The compositional stability of the P-phase in Ni–Ti–Pd shape memory alloys

Coppa, Anne C.; Kapoor, Monica; Noebe, R.D.; Thompson, Gregory B.

doi:10.1016/j.intermet.2015.07.014

Cited by 8 publications

(2 citation statements)

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“…From the selected area diffraction (Figure 5c), the precipitates were identified to be the P phase [44,45]. The formation of the P phase in the 49Ti alloys is reasonable because the composition of the P phase is reported to be slightly Ti-poor, such as Ti 11 (Ni 7 Pd 6 ) [46]. These results imply that the change of the transformation temperatures during thermal cycling in the alloys with off-stoichiometric composition is due to the formation of precipitates.…”

Section: Resultsmentioning

confidence: 99%

Effect of Stoichiometry on Shape Memory Properties and Functional Stability of Ti–Ni–Pd Alloys

et al. 2019

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Ti–Ni–Pd shape memory alloys are promising candidates for high-temperature actuators operating at above 373 K. One of the key issues in developing high-temperature shape memory alloys is the degradation of shape memory properties and dimensional stabilities because plastic deformation becomes more pronounced at higher working temperature ranges. In this study, the effect of the Ti:(Ni + Pd) atomic ratio in TixNi70−xPd30 alloys with Ti content in the range from 49 at.% to 52 at.% on the martensitic transformation temperatures, microstructures and shape memory properties during thermal cycling under constant stresses were investigated. The martensitic transformation temperatures decreased with increasing or decreasing Ti content from the stoichiometric composition. In both Ti-rich and Ti-lean alloys, the transformation temperatures decreased during thermal cycling and the degree of decrease in the transformation temperatures became more pronounced as the composition of the alloy departed from the stoichiometric composition. Ti2Pd and P phases were formed during thermal cycling in Ti-rich and Ti-lean alloys, respectively. Both Ti-rich and Ti-lean alloys exhibited superior dimensional stabilities and excellent shape memory properties with higher recovery ratio and larger work output during thermal cycling under constant stresses when compared with the alloys with near-stoichiometric composition.

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Section: Resultsmentioning

confidence: 99%

Effect of Stoichiometry on Shape Memory Properties and Functional Stability of Ti–Ni–Pd Alloys

et al. 2019

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“…To meet demands of different applications, their martensitic transformation characteristics and thermomechanical properties often need to be altered and controlled. One commonly used method to alter and control the properties is to add a third element into the binary NiTi, such as Cu, Nb, Hf and Pd [15][16][17][18][19]. Among them, Cu substitution for Ni is known to introduce an intermediate orthorhombic B19 phase in its martensitic transformation sequence, to narrow the transformation hysteresis [20], and to enhance thermal and mechanical cycling stability [21,22].…”

Section: Introductionmentioning

confidence: 99%

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

Bakhtiari

Liu

et al. 2019

Acta Materialia

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Ti50Ni50-xCux alloys are observed to exhibit multiple martensitic transformations from B2 to an orthorhombic B19 and a monoclinic B19′ phase. In addition, DFT calculations have predicted a B19ʺ phase with a higher monoclinic angle as the thermodynamically stable ground state. This study investigated the effects of Cu content and shear stress on the monoclinic angles, phase stabilities of the various martensites, the minimum energy pathways, and the relative total energies among the phases in this pseudo-equiatomic Ti(Ni50-xCux) system. A new monoclinic phase (B19M) with a monoclinic angle lower than that of B19′ was found at above a critical Cu content. This confirms the formation of an intermediate phase in the martensitic transformation sequence of the pseudo-equiatomic Ti(Ni50-xCux) system but contradicts the crystal structure of the experimentally observed phase. It was found that the monoclinic angles of both B19M and B19ʺ decrease with increasing the magnitude of an opposing shear stress to their monoclinic distortion. At above certain critical values of the opposing shear stress, the B19M and B19ʺ phases destabilise and transform to lower monoclinic angle phases. In addition, the evidence suggests that the experimentally observed monoclinic B19′ phase is in fact a distorted B19ʺ with a reduced monoclinic angle under an opposing shear stress. With the same argument, the experimentally reported B19 phase is a metastable phase formed under the effect of an opposing shear stress to the monoclinic distortion of B19M.

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