Measurement of elastic constants of monoclinic nickel-titanium and validation of first principles calculations

Polycrystalline, monoclinic nickel-titanium specimens were subjected to tensile and compressive deformations while neutron diffraction spectra were recorded in situ. Using these data, orientation-specific and macroscopic Young's moduli are determined from analysis of linear-elastic deformation exhibited by 13 unique orientations of monoclinic lattices and their relationships to each macroscopic stress and strain. Five of 13 elastic compliance constants are also identified: s11 = 1.15, s15 = −1.10, s22 = 1.34, s33 = 1.06, s35 = −1.54, all × 10−2 GPa−1. Through these results, recent atomistic calculations of monoclinic nickel-titanium elastic constants are validated.