Dealloying parting limit

Percolation concepts Percolation concepts of dealloying are based on the association of sharp parting limits with the abrupt occurrence of connected paths of the fast-dissolving component, when in a random solid solution the concentration of that component is being increased. Early approaches of this idea made use of probability calculus to determine the fraction of chains of the less noble component in dependence on the alloy composition. For infinite chain lengths, the results were sharp composition thresholds that varied with the chain multiplicity and were associated with Tammann s parting limits for environments with different oxidative... 

More recently, percolation theory and computer simulation of the dissolution process was applied. This latter approach resulted in 2D and 3D percolation thresholds (that is, composition thresholds at which infinite connected paths of the fast dissolving component were formed) as well as in images of the atomic scale disorder induced by dealloying. 3D site percolation thresholds 20 at.% in a fee lattice), leading to an infinite connected cluster of nearest neighbors of less noble atoms, were considered to correlate with the absolute parting limits of alloys with high such as... 

In some alloy systems, studies of dealloying appear to show a "parting limit. ASTM defines parting limit as ... 

Solid solution composition classically controls the SCC of brasses [71,72], austenitic stainless steels in hot chloride solutions [73,74], and noble-metal alloys [75]. In all these systems there is evidence that dealloying dominates the SCC mechanism, although this remains controversial for stainless steels. Transgranular SCC ceases above a critical content (parting limit or dealloying threshold) of the most noble alloying element, either 80-85% in Cu-Zn or Cu-Al or 40% in Ni-Cr-Fe or Au-X alloys (Figures 11.9 and 11.10). These values... 

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