Transformation temperature changes due to second phase precipitation in NiTi-based shape memory alloys

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

“…The number of valence electrons can be calculated based on the contributions of the s + d electrons from the transition metals, or the s + p electrons of the non-transition metals [12]. Since both Zr and Cu are transition metals, the number of valence electrons ( e v ) for Zr and Cu are 4(5s 2 4d…”

“…The d-d hybridization between Zr and Cu sites becomes stronger as the valence electron concentration increases, which increases the total energy; likewise as the stability of the B2 structure strengthens, M s decreases. Moreover, a higher valence electron concentration usually results in higher bulk and shear moduli, which for solid state materials is a measure of resistance to volume change and a measure of resistance to shape change, respectively [11][12][13]. In summary, higher c v values lead to lower transformation temperatures.…”

“…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.…”

Experimental Investigation of Isothermal Sections (1000, 1200 °C) in the Ni-Ti-Zr System

“…[2] Therefore, control of transformation temperatures of NiTi-based shape memory alloys is an important research subject to enhance the reliability and applicability of these functional materials. [3][4][5][6][7] For this reason, materials scientists have managed to develop NiTibased alloys with higher martensitic transformation temperature. [8] Furthermore, experiments have shown that with a small addion of Zr, the martensitic transformation temperature decreases.…”

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

“…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 .…”