Effect of Hydrogen on the Properties of Rapidly Quenched Tini-Ticu Alloys with Shape Memory
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EFFECT OF HYDROGEN ON THE PROPERTIES OF RAPIDLY QUENCHED TiNi – TiCu ALLOYS WITH SHAPE MEMORY N. E. Skryabina,1 L. V. Spivak,1 D. Fruchart,2 and A. V. Shelyakov 3
UDC 669.295.24: 669.788
We show that, after the introduction of hydrogen into rapidly quenched Ti50 Ni25 Cu25 alloys in the crystalline, amorphous, or amorphous-crystalline state, their shear modulus and electric resistance change appreciably. Subsequent thermocycling of these alloys is evidence of the suppression of direct and inverse martensitic transformations B2 ↔ B19 (B19′ ) due to hydrogen.
The influence of electrolytically introduced hydrogen on the phase composition and the temperatures T R of B2 → R phase transition (PT) and Ms of R → B19′ (B2 → B19′ ) PT was studied earlier [1 – 3] on foils of three alloys based on TiNi with different temperatures of B2 → R and R → B19′ phase transitions. It turned out that the saturation of TiNi alloys with hydrogen from an electrolyte affects ambiguously the temperature Ms and practically does not change the temperature TR . In all cases, B2 → R, B2 → B19′, and R → B19′ PT become more active [2, 3]. The products of these transformations (B19′ martensite and the R-phase) are oriented with respect to the surface of the foil. The hydride phase was not found. The action of hydrogen on PT is usually connected with its influence on the instability of the crystal lattice of the B2-phase, and the formation of oriented martensite and the R-phase is explained by the anisotropic hydrogen distribution in the martensite lattice and surface phenomena in the course of hydrogen saturation of thin foils. The induced transformations are a result of the stresses created by hydrogen in the crystal lattice of the B2-phase. Such stresses relax in these transformations and cannot be detected by radiographic analysis. In [4, 5], the behavior of foils of TiNi alloys with different initial structural states (B2, B2 + B19′, and R + B19′ ) was considered for the case of hydrogen saturation and subsequent heating. In the alloy with initial structure B2 at – 40°C, B2 → R transition is observed without B2 → B19′ transformation up to – 196°C. Therefore, according to [4, 5], martensite arising in the course of saturation of the alloy with hydrogen is purely “hydrogenous” with the preferential orientation [111]. As established in [6], the introduction of hydrogen at 300 K into the crystal lattice of “nitinol” alloys (a wire of diameter 0.5 mm) with different temperatures of the beginning of PT activates creep flow, leads to dilatation, and increases the electric resistance and shear modulus. The saturation of a TiNi alloy with hydrogen initiates B2 → R transition. The discovered effects of plasticity of this transformation and shape memory differ in principle, as to their physical nature, from the well-known deformation effects in TiNi alloys. An increase in the phase transition points in hydrogenated “nitinol” alloys at their heating and cooling from the β-state was not established. On the contrary, a tendency to a certain decrease in thes
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