Previous experiments have shown that stress-induced martensitic transformation in certain polycrystalline NiTi shape memory alloys can lead to strain localization and propagation phenomena when loaded in uniaxial tension. The number of nucleation events and kinetics of transformation fronts were found to be sensitive to the nature of the ambient media and imposed loading rate due to the release...

T his is the third paper in our series to identify unusual phenomena and to provide recommendations for the thermo-mechanical characterization of shape memory alloy (SMA) wire. Part 1 provided some basic background of the martensitic transformations responsible for the shape memory effect and superelasticity1. The characterization of two typical NiTi SMA alloys began with differential scanning ...

Sintered samples of monoclinic zirconia (α-ZrO2) have been irradiated at room temperature with 6.0-GeV Pb ions in the electronic slowing down regime. X-ray diffraction (XRD) and micro-Raman spectroscopy measurements showed unambiguously that a transition to the ‘metastable’ tetragonal phase (β-ZrO2) occurred at a fluence of 6.5x10 cm for a large electronic stopping power value (≈ 32.5 MeV μm). ...

The phase transition of crystalline ordering is a general phenomenon, but its evolution in space and time requires microscopic probes for visualization. Here we report direct imaging of the transformation of amorphous titanium dioxide nanofilm, from the liquid state, passing through the nucleation step and finally to the ordered crystal phase. Single-pulse transient diffraction profiles at diff...

The time-temperature transformation behavior of a rapidly solidified (RS) Ti-24Al-11Nb alloy has been studied between 450 and 850 “C using X-ray diffraction, electron diffraction, transmission electron microscopy and microindentation methods. A revised isothermal transformation path from the initial B2 to the final cz? structure has been proposed: B2 (Pmjm)B19 (Pmma)-0’ (Cmcm) 0’ (Cmcm) a2 (P6,...

Transformation thermodynamics, as one of the important branches among the extensions of transformation optics, has attracted plentiful attentions and interests recently. The result of transformation thermodynamics, or called as "thermal cloak", can realize isothermal region and hide objects from heat. In this paper, we presented the concept of "reverse thermal cloak" to correspond to the therma...

The non-isothermal transformation rate curves of metallic glasses are analyzed with the Master Curve method grounded in the Kolmogorov-Johnson-Mehl-Avrami theory. The method is applied to the study of two different metallic glasses determining the activation energy of the transformation and the experimental kinetic function that is analyzed using Avrami kinetics. The analysis of the crystalliza...

Effects of magnetic fields and hydrostatic presswes on the isothermal martensitic transformation, whose nose temperature is about 140% in an Fe-25.ONi-4.OCr alloy ( mass% ) has been examined by applying magnetic fields up to 30MA/m and hydrostatic presswes up to 1.SGPa The obtained results are the following: The martensitic transformation is induced instantaneously ( less than 20psec.) under pu...

  Abstract:   The aims of this research were to investigate the effects of semisolid metal (SSM) processing parameters (i.e., shear rates –times – temperatures combinations) on the primary solidification products and isothermal holding duration, subsequent to cessation of stirring on the secondary solidification of Al-Si (A356) alloy.   The dendrite fragmentation was found to be the governing m...