Twin boundaries as crack nucleation sites

Abstract

Coherent twin boundaries (TBs) in f.c.c. metals are considered to have low energy. Nevertheless, even TBs are preferred sites for crack nucleation in materials loaded at very small alternating plastic strain amplitudes (high cycle fatigue). In the present paper, the mechanism of short crack propagation starting from TBs was studied for medium amplitudes and described taking into account both elastic and plastic anisotropy effects. A strong dependence of the TB crack density on the meso-texture of the material was found. The twin part of the meso-texture was described by the <111> rotation vectors of the TBs observed using the EBSD technique in the SEM. The rotation vectors of the damaged TBs were arranged in a "damaging cone" around the specimen axis. The risk of TB cracks in texturized rolling plates can be reduced by a favourable alignment of the specimen in the rolling plate avoiding the damaging cone of rotation vectors.

Tailoring the Properties of a Ni-Based Superalloy via Modification of the Forging Process: an ICME Approach to Fatigue Performance

“…Since the length of the persistent slip bands determine the likelihood of crack nucleation, populating the microstructure with a high density of Σ3 twin or high-CSL boundaries will serve to inhibit slip transmission across these boundaries and effectively limit their overall length [21]. Since the length of persistent slip bands are bounded by these Σ3 boundaries, the eventual nucleation of fatigue cracks will likely occur along these boundaries and is consistent with observations in both pure metals [22][23][24] and alloys [21,25,26]. Furthermore, the tendency of cracks to form along twin boundaries [26][27][28][29][30] can also be attributed to the high degree of elastic strain anisotropy [31,32] that exists across these boundaries and induce stress concentrations that lead to strain localization.…”

Effect of the Twins on Mechanical Properties of AISI 304 Stainless Steel Wire Using Electrical Current Method

“…Annealed twin boundaries with face-centered cubic lattice (FCC) demonstrated the lowest stacking fault energy. 13,14) Notably, the grain size of phase was about 34 mm and twin, martensite 15) and ferrite were in the matrix.…”

Cracking in a Fe–25Mn–3Si–3Al Steel

“…Previous studies show extensive evidences that twins could serve as favorable sites for the formation of fatigue cracks. [18,19] Twin boundary cracks were the dominating crack events at medium amplitudes in 316 austenitic stainless steels. [19,20] Finite element simulations also confirmed the substantial enhancement of the driving force for the crack formation in a twinned crystal relative to a single crystal.…”

“…[18,19] Twin boundary cracks were the dominating crack events at medium amplitudes in 316 austenitic stainless steels. [19,20] Finite element simulations also confirmed the substantial enhancement of the driving force for the crack formation in a twinned crystal relative to a single crystal. [21] Coherent twin boundaries in face centered cubic (FCC) metals are the ones with the lowest energy among all grain boundaries.…”