Shape memory alloy design from first principles: calculating properties of Ni-Ti-based ternary alloys within a multi-scale collaboration

Abstract: While the electronic foundations of shape memory behavior in NiTi have been thoroughly examined and elucidated,[1,2] we extend this understanding to ternary alloys by taking a multi-scale approach to materials design. Using ab initio calculations, the effect of ternary additions on the martensitic behavior of NiTi is investigated by applying the highly precise FLAPW method to the Ni-Ti-X(X=Pt, Pd; 0-50system. We determine ternary element site preferences, pair interaction energies, and the energy hierarchy among the phases, finding that Pd and Pt atoms replace Ni and decorate the lattice at second and third nearest neighbors from one another, respectively. By calculating detailed elastic properties, cleavage energies, and planar generalized stacking fault energetics, we explain brittle/ductile behavior in the system, identify slip systems, and find that the C' elastic constant becomes unstable with increased alloying. Additionally, we establish how ternary elements affect the physics governing martensitic behavior by tracing changes in Fermi surface nesting behavior to mechanical instabilities and identifying unstable atomic vibration modes through imaginary branches of calculated phonon dispersions. As this work is embedded within a multi-scale experimental and theoretical approach in which these first principles results are used as inputs for continuum and micro-mechanical modeling techniques, the challenges and possibilities of this collaboration will be discussed.

[1] Phys Rev B, 80, 144203
[2] Phys Rev B, 79, 020202(R)

The seminar takes place at 2:00 p.m. in the ICAMS seminar room UHW 11/1102, Stiepeler Straße 129, 44801 Bochum.

For further information contact Bernhard Eidel, bernhard.eidel@rub.de.