First-Principles Calculations of Structural, Mechanical, and Electronic Properties of the B2-Phase NiTi Shape-Memory Alloy Under High Pressure

Abstract

A first-principles calculation program is used for investigating the structural, mechanical, and electronic properties of the cubic NiTi shape-memory alloy (SMA) with the B2 phase under high pressure. Physical parameters including dimensionless ratio, elastic constants, Young’s modulus, bulk modulus, shear modulus, ductile-brittle transition, elastic anisotropy, and Poisson’s ratio are computed under different pressures. Results indicate that high pressure enhances the ability to resist volume deformation along with the ductility and metallic bonds, but the biggest resistances to elastic and shear deformation occur at P = 35 GPa for the B2-phase NiTi SMA. Meanwhile, the strong anisotropy produced by the high pressure will motivate the cross-slip process of screw dislocations, thereby improving the plasticity of the B2-phase NiTi SMA. Additionally, the results of the density of states (DOS) reveal that the B2-phase NiTi SMA is essentially characterized by the metallicity, and it is hard to induce the structural phase transition for the B2-phase NiTi SMA under high pressure, which provides valuable guidance for designing and applying the NiTi SMA under high pressure.

DFT investigation of the dissolution trends of NiTi alloys with the B2 and B19′ phases during the initial oxidation stage

“…The calculated lattice constants are a = b = c = 3.010 Å and a = b = g = 901 for NiTi-B 2 and a = 2.945 Å, b = 4.003 Å, c = 4.953 Å, a = g = 901, and b = 108.4091 for NiTi-B19 0 . These results are in good agreement with previously reported experimental and theoretical results, 4,[35][36][37][38] which verifies the reliability of our calculation methods. A symmetrical slab model with 2 Â 2 unit cells including five atomic layers was sufficient for avoiding interactions among the atoms of the outermost atomic layers and the NiTi-B 2 (110) and NiTi-B19 0 (010) surfaces.…”

Measurement Modulus of Elasticity Related to the Atomic Density of Planes in Unit Cell of Crystal Lattices

“…Elastic constants are created in the relationship between stress and strain and they are dependent on the configuration of crystal lattice, therefore elastic constants are derived from planes in the crystal lattice [ 5 , 6 , 7 , 8 ]. Furthermore, there are several studies on the correspondence of elastic constants and planes/directions such as Ref [ 9 , 10 , 11 ]. Crystallographic planes that are equivalent have similar atomic planar densities.…”

“…Crystallographic planes that are equivalent have similar atomic planar densities. Planar density is the fraction of the total crystallographic plane area that it is occupied by atoms [ 9 ]. The planar density is a significant parameter of a crystal structure, and it is specified as the number of atoms per unit area on a plane [ 12 ].…”

High-throughput calculation of atomic planar density for compounds

“…The atomic arrangement within planes and, by extension, planar density (the number of atoms per unit area on a plane) are relevant to applications such as elasticity (Rabiei et al, 2020;, oxidation (Ahn et al, 2011), surface energy (Wang, 2020), thermoelectrics (Snyder & Toberer, 2008), nanoscale materials patterning (Liu et al, 2016) and magnetism (Williams, 1937), all of which can exhibit anisotropy with respect to crystallographic direction: e.g. bulk modulus (Fine et al, 1984;Holec et al, 2012;Yu & Liu, 2019).…”