First‐principles study on the elastic properties and electronic structure of TiNi‐based ternary shape memory alloys

Abstract

TiNi-based shape memory alloys have been widely used in the fields of engineering and medicine due to their shape memory effect and superelasticity, which are displayed during martensitic transformations [1]. However, the martensitic transformation in this system is least understood compared with other systems due to the complexity of the transformation and sensitivity to alloying addition. It is well known that most TiNi-based alloys have an ordered B2 phase at high temperatures and transform to a stable low temperature martensitic phase when the temperature decreases. For TiNi alloy, the parent B2 phase transforms into a monoclinic B19′ martensite. Moreover, the martensitic transformation of TiNi alloy is significantly affected by the addition of the third elements as regards the transformation temperature [2][3][4]. With Fe addition, the martensitic transformation temperature is decreased drastically [5]. With low addition of Pd and Cu, the martensitic transformation temperatures are also decreased [6]. Despite the importance of these transformations in applications of TiNi-based alloys, several fundamental aspects of these transformations have not been well understood. The most puzzling problem is the origin of the unique B19′ martensite, which found no analogy in other usual B2 alloys, such as CuZn and NiAl. The second puzzle is the mechanism of the effect of the third element on the martensitic transformation temperature of TiNi. Some previous works show that the martensitic transformation is related both to elastic properties and electronic structure [7][8][9][10]. Recently, Ren and Otsuka et al. [11] proposed that the B19′ martensite structure is a result of the coupling between a non-basalplane shear (the C 44 shear) and the basal plane shear (the C′ shear), and verified this argument by some experimental studies of elastic constants of TiNi-based alloys. But studies on the origin of the B19′ martensite from theoretical calculation of their elastic properties have not been reported, and the second puzzle has still remained unclear.In this paper, we report the first theoretical results on the elastic properties and electronic structure of B2 shape memory alloys by the first-principles method for understanding their martensitic transformation behavior. The calculations presented in this study are performed with the CASTEP code [12], based on density functional theory, using Vanderbilt-type ultrasoft pseudopotentials [13] and a plane-wave expansion of the wave functions. We use the local density approximation (LDA) to describe the exchange and correlation potential. The structure is optimized with the Broyden-Fletcher-Goldfarb-Shanno (BFGS) method, and convergence is assumed when the forces on atoms are less than 0.03 eV/Å. The plane-wave cutoff energy of 550 eV is employed. The calculations are done using a (14, 14, 14) Monkhorst-Pack grid. As for shape memory alloys are studied by the plane-wave psedudopotential method within the local density approximation. The elastic constants and density of states are...

First-principles study on alloying effect on martensitic transformation behavior of TiNi alloy

“…Very recently, we experimentally found that low addition of Ce in TiNi increases the martensitic transformation tem- 6.25 have been calculated in our previous work [17]. The results show that the shapes of all total DOS curves are similar and all of them comprise two sets of peaks separated by a dip.…”

“…Higher stability corresponds to lower total DOS value at the Fermi level. In addition, our previous work [17] shows that the total DOS at the Fermi level is primarily offered by the Ti d DOS. Thus we conclude that higher stability corresponds to lower Ti d DOS value at the Fermi level.…”

“…In every case, the geometrical optimization is always made, based upon which the elastic constants and electronic structure are then calculated. In our previous work [17], we have calculated the elastic constants and electronic structure of Ti 50 Ni 43.75 Fe 6.25 , Ti 50 Ni 43.75 Pd 6.25 and Ti 50 Ni 43.75 Cu 6.25 . In this paper, we discuss them and the others together.…”

Effect of Ternary Additions X (Co, Rh, Ir) on Electronic Properties of TiPd Shape Memory Alloy: An ab-initio Study

“…It is known that the stability of Ti-based B2 phase compounds are determined by the Ti d-states at Fermi level. In Ti-based compounds, higher stability corresponds to a lower Ti d DOS value at the Fermi level [18]. The higher stability of Ti 43.75 Pd 50 X 6.25 can be attributed to the decrease in the density of d states of Ti and X at Fermi level with increasing atomic number of X impurities.…”

Study of shape memory properties of Ti(50)Ni(50-x) Mx (M= Nb, Mo and Fe) alloys for biomedical applications using first principle approach

“…At high temperatures, TiNi-based alloys possess an ordered B2 austenitic phase that transforms to a stable lower-temperature martensitic phase as the temperature drops. The parent B2 phase changes into a monoclinic B19′ martensite in TiNi alloy [3]. The high-temperature state is frequently a 𝛼𝛼-phase with a body-centred cubic (bcc) structure, whereas the lower temperature phase has a hexagonal close packed 𝛽𝛽 martensitic structure, given this, a metallic composition which will exist in the primitive 𝛽𝛽 -phase at ambient temperatures must be chosen [4].…”