Dependence of Transformation Temperatures of NiTi‐based Shape‐Memory Alloys on the Number and Concentration of Valence Electrons

Abstract

Dependence of transformation temperatures of ternary and quaternary NiTi‐based shape memory alloys on the number (ev/a) and concentration (cv) of valence electrons is investigated. Two distinct trends of transformation temperatures with respect to the number of valence electrons per atom are found depending on whether ev/a = 7 or ev/a ≠ 7. Clear correlations between transformation temperatures and cv exist. Ms and As decrease consistently from 900 to −100 °C, and 950 to −30 °C, respectively, with increasing cv from 0.145 to 0.296. The relationship of electron concentration on the elastic moduli of the NiTi‐based alloys is discussed. The possible influence of the atomic size of alloying elements on transformation hysteresis is introduced.

Design and Anchorage Dependence of Shape Memory Alloy Actuators on Enhanced Voiding of a Bladder

“…[1] This shape transformation is caused by atomiclevel structural changes in the material from the martensitic to the austenite phase at a specific temperature, [2] and applying voltage to the material is a method to induce heat www.advmattechnol.de when their bladder is full. Hence, we propose to integrate a force sensor with the device to find out the bladder filling volume.…”

Empirical mapping of ZrCu-based alloys with valence electrons versus transformation temperatures

“…Therefore, it is necessary to design the chemical composition of such materials to control the martensitic transformation temperatures, in order to acquire high transformation temperatures in HTSMA devices or to obtain B2 phase-BMG composites for applied use [9,10].The mechanism that allows alloying elements to change their transformation temperatures is dependent upon the electronic structures and the interatomic bonding forces within such alloys [11]. The valence electrons contributed by s + d electrons of the transition metals, or s + p electrons of the non-transition metals, act as adhesives during metallic bonding [12,13].…”

“…The valence electrons contributed by s + d electrons of the transition metals, or s + p electrons of the non-transition metals, act as adhesives during metallic bonding [12,13]. The strength of this adhesion, which depends on the number (e v /a), concentration (c v ), density (n) of valence electrons, is relevant to the transformation temperatures of SMAs [11][12][13][14][15][16]. For ZrCu-based alloys, the relationship between transformation temperature and electronic structure has yet to be quantified, and therefore a guiding empirical map is necessary to design and optimize the central properties in ZrCu-based alloys.…”

Nanoindentation of Annealed and As-Sputtered Thin Films of Nickel Titanium Shape Memory Alloys

“…An increase of nickel past the stoichiometric composition decreases the transformation temperature ( Figure 7) 31 . The decrease in the phase transition temperature with the increase in nickel concentration is due to the increase in valance electrons 32 . Nickel has ten valance electrons while titanium has 4 valence electrons.…”

“…The increase in nickel concentration increases the e v /a to greater than seven. The increase of valance electrons decreases the transition temperature as a result of the higher elastic constraint of the crystal, which increases the resistance against the shear that causes the phase transformation 32,33 . An increase of titanium past the stoichiometric composition has little effect to the transition temperature because excess titanium does not dissolve into NiTi and precipitates in the grain boundaries as NiTi 2 .…”