Abstract

Although widely used for the characterization of grain boundaries within the coincidence site lattice (CSL) [1] framework, the application of Brandon’s criterion [2] for allowable angular deviation (i.e., Du # 15 S degrees), has often resulted in grain boundaries which do not display ‘special’ behavior being classified as low-S CSL’s; thus prompting some debate as to the overall validity of the CSL model. Other more restrictive criteria have previously been proposed; all of which being based upon the low angle approximation of the Read-Shockley relation [3], u'b/d, where u is the misorientation angle, b is the magnitude of the Burgers vector of grain boundary dislocations, and d is the dislocation spacing. The criterion of Ishida and McLean [4] considers a S dependence for Du based upon b being proportional to the two minimum Burgers vectors of the DSC lattice (i.e., S) [5], and the minimum dislocation spacing, d, being proportional to the boundary plane periodicity for symmetrical tilt grain boundaries (i.e., S). Deschamps et al [6], in attempting to generalize the criterion to all grain boundaries (i.e., symmetrical and asymmetrical tilt, twist) proposed a S dependence by considering a dislocation spacing (d) proportional to a mean edge (p) of the CSL lattice [5] (S) and a Burgers vector magnitude (b) varying on average as the mean edge of the DSC lattice [5] (S). Palumbo and Aust [7] showed that since the third Burgers vector of the DSC lattice is independent of S [5], b can only vary as S; this yielding a S dependence for the maximum allowable angular deviation. Early experimental support for the Palumbo-Aust criterion [7], Du # 15° S, was obtained by (1) a review of transmission electron microscopy studies [8] for the resolution of discrete intrinsic grain boundary dislocations [9], and (2) controlled electrochemical etching studies conducted with high purity Ni in sulphuric acid media [7]. More recently, Pan et al [10] demonstrated that Brandon’s criterion was not applicable in discerning crack-resistant grain boundaries in alloy X-750; however, in this study [10] grain boundaries classified as CSL’s using the more restrictive Palumbo-Aust criterion were indeed found to display ‘special’ cracking-resistant behaviour. With recent advances in automated electron backscatter diffraction techniques [11] and the emergence of commercial applications for ‘grain boundary engineered’ materials [12, 13], the structureproperty database upon which to evaluate the applicability of these criteria for ‘special’ behaviour has been expanded significantly. In this work, the relative applicability of the widely used Brandon criterion and the more restrictive Palumbo-Aust criterion is investigated by evaluation of experimental results pertaining to the corrosion, cracking, and creep cavitation susceptibility of several commercial metals Pergamon Scripta Materialia, Vol. 38, No. 11, pp. 1685–1690, 1998 Elsevier Science Ltd Copyright © 1998 Acta Metallurgica Inc. Printed in the USA. All rights reserved. 1359-6462/98 $19.00 1 .00 PII S1359-6462(98)00077-3

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