Influence of current density upon hydrogenation on the shape memory effect of binary TiNi alloy single crystals

doi:10.3390/met13081412

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DOI Доступ к ресурсу на сайте издателя			10.3390/met13081412

Title: Influence of current density upon hydrogenation on the shape memory effect of binary TiNi alloy single crystals
Creator: Kireeva, Irina V. (физик)
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Chumlyakov, Yuri I.
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Yakovleva, Liya P.
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Vyrodova, Anna V.
Date: 2023
DOI: 10.3390/met13081412
Description: Some results concerning the hydrogen effect at electrolytic saturation at a current density of j = 1500 and 3500 A/m2 for 3 h at room temperature on the temperature dependence of the yield stress 0.1(T) and the shape memory effect (SME) under tension of the [011]-oriented Ti-50.55%Ni (at.%) alloy single crystals are presented. It was shown that hydrogen is in a solid solution and forms particles of titanium hydride TiH2 after hydrogenation at j = 1500 and 3500 A/m2, respectively. Both hydrogen in the solid solution and TiH2 particles led to a decrease in the Ms temperature of the onset of the forward martensitic transformation (MT) upon cooling and the Md temperature (Md is the temperature at which the stresses for the onset of the stress-induced MT are equal to the stresses for the onset of plastic flow of the high-temperature B2 phase), and increased the yield stress 0.1 of the B2 phase at the Md temperature compared to hydrogen-free crystals. It was found that the SME under stress depends on the tensile stress level and current density. The maximum SME "SME = 10 0.2% at ex = 200 MPa and "SME = 10.5 0.2% at ex = 300 MPa was observed in the hydrogen-free crystals and after hydrogenation at j = 1500 A/m2, respectively, which exceeded the theoretical value of lattice deformation "0 = 8.95% for the B2-B190 MT in [011] orientation under tension. At j = 1500 A/m2, the physical reason for the excess of the SME of the theoretical "0 value was due to the increase in the plasticity of B190 martensite upon hydrogenation. At j = 3500 A/m2, "SME = 8.0 0.2%, and it was less than "0 = 8.95% for B2-B190 MT in [011] orientation under tension. The decrease in SME after hydrogenation at j = 3500 A/m2 was associated with the interaction of two types of B190-martensite: oriented under stress and non-oriented, formed near TiH2 particles. It was shown that the redistribution of hydrogen in the bulk of the crystals during long-term holding for 168 h at 263 K after hydrogenation at j = 1500 A/m2 increases the SME relative to crystals without long-term holding: 3.5 times at 50 MPa and 1.8 times at 100–150 MPa. After long-term holding, "SME = 9.5 0.2% at 150 MPa, which exceeds the theoretical value "0 = 8.95% for B2-B190 MT in [011] orientation under tension.