TY - JOUR

T1 - Origin of the isothermal B2 → B19′ transformation in NiTi-based shape memory alloys

AU - Belyaev, Sergey

AU - Resnina, Natalia

AU - Demidova, Elena

AU - Ivanov, Alexey

AU - Shelyakov, Alexander

AU - Andreev, Vladimir

AU - Chekanov, Valeriy

AU - Ubyivovk, Evgenii

N1 - Publisher Copyright: © 2022 Elsevier B.V.

PY - 2022/5/5

Y1 - 2022/5/5

N2 - The aim of this paper was to study the isothermal forward martensitic transformation in binary, ternary, and quaternary NiTi-based shape memory alloys to find the origin of this phenomenon. The results obtained showed that the isothermal B2 → B19′ transformation was observed only in the NiTi-based alloys with substitutional defects. The critical concentration of copper was found that completely suppressed the martensitic transformation both on cooling or isothermal holding in Ti-Hf-Ni-Cu alloys. The thermodynamics of the martensitic transformation that occurred in the presence or absence of the substitutional defects was discussed, and the reason for the influence of the substitutional defects on the martensitic transformation was clarified. It was verified that the formation of the martensite phase on isothermal holding was caused by the local fluctuation of the substitutional defect concentration which led to fulfilment of the thermodynamic condition for the martensitic transformation. It was shown that the maximum volume fraction of the isothermal martensite was limited by the maximum volume of martensite that corresponded to the thermal elastic equilibrium and appeared on cooling of the alloy without substitutional defects. The results allowed to conclude that the martensitic transformation remained to be thermal elastic in the NiTi-based alloys with a non-stoichiometric composition however, the martensite nucleation was controlled by the thermally activated migration of substitutional defects.

AB - The aim of this paper was to study the isothermal forward martensitic transformation in binary, ternary, and quaternary NiTi-based shape memory alloys to find the origin of this phenomenon. The results obtained showed that the isothermal B2 → B19′ transformation was observed only in the NiTi-based alloys with substitutional defects. The critical concentration of copper was found that completely suppressed the martensitic transformation both on cooling or isothermal holding in Ti-Hf-Ni-Cu alloys. The thermodynamics of the martensitic transformation that occurred in the presence or absence of the substitutional defects was discussed, and the reason for the influence of the substitutional defects on the martensitic transformation was clarified. It was verified that the formation of the martensite phase on isothermal holding was caused by the local fluctuation of the substitutional defect concentration which led to fulfilment of the thermodynamic condition for the martensitic transformation. It was shown that the maximum volume fraction of the isothermal martensite was limited by the maximum volume of martensite that corresponded to the thermal elastic equilibrium and appeared on cooling of the alloy without substitutional defects. The results allowed to conclude that the martensitic transformation remained to be thermal elastic in the NiTi-based alloys with a non-stoichiometric composition however, the martensite nucleation was controlled by the thermally activated migration of substitutional defects.

KW - Isothermal transformation

KW - Kinetics

KW - Martensitic transformation

KW - NiTi

KW - Thermodynamics

KW - THERMODYNAMIC ANALYSIS

KW - KINETICS

KW - THERMOELASTIC MARTENSITIC TRANSFORMATIONS

UR - http://www.scopus.com/inward/record.url?scp=85122696675&partnerID=8YFLogxK

U2 - 10.1016/j.jallcom.2021.163570

DO - 10.1016/j.jallcom.2021.163570

M3 - Article

AN - SCOPUS:85122696675

VL - 902

JO - Journal of Alloys and Compounds

JF - Journal of Alloys and Compounds

SN - 0925-8388

M1 - 163570

ER -