Non-Schmid response of Fe3Al: The twin-antitwin slip asymmetry and non-glide shear stress effects

Abstract

The non-Schmid effects in DO 3 ordered Fe 3 Al (DO 3-Fe 3 Al) are investigated by utilizing experimental measurements of the onset of slip and atomistic scale simulations to study slip directionality and core effects. Uniaxial tension and compression experiments were conducted on DO 3-Fe 3 Al single crystals utilizing high resolution Digital Image Correlation (DIC) to measure local slip strain evolution. The measured critical resolved shear stress (CRSS) values exhibited close agreement with the theoretical values upon developing a modified Peierls-Nabarro (P-N) formalism relying on molecular dynamics (MD) simulation results. Both experimental and theoretical values indicate the breakdown of Schmid Law due to two factors: the role of non-glide shear stress, called the NGS effect, component on the glide plane, and twinning-antitwinning asymmetry, termed the TA effect. To ascertain the role of NGS component on the dislocation core structures, molecular statics (MS) simulations were conducted upon imposing elasticanisotropic dislocation displacement fields with Eshelby-Stroh formalism. Both experimental measurements and modified P-N calculations confirm that the applied NGS component is as important as TA slip asymmetry on the breakdown of Schmid Law in CRSS values. The calculated core spreading suggests that the extent of the relative displacements on {1 1 0} family planes, favoring either twinning or antitwinning shear, can significantly contribute to the non-Schmid behavior of DO 3-Fe 3 Al with the accompanying elastic shear coupling between NGS component and glide shear (GS)

Non-glide effects and dislocation core fields in BCC metals

“…Used with a computationally efficient energy model which allows to model long three-dimensional dislocations, the core eigenstrain variation during kink-pair nucleation can also be computed directly and incorporated in a dislocation mobility law. 47,48 We note finally that the present approach is not limited to pure BCC metals and can be applied to other systems, which show nonglide effects, such as ordered BCC alloys, as NiTi 49 or Fe 3 Al 50 and hexagonal metals, 51,52 including twinning. 53…”

Relationship Between Functional Fatigue and Structural Fatigue of Iron-Based Shape Memory Alloy FeMnNiAl

“…2 imply a strong non-Schmid response of transformation stress, i.e., the CRSS for transformation is 190 MPa for h001i and 280 MPa for h013i (in both the cases the Schmid Factor for the activated variant was 0.48). Non-Schmid response has been observed in Fe 3 Al [59,60], NiTi [61] and CuZnAl [62] but not well studied for other SMAs. However, under a given external stress magnitude, this orientation dependence and dissimilar transformation stress levels can clearly induce transformation strain magnitudes at the notch that are far higher in the h001i case compared to h013i orientation.…”

Crystal plasticity modeling of non-Schmid yield behavior: from Ni3Al single crystals to Ni-based superalloys

“…The γ′ phase, with L12 crystal structure, exhibits asymmetric, orientation-and temperature-dependent yield behavior in tension and compression. This type of anomalous behavior is also exhibited by various alloy forms with the L12 crystal structure, like Ni3Ga Kuramoto, 1973, 1971), Ni3Ge (Pak et al, 1977), Ni3Si (Thornton et al, 1970) and Fe3Al (Alkan and Sehitoglu, 2017a) and also B2 type NiTi crystals (Alkan and Sehitoglu, 2017b). One of the reasons contributing to this observed effect is the deviation from the widely accepted Schmid law (Schmid and Boas, 1950) for crystalline metals.…”