Formation of vacancy-type defects in titanium nickelide

Abstract

Abstract. In this report we briefly review the current state-of-the-art and challenges in determining point defect properties from first-principles calculations as well as from experimental measurements in titanium nickelid. Based on the vacancy formation energy and the activation energy for vacancy migration in TiNi, vacancy mediated diffusion mechanism was examined. The influence of vacancies and antisite defects on the TiNi structural phase transition has been described. IntroducingInvestigating diffusion processes in titanium nickelid alloys sharpened several issues on types and characteristic features of point defects. In the publication of Bastin and Riek [1] it was established that the chemical diffusion coefficient in TiNi is determined by Ni diffusion, and the activation energy for diffusion is too small (~1.4 eV) compared to other B2 intermetallic compounds. Investigating Ni diffusion in relation to pressure [2] showed that activation volume of diffusion Ni in TiNi within experimental error is equals zero. This could imply that diffusion mechanism is interstitial mediated or that there are structural vacancies in the intermetallic compound. Diffusion mechanism in TiNi is a particular case to explain the common diffusion mechanism in B2 intermetallic compounds. As discussion of the diffusion mechanism in B2 intermetallic, causes disputes [3][4][5], research of point defects in TiNi is relevant. Besides, some authors [6][7][8][9] state that point defects configuration of a B2 phase can play an important role in nucleation and growth processes of martensitic phase. Vacancy formation energy in titanium nickelidIn AB compounds with B2 structure interatomic potentials of identical atoms AA and BB have distinct dependency on the distance between identical atoms in given coordination sphere; further, interatomic potentials of these identical atoms also have a different potential well [9]. This results in the fact that the vacancy formation energy (E v ) on the different atomic sublattices is non-identical, which, in its turn, could be revealed in some B2 compounds by the positron annihilation spectroscopy (PAS) method [10].Presently, investigations in measurement the vacancy formation energy in a series of intermetallic compounds In the reference well-annealed state average positron lifetime corresponds to a delocalized positron state, i.e. the vacancy concentration in a sample lower than the PAS method threshold limit. Further, when heating the a Corresponding author: abat@ispms.tsc.ru

On the Effect of Hydrogen on the Low-Temperature Elastic and Anelastic Properties of Ni-Ti-Based Alloys

“…When considering that the amplitude hysteresis is strongly diminished after dehydrogenation, the mobile point defects can be associated with interstitial hydrogen. The temperature range of the point-defect mobility is another point in favour of hydrogen, since other point defects (for example, vacancies or oxygen interstitials) can hardly be mobile at such low temperatures [ 32 , 33 ]. The data of Figure 7 allow us to discard another possible mechanism of the reversible amplitude hysteresis of the IF, namely the heating of samples by high-amplitude oscillations.…”