The role of grain boundary structure and crystal orientation on crack growth asymmetry in aluminum

Abstract

Atomistic simulations have shown that the grain boundary (GB) structure affects a number of physical, mechanical, thermal, and chemical properties, which can have a profound effect on macroscopic properties of polycrystalline materials. The research objective herein is to use atomistic simulations to explore the role that GB structure and the adjacent crystallographic orientations have on the directional asymmetry of an intergranular crack (i.e. cleavage behavior is favored along one direction, while ductile behavior along the other direction of the interface) for aluminum grain boundaries. Simulation results from seven <110> symmetric tilt grain boundaries (STGBs) show that the GB structure and the associated free volume directly influence the stress-strain response, crack growth rate, and crack tip plasticity mechanisms for middle-tension (M(T)) crack propagation specimens. In particular, the structural units present within the GB promote whether a dislocation or twinning-based mechanism operates at the crack tip during intergranular fracture along certain GBs (e.g., the 'E' structural unit promotes twinning at the crack tip in Al). Furthermore, the crystallography of the adjacent grains, and therefore the available slip planes, can significantly affect the crack growth rates in both directions of the crack -this creates a strong directional asymmetry in the crack growth rate in the Σ11 (113) and the Σ27 (552) STGBs. Upon comparing these results with the theoretical Rice criterion, it was found that certain GBs in this study (Σ9 (221), Σ11 (332) and Σ33 (441)) show an absence of directional asymmetry in the observed crack growth behavior, in conflict with the Rice criterion. The significance of the present research is that it provides a physical basis for the role of GB character and crystallographic orientation on intergranular crack tip deformation behavior.

Critical assessment of hydrogen effects on the slip transmission across grain boundaries in α -Fe

“…The periodic boundaries (Y direction) were maintained with a separation distance of 12 nm between the boundaries. Several 0 K minimum energy GB structures were obtained through successive rigid body translations followed by an atom deletion technique and energy minimization using a nonlinear conjugate gradient method [42][43][44][45][46][47]. The GB energies were found to be in good agreement with previous studies [ were fixed for all the DGB cases examined here (figure 2a).…”

Atomic-scale investigation of triple junction role on defects binding energetics and structural stability in α-Fe

“…These GBs were characterized using the structural unit method [62,63]. As with past work [41,[64][65][66][67][68], an atom deletion criterion, multiple initial configurations and various inplane rigid body translations were utilized to accurately obtain an optimal minimum energy GB structure via the conjugate gradient energy minimization process. Circular wedges were then cut from the GBs along the stitch plane, i.e., {001}/{011} planes (see Figure 1a) [22,69,70].…”

Symmetric and asymmetric tilt grain boundary structure and energy in Cu and Al (and transferability to other fcc metals)

“…Many of the early studies (e.g., [5,6]) focused on understanding the grain boundary structure and energy. However, recent studies have expanded to address grain boundary sliding [7][8][9][10], migration and bulk dislocation slip transfer [11][12][13], grain boundary fracture [14][15][16] or spall [17][18][19][20], grain boundary segregation [21][22][23], phase transformations [24], grain boundary mobility [25,26], etc. In many cases, grain boundary structures have to be recreated in order to assess properties, and it is unclear whether the minimum energy structure was used or a higher energy metastable structure; hence, openly publishing grain boundary datasets in materials repositories can aid in providing a common starting configuration for these studies.…”