Crystal size induced reduction in thermal hysteresis of Ni-Ti-Nb shape memory thin films

Abstract

Ni41.7Ti38.8Nb19.5 shape memory alloy films were sputter-deposited onto silicon substrates and annealed at various temperatures. A narrow thermal hysteresis was obtained in the Ni-Ti-Nb films with a grain size of less than 50 nm. The small grain size, which means an increase in the volume fraction of grain boundaries, facilitates the phase transformation and reduces the hysteresis. The corresponding less transformation friction and lower heat transfer during the shear process, as well as reduced spontaneous lattice distortion, are responsible for this reduction of the thermal hysteresis.

Low temperature annealing effects on martensitic transformation and exchange bias behavior of Ni–Mn–Sn free-standing alloy thin films

“…Moreover, when the grain size is less than 4.3 nm, large amount of grain boundaries will promote the phase transformation since there are more defects, and the phase transformation is easier to occur there. 31,32 This would facilitate the martensitic transformation and the reverse transformation, resulting in a narrow thermal hysteresis, as shown in inset of Fig. 4(b) and (c).…”

Investigation of the superelastic behavior of a Ti-16Zr-13Nb-2Sn sputtered film by nanoindentation

“…Film technology is promising for further miniaturization and design possibilities for nanometer-sized functional tools and devices for biomedicine. In the field of superelastic films, most activities have focused on the superelastic response of magnetron sputtered NiTi-base alloy films since the 1990s, basically for the development of miniature systems (micro-sensors, − actuators, − pumps and -valves) [15][16][17][18]. Beside the suspected toxicity and carcinogenicity of nickel, a major drawback is the amorphous nature of asdeposited NiTi films at room temperature which required suitable heat superelastically.…”

Electronic Mechanism of Martensitic Transformation in Nb-doped NiTi Alloys: A First-Principles Investigation

“…NiTiNb SMAs have received considerable attention in recent decades owing to their excellent shape memory effect, high damping capacity, good mechanical properties, sufficient corrosion resistance, and wide transformation hysteresis, which have potential for a wide range of engineering applications such as pipe coupling or sealing. 6 − 13 …”

“…Because of the very low yield strength of NiTi in the martensite state, the application of NiTi alloys as a high-strength damping material has been limited. NiTiNb SMAs have received considerable attention in recent decades owing to their excellent shape memory effect, high damping capacity, good mechanical properties, sufficient corrosion resistance, and wide transformation hysteresis, which have potential for a wide range of engineering applications such as pipe coupling or sealing. − …”