Improvement of a Ti50Pd30Ni20 high temperature shape memory alloy by thermomechanical treatments

The tensile behavior of Ti36Ni49Hf15 high temperature shape memory alloy

“…1 shows a series of stress-strain (S-S) curves obtained at different temperatures for the Ti 36 Ni 49 Hf 15 alloy, in which (a)-(f), (h)-(n) and (g) correspond originally to the full martensite, the full parent phase and two phases coexisted matrix structures. The feature of the present S-S curves is similar to that of Ti-Ni-Pd [9] and cold-worked TiNi [10] shape memory alloys, but quite different from that of annealed TiNi shape memory alloys [11]. As well-known [12], when TiNi alloys, solution-treated or annealed after cold-working, are deformed in a martensitic state, the reorientation of martensite variants and/or detwinning occurs and the corresponding S-S curve exhibits a well defined yielding, a stress plateau with little work hardening and a Lüder's strain of about 8% before rapid work hardening; similar stress-strain behavior could also be observed when they are deformed in a parent phase state, with the deformation mechanism being the stress induced martensitic transformation.…”

“…This value is obviously smaller than that for NiTi alloys but bigger that for NiAl [17] and Ti-Pd-X (X ϭ Cr, Fe, Ni etc.) alloys [9,13,18]. The high critical stress for the reorientation of martensite variants and high work hardening are clearly to be responsible for the shape memory effect inferior to those of TiNi alloys.…”

Destabilization of Ni–Mn–Ga martensite: Experiment and theory

“…A number of reports about the compressive stressstrain tests of single crystals and polycrystalline Ni-Mn-Ga HTSMAs, showing improved plasticity, good shape recovery and thermal cycling stability, have been already presented [5,7,11,13,14,17]. The reported data point towards some advantages in the functional behaviour of these materials in comparison to the traditional Cu-, NiAl-, Zr-, NiTi(Zr,Hf)-and TiPd-based HTSMAs [19][20][21][22].…”

Characterization of Ternary NiTiPd High-Temperature Shape-Memory Alloys under Load-Biased Thermal Cycling

“…The most notable exceptions are more recent studies by Cai et al [12] on Ni 19.4 Ti 50.6 Pd 30 , Noebe et al [13] on Ni 19.5 Ti 50. 5 Pd 30 , and Kumar et al [14] on Ni 10 Ti 50 Pd 40 . These studies were predominantly limited to higher Pd containing alloys.…”

“…[8] Several methods were proposed for improving the shape recovery of these alloys by strengthening the material against plastic deformation. These included alloying with boron, [9] heat treatment resulting in the precipitation of Ti 2 Ni type phases, [6] and thermomechanical processing, which consisted of either cold rolling and subsequent heat treatment [10] or isothermal mechanical cycling. [11] Despite all the work performed on the NiTiPd system, there has been limited research investigating the shapememory response of these alloys under an applied load, which would be much more relevant to their use as solid-state actuators than measuring stress-free recovery.…”