First-principles screening of structural properties of intermetallic compounds on martensitic transformation

Abstract

Martensitic transformation with good structural compatibility between parent and martensitic phases are required for shape memory alloys (SMAs) in terms of functional stability. In this study, first-principles-based materials screening is systematically performed to investigate the intermetallic compounds with the martensitic phases by focusing on energetic and dynamical stabilities as well as structural compatibility with the parent phase. The B2, D0 3 , and L2 1 crystal structures are considered as the parent phases, and the 2H and 6M structures are considered as the martensitic phases. In total, 3384 binary and 3243 ternary alloys with stoichiometric composition ratios are investigated. It is found that 187 alloys survive after the screening. Some of the surviving alloys are constituted by the chemical elements already widely used in SMAs, but other various metallic elements are also found in the surviving alloys. The energetic stability of the surviving alloys is further analyzed by comparison with the data in Materials Project Database (MPD) to examine the alloys whose martensitic structures may cause further phase separation or transition to the other structures.

Solution effect on improved structural compatibility of NiTi-based alloys by systematic first-principles calculations

“…%), respectively. Note that the B2 structure of the binary equiatomic NiTi is known to be dynamically unstable at 0 K, 11,[14][15][16][25][26][27][28][29][30] which indicates that we also need to carefully model the B2 structure of the binary nonstoichiometric Ni-Ti and the ternary Ni-Ti-X alloys not to break their expected atomic configurations. The current one-atom-replaced supercell models still have crystallographically high symmetries, and hence we can keep the expected atomic configurations of the B2 structure because of the symmetry constraint during the structural optimization.…”

“…In particular, it may be necessary for the martensitic-phase structure to have lower energy than the B2 structure at 0 K to guarantee the existence of martensitic transformation between the B2 parent-phase structure at high temperature and the B19 or B19 0 martensitic-phase structure at low temperature. 25 To ensure that the considered martensitic transformations occur in reality, it may also be better for the energetically favorable martensitic-phase structure between the B19 and B19 0 structures to be energetically more stable than other possible states. It is well known that the convex-hull states of the binary Ni-Ti systems consist of NiTi, NiTi 2 , and Ni 3 Ti.…”

“…23. The B2 structure of the binary equiatomic NiTi is actually known to be dynamically unstable at 0 K, 11,[14][15][16][25][26][27][28][29][30] and a small amount of alloying may not change this dynamical instability. The converged structures without any symmetry constraints may therefore be far away from the B2 structure for some Ni-Ti-X alloys.…”

“…The energies of the martensitic-phase structures should be lower than that of the B2 parent-phase structure to enable the martensitic transformation. 25 Therefore, to consider the possibility for use as SMAs, the Ni-Ti-X alloys should satisfy the conditions E B19 0 -E B2 < 0 or E B19 -E B2 < 0. An energy tolerance of 0.001 eV/atom was used to exclude the alloys in which the martensitic structures converged into the B2 structures.…”

“…It is found that 26 Ni-Ti-X alloys satisfy 25 and Ni 50 Ti 37.5 X 12.5 with X = Ru, Rh, Ir, or Pt, the alloyed element X energetically prefers to occupy the rich-element site, creating the rich-element antisite rather than occupy the deficient-element site in either or both the B2 parent-phase and martensitic-phase structures. For these alloys, further investigation on the structural compatibility between the parent-phase and martensitic-phase structures may be needed using, for example, the models including the antisite.…”