Monoclinic angle, shear response, and minimum energy pathways of NiTiCu martensite phases from ab initio calculations

Bakhtiari, Sam; Liu, Jefferson Zhe; Liu, Yinong; Yang, Hong

doi:10.1016/j.actamat.2019.07.050

Cited by 4 publications

(2 citation statements)

References 39 publications

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“…In these analyses B19″ was absent (not mentioned). In our recent work using ab initio calculation to analyse the phase stabilities in NiTi [24], we found that the B19′ phase is in fact a mechanically distorted state of B19″ instead of a phase in its own right with a local energy minimum. In this regard, the effect of an opposing shear stress may be described as to destabilise the BCO phase relative to B19″ and at the same time to reduce the monoclinic angle of B19″ to that of the observed B19′ phase.…”

Section: Introductionmentioning

confidence: 97%

Ab initio prediction of phase stability of martensitic structures in binary NiTi under hydrostatic tension

Bakhtiari¹,

Liu

Shariat³

et al. 2020

Phys. Scr.

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Near-equiatomic NiTi is known to exhibit multiple martensitic allotropes, including B19′, B19″ and base-centred orthorhombic (BCO). Formation of these martensites is associated with volume expansions, thus hydrostatic loading has direct influence on the stability, ground-state, transformation pathways and the structures of these phases. This work was conducted to clarify some uncertainties in the literature concerning the effect of hydrostatic tension on these properties of the martensite allotropes using the generalised solid-state nudge elastic band method implemented in density functional theory. It was found that higher hydrostatic compression favours phases of lower specific volumes, and higher hydrostatic tension favours phases of higher specific volumes. B19′ is stable at above 2 GPa compression, B19″ is stable within −6 GPa tension and 6.6 GPa compression and BCO is stable between −8 GPa tension and 8.8 GPa compression.

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Section: Introductionmentioning

confidence: 97%

Ab initio prediction of phase stability of martensitic structures in binary NiTi under hydrostatic tension

Bakhtiari¹,

Liu

Shariat³

et al. 2020

Phys. Scr.

Self Cite

View full text Add to dashboard Cite

show abstract

“…In recent scientific literature, interest was devoted to nano-structuration by ball milling and to preparation by sintering processes from powders [ 19 , 20 , 21 , 22 ]. Moreover, several studies involve theoretical calculations and simulations to correlate the macroscopic and functional properties of NiTi alloys to microstructural characteristics and to explore the martensitic path and evolution [ 23 , 24 , 25 , 26 ]. Concerning the damping properties, the grain size, martensite interface density, and defect structure are important internal variables and, in the case of NiTiCu, the Cu addition enhances the behavior of the NiTi system [ 5 , 27 ].…”

Section: Introductionmentioning

confidence: 99%

Microstructural and Thermo-Mechanical Characterization of Cast NiTiCu20 Shape Memory Alloy

et al. 2021

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Among NiTi-based alloys, one of the most promising and exploited alloys is NiTiCu, since the addition of Cu in substitution of Ni in the binary equiatomic NiTi has a significant influence on the martensitic transformation and the thermomechanical properties of the system. A high content of Cu improves the damping properties at the expense of phase homogeneity and workability. The present study focuses on an alloy with a high copper content, i.e., 20 at.%. For this specific composition, the correlation between the thermal treatments, microstructure, formation of secondary phases, and damping properties are investigated by several analyses. The microscopic observation, together with the compositional analysis, allowed the determination of four different phases in the alloy. Both the calorimetry and dynamic thermo mechanical measurements, which confirmed the high damping ability of the alloy, provided a characterization of the martensitic transition. Finally, the electron backscatter diffraction (EBSD) analysis detected the different crystallographic structures (i.e., cubic austenite, orthorhombic martensite, and cubic (face-centered) NiTi2) and their orientation in the different phases. Therefore, the present work aims to improve the knowledge of the role of secondary phases in the optimization of the NiTiCu20 alloy as a valuable alternative to typical alloys used for damping purposes.

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Effects of Point Defects on the Monoclinic Angle of the B19″ Phase in NiTi-Based Shape Memory Alloys

Li,

Bakhtiari,

Yang

et al. 2023

Shap. Mem. Superelasticity

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This study investigated the effects of a variety of point defects on the monoclinic angle of the B19″ martensite in NiTi, including Ni and Ti vacancies, Ni–Ti anti-sites in the lattice, third element substitution, and Ni and Ti enrichments in the B2 stoichiometry. Their effects were studied by density functional theory calculations on the monoclinic B19″ phase as a proxy for the experimentally observed B19′ phase. It was found that vacancies and Ni–Ti anti-sites reduce the monoclinic angle of B19″, whereas third element substitution of Ni and Ti may affect the monoclinic angle in both directions depending on the third element and the host element it replaces. Enriching Ni or Ti content to deviate from the B2 stoichiometry decreases the monoclinic angle. A change in the monoclinic angle of the B19″ phase implies variation in the characteristic strains associated with the transformation. Thus, these findings may provide a new angle on possible interpretations of the variations of recoverable transformation strains experimentally observed of NiTi shape memory alloys.

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Monoclinic angle, shear response, and minimum energy pathways of NiTiCu martensite phases from ab initio calculations

Cited by 4 publications

References 39 publications

Ab initio prediction of phase stability of martensitic structures in binary NiTi under hydrostatic tension

Ab initio prediction of phase stability of martensitic structures in binary NiTi under hydrostatic tension

Microstructural and Thermo-Mechanical Characterization of Cast NiTiCu20 Shape Memory Alloy

Effects of Point Defects on the Monoclinic Angle of the B19″ Phase in NiTi-Based Shape Memory Alloys

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