Review of surface factors in stress corrosion cracking of alloys

Abstract

From morphological observations of typical cracks in a susceptible system of wide practical interest, a number of distinctive features is pointed out and a comprehensive definition drawn for stress-corrosion cracking. Electrochemical mechanisms of crack nucleation at passive or relatively inert surfaces and subsequent subcritical propagation of nucleated cracks are outlined according to the most accepted models. Besides the number of surface factors involved in both stages, special theoretical consideration is given to the direct role played by surface energy in a growing crack. This is in relation to the highly active state of the metal at the crack tip (i. e. high tendency to release surface atoms) in front of the passive state of side surfaces. In the light of the mechanisms outlined, basic techniques are described for the experimental study of stress-corrosion cracking susceptibility.