The nucleation of bcc austenite in a single crystal of a mechanically stabilized 2H-martensite of Cu-Al-Ni shape-memory alloy is studied. The nucleation process is induced by localized heating and observed by optical microscopy. It is observed that nucleation occurs after a time delay and that the nucleation points are always located at one of the corners of the sample (a rectangular bar in the...

Abstract: The properties of SMA (Shape Memory Alloys, that are smart materials) are associated to a first order phase transition named martensitic transformation that occurs between metastable phases: austenite and martensite. At upper temperature or at lower stress the austenite is the metastable phase. The martensite appears at lower temperature or higher stresses. The hysteresis of the trans...

This article presents a study of fatigue-crack propagation behavior in Nitinol, a 50Ni-50Ti (at. pct) superelastic/shape-memory alloy, with particular emphasis on the effect of the stress-induced martensitic transformation on crack-growth resistance. Specifically, fatigue-crack growth was characterized in stable austenite (at 120 8C), superelastic austenite (at 37 8C), and martensite (at 265 8C...

Ni1 2 Mn Ga ( 0 2 and 0.25) alloys in thin film form were prepared by ion-beam sputtering from alloy targets. For Si(001) substrates the structure/texture of the films are a function of the growth temperature ( ). The tetragonal martensite structure with a (220) texture was obtained for an optimal 300–350 C. At higher temperatures a cubic silicide (Mn12Ni4Si3) was obtained. At room temperature,...

The electronic structure and magnetism of the Heusler alloy Mn2NiAl have been studied by firstprinciples calculations. It is found that the phase transformation from the cubic to the tetragonal structure lowers the total energy, indicating that the martensitic phase is more stable and that a phase transition from austenite to martensite may happen at a lower temperature. Thus, ferromagnetic sha...

Many models simulating the behavior of Shape Memory Alloys (SMA) exist nowadays, in the one or three dimensional situation. In most of the cases they are not able to describe the non isothermal behavior of SMA due to the thermomechanical loadings. Indeed, the influence of the stress on the product phase leads to an orientation of the variants, when the temperature creates a self-accomodating ma...

This paper proposes a method to calculate the uniaxial stress /strain relationship of polycrystalline Fe /Pd, which has a martensite structure produced by cooling. Strain is caused by changes in the fractions of the three Bain corresponding variants which form the martensite structure within each grain. Internal stress and elastic energy are accumulated as straining proceeds and are caused by d...

A phase-field theory of transformations between martensitic variants and multiple twinning within martensitic variants is developed for large strains and lattice rotations. It resolves numerous existing problems. The model, which involves just one order parameter for the description of each variant-variant transformation and multiple twinnings within each martensitic variant, allows one to pres...

We present here results of temperature dependent high resolution synchrotron x-ray powder diffraction study of sequence of phase transitions in Ni2MnGa. Our results show that the incommensurate martensite phase results from the incommensurate premartensite phase, and not from the austenite phase assumed in the adaptive phase model. The premartensite transforms to the martensite phase through a ...

We report results on a nite element simulation of a needle-like martensitic microstructure observed in biaxial loading experiments conducted by Chu and James on single crystals of the shape-memory alloy Cu-14at.%Al-3:9at.%Ni. This microstructure was observed near an interface between twinned layers of two variants and a pure variant of martensite. We used a geometrically nonlinear theory of mar...