A continuum thermodynamics formulation for micromagnetics coupled with mechanics is devised to model the evolution of magnetic domain and martensite twin structures in ferromagnetic shape memory alloys. The theory falls into the class of phase-field or diffuseinterface modeling approaches. In addition to the standard mechanical and magnetic balance laws, two sets of micro-forces and their assoc...

We provide an extended Peierls–Nabarro (P–N) formulation with a sinusoidal series representation of generalized stacking fault energy (GSFE) to establish flow stress in a Ni2FeGa shape memory alloy. The resultant martensite structure in Ni2FeGa is L10 tetragonal. The atomistic simulations allowed determination of the GSFE landscapes for the (111) slip plane and 2 1⁄2 101 ; 2 1⁄2 110 ; 6 1⁄2 211...

Molecular dynamics simulations were performed to demonstrate the synergistic effects of the extrinsic size (nanowire length) and intrinsic size (twin boundary spacing) on the failure manner, yield strength, ductility and deformation mechanism of the twinned nanowires containing high density coherent twin boundaries CTBs paralleled to the nanowires’ axis. The twinned nanowires show an intense ex...

Lath martensite reveals a specific hierarchical subgrain structure, with laths, blocks and packets of particular crystallography. The presence of interlath retained austenite layers has been reported in the literature. This paper investigates the potential influence of the interlath retained austenite on the mechanical behaviour of lath martensite subgrains. To this purpose, a martensite grain ...

Ni39+x Mn50Sn11-x (x = 0.5, 1.0, 1.5 and 2) alloys comprise multiple martensite nanostrips of nanocrystallites when cast in small discs, for example, ∼15 mm diameter and 8 mm width. A single martensite phase with a L10 tetragonal crystal structure at room temperature can be formed at a critical Sn content of 9.0 at.% (x = 2), whereas an austenite cubic L21 phase turns up at smaller x ⩽ 1.5. The...

We study the behavior of crystals that undergo martensitic transformations. On cooling, the high-temperature phase (austenite) transforms to the martensite phase changing its crystalline symmetry. The lower crystalline symmetry of the martensite gives rise to several variants of martensite. Each variant has an associated transformation strain. These variants accommodate themselves (according to...

Shape-memory hacks were fabricated in a single processing step ("one-time procedure") by a combination of tensile and bending deformation of a martensitic NiTi-wire. The hacks reversibly changed curvature on heating and cooling in a reproducible manner over 50 thermal cycles. This new type of intrinsic two-way shape memory effect was studied by subjecting the hacks to a beam of high-energy sync...

Stimulated by recent experimental results on superelastic NiTi shape memory alloy, a theoretical study is carried out to quantify the effect of plasticity on stress-induced martensite transformation, using a constitutive model that combines phase transformation and plasticity. A constraint equation is introduced to quantify the phenomenon of the stabilisation of plasticity on stress-induced mar...

This work focuses on the stress-induced transformation in solutionized and overaged single-crystal NiTi alloys. The potential role of detwinning on the recoverable strains was investigated both theoretically and also with temperature-cycling experiments. The detwinning is the growth of one variant within a martensite in expense of the other. It is shown that the experimental recoverable strains...

The Au-Pd alloy has been proved to be an excellent catalyst in many applications, such as the electro-oxidation of formic acid, CO oxidation and oxidation of alcohols to aldehydes. However, most of the research has been focused on the shape-controlled Au-Pd alloy NCs with a single-crystal structure. Due to the existence of high-energy atoms on the twin defects, twinned structures usually will f...