Dislocation structures in micron-sized Ni single crystals produced via tension-compression cyclic loading

The strength and deformation characteristics of micron-sized metals under monotonic loading have long been investigated. In contrast, despite its practical significance, their fatigue behavior remains unexplored. To this end, tension-compression fatigue tests were conducted herein on micron-sized Ni single crystals to elucidate their fatigue behavior and internal dislocation structures. Specimens with square cross sections of 5 and 2 mu m on a side were prepared and subjected to cyclic loading at low stress amplitudes, which did not induce fatigue cracking in bulk metals. Remarkably, fatigue cracks were not present in 5-mu m-wide specimens, whereas intrusions/extrusions were observed in 2-mu m-wide specimens, leading to crack initiation. Vein-like structures comprising edge dislocations were observed in 5-mu m-wide specimens, which are commonly observed in bulk metals. Conversely, the dislocation structure in 2-mu m-wide specimens resembled that associated with persistent slip bands, which cause intrusions/extrusions and fatigue cracking in bulk metals under high stress amplitudes. The experimental findings indicate that the fatigue behavior of small-sized metal single crystals is characterized by the absence of vein formation.