In situ measurements of a homogeneous to heterogeneous transition in the plastic response of ion-irradiated 〈1 1 1〉 Ni microspecimens

Abstract

We report on the use of quantitative in situ microcompression experiments in a scanning electron microscope to systematically investigate the effect of self-ion irradiation damage on the full plastic response of h1 11i Ni. In addition to the well-known irradiation-induced increases in the yield and flow strengths with increasing dose, we measure substantial changes in plastic flow intermittency behavior, manifested as stress drops accompanying energy releases as the driven material transits critical states. At low irradiation doses, the magnitude of stress drops reduces relative to the unirradiated material and plastic slip proceeds on multiple slip systems, leading to quasi-homogeneous plastic flow. In contrast, highly irradiated specimens exhibit pronounced shear localization on parallel slip planes, which we ascribe to the onset of defect free channels normally seen in bulk irradiated materials. Our in situ testing system and approach allows for a quantitative study of the energy release and dynamics associated with defect free channel formation and subsequent localization. This study provides fundamental insight into the nature of interactions between mobile dislocations and irradiation-mediated and damage-dependent defect structures.

Stainless Steel 304 Micro-pillar Mechanical Response to Ion Irradiation and Helium Implantation Under Transmission Electron Microscopy Observation

“…Load drops in the stress strain curves were only evident in the pillars that were irradiated with Kr Ions, especially the pillars that were pre-implanted with helium. The presence of load drops in irradiated stress strain curves of micropillars has been found in other papers [8] and they are speculated to be associated with defect free channels. Snap shots of the 1×10 17 He ion/cm 2 pillar over various strains with its accompanying stress strain curve is shown in Figure 2.…”

Manipulation of free volumes in a metallic glass through Xe-ion irradiation

“…The representative stress-strain curves are plotted in Fig. 3(c), exhibiting an initial elastic deformation, followed by the jerky-flow behavior manifested by several load drops [49]. The jerky flows are attributed to shear banding [15].…”

“…3(c)]. Accordingly, we can image that if the ion irradiation can modify the critical shear-avalanche value to be as low as possible, the intermittent shear-avalanche can be avoided, and the homogeneous plastic deformation can be consequently achieved [49].…”

A tale of two mechanisms: Strain-softening versus strain-hardening in single crystals under small stressed volumes

“…For ductile metallic materials, sample preparation and prior thermomechanical treatment usually introduce at least a moderate density of dislocations, and the material strength is governed by the evolution of the dislocation microstructure through a variety of nucleation, propagation, and multiplication processes [4]. A multitude of small scale mechanical experiments have been conducted in recent years to understand the size-dependence of the material strength, which will ultimately bridge the above theoretical strength limit and the bulk flow limit [5][6][7][8][9][10][11][12][13][14][15][16]. Experimental efforts using micro-pillars machined by focused ion beam (FIB) are mainly focused on searching the scaling relationship between the yield strength and the pillar diameter [5][6][7].…”