Shape memory behavior in Fe₃Al-modeling and experiments

Abstract

The Fe 3 Al alloy with D0 3 structure exhibits large recoverable strains due to reversible slips. Tension and compression experiments were conducted on single crystals of Fe 3 Al, and the onset of slip in forward and reverse directions were obtained utilizing high-resolution digital image correlation technique. The back stress provides the driving force for reversal of deformation upon unloading, resulting in a superelastic phenomenon as in shape memory alloys. Using density functional theory simulations, we obtain the energy barriers (GSFE -generalized stacking fault energy) for {1 1 0}〈1 1 1〉 and {1 1 2} 〈1 1 1〉 slips in D0 3 Fe 3 Al and the elastic moduli tensor, and undertake anisotropic continuum calculations to obtain the back stress and the frictional stress responsible for reversible slip. We compare the theoretically obtained slip stress magnitudes (friction and back stress) with the experimental measurements disclosing excellent agreement.

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

“…Recently, the present authors reported the CRSS values attained by the first principle, Density Functional Theory (DFT) calculations on DO 3 -Fe 3 Al. Fig.1(a), adopted from this aforementioned study, illustrates the asymmetry in <111> cross sections of  curves on planes exhibiting the break-down of Schmid Law [21]. This asymmetry is also reflected on the resolved shear stress vs shear strain curves in Fig.1(b).…”

“…A stress concentrator was inserted inside the pristine crystal of DO 3 -Fe 3 Al as a straight dislocation source. In 8 order to evaluate the theoretical CRSS values on the glide plane, we utilized the modified P-N formalism [21]. This formalism relates Peierls stress to the gradient of the total energy of the system with respect to the position of the dislocation line.…”

“…The term  represents the GSFE landscape of the system on either {1 1 0} or {1 1 2} slip planes along the slip direction and is written as a function of the atomistic disregistry function, () fx, which is also a function of x coordinate on the glide plane perpendicular to the dislocation lines [21,41]. The  values are attained by utilizing the control box method [42,43].…”

“…Thus, the nature of the underlying mechanisms are more complicated because of the mutual interactions. As stated earlier, our main focus in this study be will be the non-Schmid plastic behavior of DO 3 -Fe 3 Al which is an intermetallic exhibiting superelastic behavior due to reversible slip [21][22][23][24][25]. In DO 3 structured metallic materials, plastic strain is accommodated by the glide of <111> superdislocations which are dissociated into four 1/4 <111> superpartials.…”

“…The onset of slip in single crystals was identified precisely using high resolution, in-situ DIC strain measurements. Concurrently, MD simulations were utilized to evaluate the theoretical CRSS values by the modified P-N formalism [21]. The close agreement of both approaches on the non-Schmid response of DO 3 -Fe 3 Al, stimulated further interrogation on the role of the core structure.…”