On the deformation response and cyclic stability of Ni50Ti35Hf15 high temperature shape memory alloy wires

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

“…Ni-rich TiNiHf alloys are too brittle to be plastically deformed. The first attempt to plastically deform a Ni-lean TiNiHf alloy was made by Kockar et al, [21] in which ECAE was employed to process Ti 42 [124] Afterward, the effect of thermomechanical treatment through cold and warm rolling, followed by post-annealing, on the shape recovery properties of the Ti 30 Ni 50 Hf 20 alloy was systematically investigated. [122] The results showed that cold rolling without intermediate annealing could produce the maximum possible thickness reduction, of %15%, before surface cracks were visible.…”

“…The stable transformation, characterized by large transformation strain and small irrecoverable strain, was obtained as a result of grain refinement and work hardening. More recently, a hot extruded Ti 35 Ni 50 Hf 15 alloy bar was successfully drawn into 0.75 mm wire with intermediate annealing at 700 °C . Afterward, the effect of thermomechanical treatment through cold and warm rolling, followed by post‐annealing, on the shape recovery properties of the Ti 30 Ni 50 Hf 20 alloy was systematically investigated .…”

On the Importance of Structural and Functional Fatigue in Shape Memory Technology

“…Only a few exceptions exist, for example in b-Ti alloys, where x-phase and a-Ti, which form during aging at elevated temperatures, affect martensitic transformations, e.g., [77][78][79][80]. In general, transformation-induced degradations can occur during (1) thermal cycling [81,82], (2) thermal cycling under stresses [83][84][85], and (3) during mechanical (e.g., pull-pull) cycling of pseudoelastic SMAs [86,87]. In the early 1970s, Perkins [88] provided microstructural evidence for irreversible transformationrelated microstructural changes, which result in functional degeneration.…”

Microstructural evolution and functional fatigue of a Ti–25Ta high-temperature shape memory alloy

“…Today, most of the HTSMAs are based on the nickel-titanium system, where the phase transformation temperature has been shifted up by alloying with ternary elements, such as Pt, [1][2][3][4][5] Pd, [1][2][3][4]6 and Hf. [7][8][9][10][11] The current approaches either call for high amounts of expensive noble elements or often result in systems with poor workability. 7,8 It should be noted, however, that for Ni-Ti-Hf HTSMAs the workability issue can be overcome by appropriate processing, and even thin wires can be produced as successfully demonstrated lately.…”

“…7,8 It should be noted, however, that for Ni-Ti-Hf HTSMAs the workability issue can be overcome by appropriate processing, and even thin wires can be produced as successfully demonstrated lately. 11 Lately, titanium-tantalum has been identified as a system that features substantial transformation strains from a martensitic phase transformation occurring at elevated temperature. 12,13 Moreover, Ti-Ta alloys are composed of reasonably priced constituents and demonstrate good workability.…”