Structural stabilities, elastic constants, generalized stacking fault energetics, and the martensitic transformation mechanisms for the Ni_50−xTiPt_x (x = 0 − 30) ternary system: ab initio investigation

Abstract
To determine the effect of ternary additions on the martensitic behavior of NiTi, we apply ab initio calculations using the highly precise full-potential linearized augmented plane wave method to the Ni-Ti-Pt system. We compare formation energies of various stoichiometries and the pair energetics between Pt atoms to create a numb er of model austenite structures, finding that Pt atoms prefer to decorate the lattice at third nearest neighbors from one another, and establish the hierarchy among the austenitic and martensitic phases. We examine the structural stability to determine the susceptibility toward displacive phase transformation: namely, we calculate planar generalized stacking fault energetics of major shear planes including the {100}, {011}, and {111} planes and we calculate and compare the elastic constants of each phase. We show that increased Pt content causes a dramatic softening of the austenite C′ elastic constant and increased rigidity in the martensite, and there is a high resistance to {100} shear similar to equiatomic NiTi. Finally, we explore a martensitic mechanism of this alloy and explain how the transformation path and energy barriers of the NiTi system are affected by Pt.