Study of Serrated Boundary Micromechanics During Micropillar Compression in Nickel-Based Superalloy

Abstract

This study reports the interplay between grain boundary morphology and mechanical behaviour using micropillar compression. Quantitative findings indicate that serrated grain boundaries with multiple curvatures exhibit notably higher yield strengths compared to their straight counterparts. In a bi-crystal system, 18 pct increase in boundary length, achieved through multiple curvature boundaries, results in 21 pct increase in yield strength. The quasi-in-situ electron backscatter diffraction (EBSD) investigations show the concentration of plastic strain within preferentially oriented slip bands, with grain boundaries offering resistance, and slip band leads to changing directions as they traverse from one grain to another, with secondary slips emerging post-yielding during micropillar compression. As compression levels rise, a prominent uniform strain hardening rate emerges in grain boundaries characterized by multiple curvatures. Local resolved shear stress at grain boundaries experiences a pronounced reduction under the applied load, particularly when the serration wavelength exceeds 0.4, and the amplitude ranges from 0.3 to 0.5 times the total grain boundary length. An attempt is made here to shed light upon the underlying microscopic mechanisms that govern grain boundary micromechanics through a comprehensive three-dimensional analysis. It becomes evident that both boundary curvature and inclination of interface plane play critical roles in enhancing material strength, collectively contributing to a 21 pct increase in yield strength in current case of boundary with curvature. Additionally, these morphologies notably reduce the likelihood of heterogeneous plastic deformation compared to straight grain boundaries.