Investigation and Composition Characterization of a “NiTi-like” Alloy Combining High Temperature Shape Memory and High Entropy

Abstract

New high temperature shape memory alloys with five or more elements are under development and present attractive performances for several functional applications. These active metallic materials are called high entropy and high temperature shape memory alloys (HE-HT-SMAs). This work deals with the characterization of an alloy that combines high temperature shape memory effect and high entropy effect features, a NiCuTiHfZr alloy. The evolution of the phase transformation and the shape memory effect during thermal fatigue was compared with a ternary alloy NiTiZr. Ingots were prepared in a cold crucible and alloys were characterized after thermal cycling at 600 K without a protective gas atmosphere. Optical microscope, X-ray diffraction, and scanning electron microscopy observations showed the presence of martensite in this unpublished alloy at room temperature. The differential scanning calorimetry (DSC) tests showed that martensitic transformation takes place at high temperature. High temperature thermal cycling was performed during a three-point bending tests under constant load without a protective atmosphere. Thermomechanical results showed that high entropy effects increase the operating behavior at high temperature. Hence this new composition of NiCuTiHfZr alloy can be used as an actuator for aerospace and aeronautic application.

Relationship between Chemical Composition and Ms Temperature in High-Entropy Shape Memory Alloys

“…The published works by Piorunek et al [11,17] show indeed that for the same composition, the M s transformation temperature evolves according to the stages of solution treatment of the intermetallics. It should be pointed out in this paper all the studied alloys are assumed to be homogenized and the contribution of the intermetallics is neglected since it does not exceed 5% as stated in our previous work [28]. The second aspect is related to the specific mixing entropy (DSmix/R), ranging between 1.3 and 1.75, where R is the gas constant [29,30].…”

“…( 7) for NiTi-like and TiNb-like alloys. These two alloys have been chosen according to the different criteria proposed in [13] and [19]. The two alloys have been heat-treated to be homogenized and solutioned.…”

“…The M s temperatures of the other studied HE-SMAs are summarized in Table 1. It is important to emphasize that the whole HE-SMAs presented in the database have different types and different chemical compositions: NiTi-like [5,[11][12][13][14][15][16][17][18], TiNb-like [19], NiAl-like [20,21], CuAl-like [22] and FeAl-like [23,24]. In addition, it should be noted that all the alloys selected to enrich the database, either specifically developed for the study or taken from the open literature, are in the same metallurgical state (Solution Treatment or ST).…”

Effect of Valence Electron Concentration in High Entropy Shape Memory Alloys/ Review

“…From the table (Table 1), we see that the values of VEC are between 6 to 8 electrons per atom in general. In a study by (Peltier et al, 2020) by increasing the atomic percentage of Ti and because the valence electron number in Ti is four, the samples (24, 25, and 26) VEC value's decreased to around six. The same case is valid for samples (33, 34, and 35) where the percentage of each of (Ti, Zr, and Hf) increased compared to the other elements.…”

Martensite Transformation and Superelasticity at High Temperature of (TiHfZr)74(NbTa)26 High-Entropy Shape Memory Alloy

“…The alloy exhibited stress transformation up to 1200 MPa at a higher temperature. These previous alloys are known as ''NiTi-like alloys'' [10]. Wang et al [11] have developed a TiNbAl-like alloy that exhibits superelastic behavior at room temperature with a recoverable strain around 5%, by optimizing thermal treatments and Nb content of the TiZrHfAlNb high-entropy alloy.…”