Crack growth under the effect of surface-active media

Abstract

On the basis of literature sources [1-6] it can be concluded that surface-active organic media facilitate the propagation of cracks in high-strength steels. However, there are insufficient data which make it possible to draw an ambiguous conclusion on the crack growth mechanism. In a number of studies, assumptions on the adsorption nature of this process are based on results of mechanical tests using a priori assumptions. Since the initial medium does not contain aerated water and does not cause dissolution and hydrogen charging of the metal, it is evident that the high rate of the effect of the interaction of the medium with the metal is caused by an adsorption process. However, this conclusion should be made on the basis of results of extensive investigations of the system by physicochemical analysis methods. Because of the absence of these results, some of the authors [7-9] dispute the possibilities of brittle fracture of materials exclusively as a result of adsorption of molecules of surface-active compounds (SAC) on these materials. It was concluded [7-9] that a reduction of the endurance of normalized 45 steel in lubricating mineral oils does not take place as a result of the adsorption effect but as a result of the electrochemical corrosive effect of impurities of aerated water and fatty acids on the metal. The possibilities of different crack growth mechanisms in dehydrated and moisture-containing media are indicated by the data [I0] according to which the subcritical crack growth process in a proton medium is caused by the adsorption-chemical interaction of molecules of the solvent with the metal of the crack tip. It was shown that in dimethylsulfoxide (DMSO) and water-dimethylsulfoxide media the molecules of the DMSO are efficiently chemisorbed on metals of the iron group and on steels. This phenomenon is reflected, in particular, in passivation of the freshly formed surface (FFS). In the presence of proton-donor particles in the DMSO, the kinetics of crack growth in the steel are determined by the simultaneous effect of two factors: hydrogen embrittlement and adsorption softening, with the first factor having a far stronger effect~