Tensile shape memory behavior of Ni50.3Ti29.7Hf20 high temperature shape memory alloys

Abstract

The effects of heat treatment on the shape memory characteristics of a polycrystalline Ni 50.3 Ti 29.7 Hf 20 alloy were studied via thermal cycling under stress and isothermal stress cycling experiments in tension. It was revealed that transformation temperatures could be increased above 100 °C with aging at temperature above 500 °C and in particular were stabilized against stress-free thermal cycling after aging at 500 °C. Recoverable strain of ~5% was observed for the as-extruded samples and decreased to ~4% after aging due to the formation of non-transformable precipitates. The aged alloys demonstrated near perfect shape memory effect under tensile stresses as high as 700 MPa and perfect superelasticity at temperatures up to 230 °C. Finally, the tension-compression asymmetry observed in NiTiHf alloys was discussed.

Recent Development of TiNi‐Based Shape Memory Alloys with High Cycle Stability and High Transformation Temperature

“…[96] Further study indicates that this asymmetry results from martensite ordering, the unidirectional nature of the habit plane, and the number of corresponding variant pairs activated during transformation. [120] From a physical metallurgical point of view, the shape recovery properties of SMAs can be optimized by increasing the critical stress for slip. Several strengthening methods have been demonstrated to be suitable for TiNiHf-based alloys, including precipitation strengthening, [74,92,96,121] solid-solution strengthening using quaternary elements, [99,104] grain refinement, [21] and work hardening.…”

“…[120] The authors claim that this is partially due to precipitation of the H-phase, which reduces the volume fraction of materials taking part in phase transformation. [120] 3.…”

Fabrication and Characterization of Freestanding NiTi Based Thin Film Materials for Shape Memory Micro-actuator Applications

“…Several precipitates in the NiTiHf system exist that hinder phase transformation, e.g., Ti 2 Ni(Hf), HfNi(Ti), Hf 2 Ni(Ti), thus limiting the transformation region of the alloy to Ni contents [ 40 at.%, and Hf contents \ 30 at.% [25]. In Nirich NiTiHf alloys precipitates were found to play a crucial role to increase the material strength, and to obtain a near perfect dimensional stability during compression tests as well as a low thermal hysteresis [62]. Finely dispersed c DSC measurement of a sputtered NiTiHf film reveals a 100 K hysteresis width, and a M f temperature of 115°C small precipitates are beneficial since they act as pinning sites against dislocation movement.…”

Wind Tunnel Research on the Unmanned Aerial Vehicle Rotor Blade Setting Angle

“…Morphing is a technology, inspired by nature, dedicated to the next generation of aircraft. Unmanned aerial vehicles can provide a safe platform for testing intelligent materials which are becoming increasingly popular [7,20,25]. The works [28,29] present the preliminary results of the tests of the main rotor designed to be integrated with the blades with a variable blade setting angle.…”