Surface Relief Formation of Cyclic-Loaded Coarse-Grained Aluminum Polycrystals with Point Defect Clusters

抄録

Surface relief formation processes of the high cyclic-loaded coarse-grained aluminum polycrystals with point defect clusters were investigated. Until the loading of 1 × 10⁵ cycles with the stress ratio of −1 and the maximum stress of 8.0 MPa, the coarse ribbon-like primary persistent slip markings (PSMs) consisting of extrusions and intrusions had been formed, and the average extrusion height of the PSMs had reached 2.0 µm. This value was much higher than that of the ordinary aluminum single crystal. The high mobile dislocation density accompanied by the dislocation channeling effect inside the persistent slip bands (PSBs) were considered to produce the high extrusions. Until the loadings to 2.4 × 10⁵ cycles with the stress ratio of −1 and the maximum stress of 8.0 MPa, activities of the primary PSBs had been weakened or terminated, and instead, the secondary slips had been activated and deformed the shapes of the preexisting primary PSMs. And the deep brittle-like cracks along the grain boundaries (GBs) were observed. The accumulation of the dislocations and the vacancies into the GBs were considered to be the trigger for the energy reduction of the GBs as the interfaces and the brittle-like cracks formation.

Fig. 16 (a) SEM image showing the deep brittle-like crack observed after the loading of 2.4 × 10⁵ cycles with the maximum stress of 8.0 MPa at the GB between “Grain C” and “Grain D”. (b) Enlarged image of the crack. A huge number of faint PSMs were intersecting with the GB where the crack opened.