Poisson ratio of TiNi

Abstract

A review of the literature data and methods for calculating the Poisson coefficient of the TiNi intermetallic compound in the poly- and single-crystal state is performed. The results of our own research are also presented. Significant variability of the presented data is noted, due to differences in the thermomechanical processing of the alloys and the measurement and calculation methods used. By averaging the matrices of elastic constants and compliance coefficients using the Voigt, Reuss, and Hill approximations, we obtained the values of the parameters of the effective elastic properties of TiNi polycrystals and calculated the Poisson’s ratio. Using analytical expressions to calculate the values of the extreme values, the extrema of the Poisson’s ratio of cubic TiNi crystals are determined for standard orientations. Based on a number of data, TiNi crystals are auxetics (materials having negative Poisson’s ratio values), on the basis of others they are not. We found that TiNi crystals belong to the so-called partial auxetics, in this case the signs of the inequalities (s12 < 0, s = s11 + s12 − s44/2 > 0 or s12 > 0, s = s11 + s12 − s44/2 < 0) are opposite. The values of the Poisson’s ratio TiNi averaged over the transverse directions of deformation are analyzed. Isosurfaces of the Poisson’s ratio and their sections are presented using the ELATE computational graphic package and the MATHCAD computer algebra program. Aspects of TiNi elastic anisotropy, its parameters, and their relationship with martensitic transformations in TiNi and alloys based on it are discussed.