Observation of the Formation Process of Fatigue Dislocation Structure in Micro-sized Ni Single Crystal

Abstract

The purpose of this study is to diretly observe the formation process of characteristic fatigue dislocation structure in micro-sized nickel (Ni) single crystal specimens with a single slip orientation. Dog-bone shaped specimens with a cross-sectional area of 2 μm×2 μm were prepared by means of a focused ion beam processing system. Although tension-compression cyclic tests under a constant stress amplitude were performed on them, they were interrupted after different cycles (N = 1, 100, 1000 and 3500) and the inside was observed by a UHV-TEM after thinning. In the early stage of the test (N = 1 and 100), dislocations were rapidly multiplied. After N = 1000 where intrusions/extrusions appeared on the specimen surface, the dislocations gathered at the local areas. Then dislocation walls like those observed in a ladder-like structure in PSB was formed after N = 3500 cycle. This implies that vein, which is the important dislocation structure in fatigued bulk material, cannot be formed in micro-sized metals due to the tiny dimension.