The Irreversible Critical Range in the TiNi Transition

Abstract

Through an investigation of the transport and related thermodynamic properties of TiNi at and around its ``martensitic'' transition temperature, the existence of a critical range extending over a 60°C interval is established. Within this critical range, the phase transition is second order. Irreversibility of various properties within the critical range is interpreted in terms of irreversible shear movement of atoms. On the basis of transport data, the band structure of TiNi is inferred to be a single or ``nearly'' single positive band within the temperature range investigated. The postulate that some of the valence electrons undergo a ``covalent''→``conduction'' electronic transformation in the course of the second-order transition is consistent in large measure with experimental data.

Avoiding error of determining the martensite finish temperature due to thermal inertia in differential scanning calorimetry: model and experiment of Ni–Ti and Cu–Al–Ni shape memory alloys

“…The martensitic transformation temperatures (Ms, Mf, As, and Af) are indicated by arrows in the figures. They were determined in the same way as in the previous studies using those alloys [16,29,30,[32][33][34][35][36]. The present results are listed in Table 1.…”

“…Copper lead wires were spot welded to both ends and a K-type thermocouple to the center of gauge part. Therefore, no thermal effect should be involved in the measurement [10,14,22,29]. The rate of heating/cooling was below 0.2 K min -1 .…”

“…As the reference method for the transformation temperatures, the electrical resistance [29] was measured with four-point method. The dimension of the Cu-Al-Ni sample was a rectangle of 40 mm in length and 2.5 mm in width and 0.5 mm in thickness, and that of Ni-Ti alloy a wire of 40 mm in length and 0.6 mm in diameter.…”

“…This method was proposed in early works [29], examined by several researchers and has been adopted in some industrial standards [18,19]. Since the Mf measured with this method in DSC may include the error due to thermal inertia, we hereafter use the symbol Mf * to distinguish it from the real value of the Mf.…”

Anomalous Mechanical Properties of URANIUM-7.5 Weight Percent NIOBIUM-2.5 Weight Percent Zirconium Alloy.

“…This hypothesis is the simplest explanation of th~ observed data, but the possibility remains of a more complex structure, such as that reported for the titanium-nickel alloy. (8) It is apparent that crystallographic. studies, especially under stress, are needed to.…”