}-‹110› type was strongly controlled by the normal stress to {110} plane which takes the smallest angle with respect to tensile axis.