ON THE ENERGETICS OF DISLOCATION EMISSION FROM A CRACK-TIP IN NICKEL-CONTAINING HYDROGEN

被引:18
作者
HOAGLAND, RG
机构
[1] Department of Mechanical and Materials Engineering, Washington State University, Pullman
基金
美国能源部;
关键词
D O I
10.1557/JMR.1994.1805
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
A method that determines the work done in shearing atom pairs straddling the slip plane, PHI, during emission of dislocations from a crack tip in an atomic model is presented. The model is based on an EAM-type potential for nickel. The dislocations are emitted as partials, and the disregistry, DELTA, across the slip plane is found to be fit accurately by a simple arctan function of position for each partial. The width of the partials is also found to remain essentially constant as they are emitted and move away from the crack tip. Rice's unstable stacking energy is extracted from the PHI - DELTA curves for the atom pairs along the slip plane and is observed to vary somewhat, particularly near the crack tip. In addition to the PHI(DELTA) at points on the slip plane, the total work done on the entire slip plane is determined as a function of the dislocation position in the spirit of the Peierls approach. The derivative of this total work with respect to dislocation position leads to the lattice resistance, sigma(r). The first partial dislocation to be emitted experiences a maximum in sigma(r) at about 0.2 nm from the crack tip, and several contributions to the overall resistance can be identified including the creation of a new surface at the tip as emission occurs, the creation of stacking fault as the dislocation glides away from the tip, and a small but discernible periodic component with a period related to the lattice. A string of hydrogen interstitials is introduced at various locations in the lattice and its effect on DELTA, the PHI - DELTA curves along the slip plane, and the lattice resistance is examined. A substantial effect on the unstable stacking energy results as the dislocation passes an interstitial on the slip plane, but the effect of an interstitial on the resistance to dislocation emission expressed in terms of the maximum sigma(r) is small and then only if it is confined to a region very near the crack tip. The significance of these results is discussed together with some additional observations including dislocation pinning on the interstitials.
引用
收藏
页码:1805 / 1819
页数:15
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