Self accomodating shear strain

The lattice-variant transformation dislocations originate from the three-dimensional network, where screw dislocation segments dissociate to form fluctuating microdomains (localized soft modes), and these thicken when the transformation dislocations multiply by a cross-slip dissociation mechanism.The computed Schmid factors for variants in self-accommodating groups show opposite signs, indicative of a minimum long-range stress field.The resulting low energy dislocation structure is an interface of primary shear dislocations of alternating signs and habit plane shear dislocations in self-accomodating variants with almost opposite shear strains.The results indicate criteria for high pseudoelasticity and shape memory behavior with a mobile low energy dislocation structure which is highly susceptible to an applied stress.Two main contradictory arguments exist concerning the deformation mechanisms of those alloys, i.e., formation of reversible nanodisturbance and reversible martensitic transformation.Herein we used the in-situ synchrotron high-energy X-ray scattering technique to reveal the novel intrinsic physical origin of all anomalous mechanical properties of the Ti-24Nb-4Zr-8Sn-0.10O alloy, a typical gum-like metal.The martensitic microstructure of shape memory alloy (SMA) is essentially an aggregate of martensite plate groups.

The dependence of the measured heat on the mart-ensite fraction transformed in the partial cycles is achieved and analyzed.

The low energy dislocation structures in microdomains, twin domains and self-accommodating interfaces, causes by martensitic transformations, are evaluated for several B2 alloys with 18R, 9R and 3R martensite structures by the modern theory of martensitic transformations.

The transformations are accomplished by two lattice-variant shears and a volume change relaxation and are one dimensional in origin when the order parameter couples linearly with the spontaneous strain.

The aim of the present study is two-fold: (1) to estimate the deviatoric and the hydrostatic components of the total transformation strain in different possible self-accommodating clusters, and, (2) to experimentally determine the nature of self-accommodation in Ni-Ti SMA from the effect of the unaccommodated strain field on the transformation temperatures.

ABSTRACT: The hysteresis loop interior of thermoelastic martensitic transformations of Ti Ni-base shape memory alloys including the transformation with invariant plane is investigated in the partial transformation cycles and discussed.

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