Basic criterion for the formation of self-organized dislocation patterns in fatigued FCC pure metals

Abstract

tively proposed based on stacking fault energy (SFE).As shown in Fig. 1, PSB ladders or walls are a three-dimensional structure. PSB ladders from t he (12 − 1) plane or PSB walls from the (111) plane occupy about 10% of the PSBs by volume. The walls are 0.03-0.25 μm in thickness with a spacing of about 1.3 μm (see Fig. 2) and they consist of numerous dipoles, especially faulted dipole. The socalled faulted dipole consists of four Shockley partial dislocations and three stacking faults. Th e stair-rods lie at the ends of the stacking fault in the secondary slip plane and their relative position are thus fixed. The dipole as a whole can assume an S-or Z-shaped configuration depending on the position of the Shockley partials. In 1976, Antonopoulos et al. [11,12] pointed out that the matrix vein contained both primary edge dipole and faulted dipole, however, the PSBs were almost full of faulted dipoles, which reflected the microstructure evolution of dislocation patterns. On Based on a large number of experimental results available, it is found that not all the fatigued face-centered-cubic (FCC) pure metals can form the classical persistent slip band (PSB)-ladder structure. The formation of the regular dislocation patterns, especially the PSB ladders, follows one unified principle on the dislocation aggregation and evolution. According to the principle, a simple criterion based on stacking fault energy is proposed to judge whether or not the regular PSB ladders in different FCC pure metals can form.

Intrinsic high cycle fatigue behavior of ultrafine grained pure Cu with stable structure

“…The damage morphology of SPD Cu is very different from that in FSP Cu observed in this study [3][4][5][6][7][8][9][10]. It is well known that large-scale slip bands, several tens of micrometers in size have been observed on the damaged surfaces of SPD Cu, even at very low stress amplitudes (less than 0.5 UTS) [4,5,7,10,31]. Furthermore, Goto et al [32] indicated that the slip bands formed in ECAP Cu were longer and had an inferior uniformity of distribution density at a lower stress amplitude of 120 MPa, when compared to the slip bands at a high stress amplitude of 240 MPa.…”

“…Moreover, many extrusions can be observed protruding from the slip bands, as shown in Fig. 3b, which is similar to that of the single crystal Cu [28,31]. For FSP Cu, no large-scale slip bands could be observed, and no obvious crack initiating sites were found near the fracture edge.…”

Standing wave effect and fractal structure in dislocation evolution

“…2 , based on the standing wave effect, the capture of edge segments at the nodes shows that the dislocation loops are bowed out along both sides of the ladders at equal intervals, thus its interval distance is the same as the ladder thickness d w . Meanwhile, the mean interval distance of edge dislocation in the ladders is approximately 8 times as long as the extended dislocation width d ex 33 . Considering Shockley partials in pairs, substituting and into Eq.…”