Nucleation of Slip Bands near Twin Boundary in High-Cycle Fatigue

Abstract

In order to investigate the criterion for the persistent slip band (PSB) formation near a Σ3(111) coherent twin boundary, where is a preferential site for formation of PSB, a highcycle fatigue test is carried out at room temperature using a copper bicrystal specimen with the twin boundary. PSBs are observed near the boundary in the connection with the evolution of extrusion/intrusion on the specimen surface. The slip behavior is different from that predicted by the Schmid factor. A finite element method (FEM) analysis is conducted for the bicrystal, and it reveals that the increase of resolved shear stress on the specific slip system due to the constraint of deformation between the crystals is the main cause for promoting the nucleation of PSB near the twin boundary. By taking into account the interaction between the primary and the secondary slip systems, it is possible to specify the formation behavior of PSB near the twin boundary.

Analysis of Stress Distribution in Au Micro-Interconnection by Polycrystalline Models

“…In other words, the Schmid factor represents the ratio τ rss /σ 0 far away from grain boundaries (dissimilar interfaces). Therefore, the local slip behavior in a small-strain should be described by the stress field under the deformation-constraint among the grains (6)- (8) . Hence, Fig.…”

“…Under small strain of a polycrystal, slip deformation and crack initiation can be described by the magnitude of τ rss /σ 0 (6)- (8) . Hereafter, we discuss τ mrss as the representative stress that governs the strength of the micro-interconnection.…”

“…Although the loading is homogeneous on the macroscopic scale, on the microscopic scale an inhomogeneous stress distribution is generated by the constituent grains in the interconnection. In the cyclic deformation of polycrystalline metals, the strain localization that induces crack initiation is governed by the elastic stress field due to the deformation anisotropy of the grains (6)- (8) . Thus, estimating the microscopic stress field is important for evaluating the reliability of the stacking LSI.…”

Mechanics of Fatigue Crack Propagation in Submicron-Thick Freestanding Copper Films

“…Most of the intrusions/extrusions observed in the experiments formed parallel to the Σ3 twin boundaries. Fatigue experiments performed on face-centered-cubic bulk metals with twin boundaries have demonstrated that persistent slip bands and subsequent intrusions/extrusions are preferentially formed at the slip system parallel to a Σ3 twin boundary [4][5][6][7]. This is due to stress concentration near the junction of a twin boundary and the surface, which is brought about by elastic mismatch between the crystals [6].…”

“…Fatigue experiments performed on face-centered-cubic bulk metals with twin boundaries have demonstrated that persistent slip bands and subsequent intrusions/extrusions are preferentially formed at the slip system parallel to a Σ3 twin boundary [4][5][6][7]. This is due to stress concentration near the junction of a twin boundary and the surface, which is brought about by elastic mismatch between the crystals [6]. In freestanding Cu films, such stress concentrations occur on the twin boundary edges, resulting in formation of the intrusions/extrusions.…”