Premartensitic Phases of Ti sub 50 Ni sub 47 Fe sub 3

• Published in: Physical review. B, Condensed matter Condensed matter, 1985-06, Vol.31 (11), p.7306-7315
• Main Authors: Salamon, M B, Meichle, M E, Wayman, C M
• Format: Article
• Language: English
• ISSN: 0163-1829

The addition of small amounts of Fe to the shape-memory alloy Ti--Ni suppresses the martensitic transition, permitting a detailed study of "premartensitic" effects. Using X-ray and neutron-diffraction data, specific-heat, resistivity, and susceptibility measurements, it is shown that two distinct phases appear. The first occurs at T sub I = 232K in a sample containing 3.2 at.% Fe and is characterized by superlattice reflections near (1/3, 1/3, 1/3) and (1/3, 1/3, 0) positions. These are incommensurate, but are commensurate reflections on a rhombohedral "ghost" lattice, but with the main Bragg peaks centered at the original cubic positions. At T sub r = 224K for this alloy, a rhombohedral phase appears such that the Bragg peak in the unique direction lies on the "ghost" reciprocal lattice. Thus, the host lattice distorts to accommodate the wave vector of the modulation that produces the superlattice reflections. A model is proposed that involves discommmensurations in the lattice strain, analogous to discommensurations in the charge-density-wave phase, to explain the "ghost" lattice effect. 34 ref.--AA