Multi-Probe Characterization of Plasticity Heterogeneity: Requirement of Alloy Design Considering Dislocation Planarity for Developing Crack-Resistant Ni–Cr Alloys

抄録

Ni–20Cr alloy is a representative model alloy that shows planar dislocation motion. The planar dislocation motion causes plasticity-induced stress concentration at grain boundaries, which can be a reason for intergranular cracking. In this study, the micro-deformation behavior in Ni–20Cr alloy and its interaction with grain boundaries were investigated. To clarify the micro-plasticity near grain boundaries in Ni–20Cr alloy, we present an applicability of the in situ electron channeling contrast imaging (ECCI) method coupled with in situ micro-deformation analysis, digital image correlation (DIC), and post-mortem electron backscatter diffraction (EBSD). The in situ multi-probe microscopy showed planar dislocation pile-up and local dislocation accumulation, which caused local stress concentration at the grain boundaries. The degree of plasticity-enhanced stress concentration appeared most distinctly near grain boundary triple junction. This result is consistent with previous studies that reported brittle-like cracking can preferentially occur at the grain boundary triple junction. That is, the plasticity-enhanced stress concentration can play a role in brittle-like intergranular cracking that occurs after significant plastic deformation under some special conditions such as hydrogen environment.

Fig. 1 (a) In situ tensile test curve, and ECC images at the strains of (b) 0%, (c) 0.08%, (d) 0.15%, (e) 0.37%, and (f) 0.43%. The planar dislocation arrays are marked with yellow dashed lines. The small arrows in (c) indicate a newly formed dislocation planar array. The inset in (c)–(f) indicates the magnification of the highlighted region for each step that show the pile-up of dislocations. The video file is also uploaded as the supplemental material.