Martensitic phase transformation and shape memory properties of the as-cast NiCuTiHf and NiCuTiHfZr alloys

Cyclic Stability of Ni44.8Cu5Ti45.2Hf5 and Zr‐Substituted Ni44.8Cu5Ti40.2Hf5Zr5 Medium‐Entropy Shape Memory Alloys

“…In the case of this study, the formation of (Ti,Hf,Zr)‐rich Ti2Ni‐type precipitates enriches the surrounding matrix in Ni and Cu, eventually leading to lower transformation temperatures for Zr‐free and Zr‐5 alloys as compared to those predicted by the correlation proposed by Zarinejad et al [ 1,2 ] This effect is more pronounced in the case of Zr‐5 alloy because the fraction of secondary Ti‐rich phase is higher in this alloy. [ 16 ] This rationalizes why substituting 5 at% Zr for Ti in Ni44.8Cu5Ti45.2Hf5 alloy significantly decreases its transformation temperatures.…”

“…Oxygen‐stabilized Ti 2 Ni‐type phase forms during solidification of the alloy and it remains after solution annealing treatment. [ 16 ] The inconsistency between the CALPHAD predictions and experimental observations arises because oxygen contamination is not taken into account in the CALPHAD description of the (Ni,Cu)(Ti,Hf/Zr) system. Oxygen contamination originates mainly from processing‐related factors, most important ones include impurities associated with raw materials and/or unavoidable small‐scale leakage during arc melting.…”

“…Details concerned with tensile test specimen preparation and constant‐stress thermal cycling experiments have been described elsewhere. [ 16 ] Pseudoelastic responses of the alloys were examined upon cyclic tensile loading–unloading at temperatures above A f with strain rates of 5 × 10 −3 , 2.5 × 10 −2 , and 10 −1 s −1 .…”

“…In our recent research, [ 16 ] two SMAs from the quasibinary (Ti,Hf/Zr) 50.2 (Ni,Cu) 49.8 system were introduced and their microstructures, phase transformation behaviors, and SME/PE responses were evaluated in the as‐cast state. In the quaternary alloy, Ti and Ni were substituted by 5 at% Hf and 5 at% Cu, respectively.…”

Functional and Mechanical Properties of As-Deposited and Heat Treated WAAM-Built NiTi Shape-Memory Alloy

“…Such a group has gained interest from industry and scientists over the years due to its superior properties and the possibility to develop new automotive, aerospace, medical, and robotics applications. This group includes a wide variety of materials [1][2][3][4][5], but NiTi-based alloys have the best combination of characteristics compared with the others [6]. For the first time, in 1963, Buhler et al discovered the unique shape-memory effect of a close-to-equiatomic NiTi alloy [7].…”