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

Abstract

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 μm 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-μm-wide specimens, whereas intrusions/extrusions were observed in 2-μm-wide specimens, leading to crack initiation. Vein-like structures comprising edge dislocations were observed in 5-μm-wide specimens, which are commonly observed in bulk metals. Conversely, the dislocation structure in 2-μm-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.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 μm 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-μm-wide specimens, whereas intrusions/extrusions were observed in 2-μm-wide specimens, leading to crack initiation. Vein-like structures comprising edge dislocations were observed in 5-μm-wide specimens, which are commonly observed in bulk metals. Conversely, the dislocation structure in 2-μm-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.