We present models of the microstructure of martensite that occurs when twinned layers of martensite meet a pure variant. This microstructure often occurs below the A, temperature, with loading that favors the passage from one pure variant of martensite to another. This microstructure gives a mechanism for variant rearrangement. In this microstructure, the layers are observed to pinch down to sh...

We have constructed a complete hydrodynamic theory of nucleation and growth in a one–dimensional version of an elastic shear martensitic transformation with open boundary conditions where we have accounted for interfacial energies with strain–gradient contributions. We have studied the critical martensitic nuclei for this problem: Interestingly, the bulk critical nuclei are twinned structures, ...

Ni2FeGa is a relatively new shape memory alloy (SMA) and exhibits superior characteristics compared to other SMAs. Its favorable properties include low transformation stress, high reversible strains and small hysteresis. The first stage of stress-induced martensitic transformation is from a cubic to a modulated monoclinic phase. The energy barriers associated with the transformation from L21 (c...

Abstract In the present research, the behavior of 304L austenitic stainless steel in the deep drawing process has been studied at the room temperature through experimental and finite element simulation method. Magnetic method calibrated by XRD was used to measure induced-martensite. Martensite volume fraction in the various portion of the deep drawn cup under optimum Blank Holder Force (BHF) a...

The classification of martensitic displacive transformations into athermal, isothermal or anisothermal is discussed. Athermal does not mean “no temperature dependence” as is often thought, but is best considered to be short for the notion of no thermal activation. Processes with no thermal activation do not depend on time, as there is no need to wait for sufficient statistical fluctuations in s...

A constitutive model to describe macroscopic elastic and transformation behaviors of polycrystalline shape-memory alloys is formulated using an internal variable thermodynamic framework. In a departure from prior phenomenological models, the proposed model treats initiation, growth kinetics, and saturation of transformation distinctly, consistent with physics revealed by recent multi-scale expe...

The investigations till now performed on the Step-wise Martensite to Austenite Reversible Transformation (SMART) have identified the relevant key features both of the transformation itself and of the Incomplete Cycling on Heating (ICH), procedure required to induce the SMART. The SMART phenomenology, proved in several shape memory alloys, appears quite general, despite of the differences both i...

Nano-structured NiTi instantaneously transforms from fcc austenite via an intermediate phase (the R-phase) into monoclinic B19’ martensite. At a grain size less than a critical limit of about 50nm no transformation can be observed even upon cooling down to cryogenic temperatures. In slightly larger grains the martensite appears as a laminate of alternating twinrelated Bain correspondence varian...

Shape memory alloys are typical temperature-sensitive metallic functional materials due to superelasticity and shape recovery characteristics. The conventional shape memory effect involves the formation and deformation of thermally induced martensite and its reverse transformation. The shape recovery process usually takes place over a temperature range, showing relatively low temperature-sensit...