On the Impact of Texture and Grain Size on the Pseudoelastic Properties of Polycrystalline Fe–Ni–Co–Al–Ti Alloy

The effects of thermomechanical treatments on crystallographic texture and grain size evolution and their impact on the pseudoelastic properties in Fe41–Ni28–Co17–Al11.5–Ti2.5 (at.%) were studied in the present paper. The results show that cold rolling leads to brass-type texture in this alloy, which is typical for low stacking fault energy materials. Thermal treatments up to 1300 °C were conducted and it is shown that the presence of β-phase helps to control grain growth. After the dissolution of the secondary phase induced by heat treatment at higher temperatures, a strong {230}〈001〉 recrystallization texture evolves in cold rolled samples already upon imposing medium reduction ratios. Finally, good pseudoelastic properties are found in conditions being characterized by adequate texture and grain sizes spanning over the entire thickness of the samples tested.Fil: Sobrero, Cesar Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lauhoff, C.. University of Kassel; AlemaniaFil: Wegener, T.. University of Kassel; AlemaniaFil: Niendorf, T.. University of Kassel; AlemaniaFil: Krooß, P.. University of Kassel; Alemani

Cyclic degradation of titanium-tantalum high-temperature shape memory alloys - The role of dislocation activity and chemical decomposition

Titanium-tantalum shape memory alloys (SMAs) are promising candidates for actuator applications at elevated temperatures. They may even succeed in substituting ternary nickel-titanium high temperature SMAs, which are either extremely expensive or difficult to form. However, titanium-tantalum alloys show rapid functional and structural degradation under cyclic thermo-mechanical loading. The current work reveals that degradation is not only governed by the evolution of the ω-phase. Dislocation processes and chemical decomposition of the matrix at grain boundaries also play a major role.DFG/NI1327/3-1DFG/MA1175/34-1DFG/EG101/22-1DFG/FR2675/3-

Additive Manufacturing of Binary Ni–Ti Shape Memory Alloys Using Electron Beam Powder Bed Fusion: Functional Reversibility Through Minor Alloy Modification and Carbide Formation

Shape memory alloys (SMAs), such as Ni–Ti, are promising candidates for actuation and damping applications. Although processing of Ni–Ti bulk materials is challenging, well-established processing routes (i.e. casting, forging, wire drawing, laser cutting) enabled application in several niche applications, e.g. in the medical sector. Additive manufacturing, also referred to as 4D-printing in this case, is known to be highly interesting for the fabrication of SMAs in order to produce near-net-shaped actuators and dampers. The present study investigated the impact of electron beam powder bed fusion (PBF-EB/M) on the functional properties of C-rich Ni50.9Ti49.1 alloy. The results revealed a significant loss of Ni during PBF-EB/M processing. Process microstructure property relationships are discussed in view of the applied master alloy and powder processing route, i.e. vacuum induction-melting inert gas atomization (VIGA). Relatively high amounts of TiC, being already present in the master alloy and powder feedstock, are finely dispersed in the matrix upon PBF-EB/M. This leads to a local change in the chemical composition (depletion of Ti) and a pronounced shift of the transformation temperatures. Despite the high TiC content, superelastic testing revealed a good shape recovery and, thus, a negligible degradation in both, the as-built and the heat-treated state

Cyclic Superelastic Behavior of Iron-Based Fe-Ni-Co-Al-Ti-Nb Shape Memory Alloy

Iron-based shape memory alloys came into focus as promising candidate materials for large-scale structural applications owing to their cost-efficiency. In the present work, the superelastic properties of a recently introduced Fe-Ni-Co-Al-Ti-Nb shape memory alloy are investigated. For 〈001〉-oriented single-crystalline material in aged condition (650 °C/6 h), an incremental strain test reveals excellent superelasticity at −130 °C with fully reversible strains up to about 6%. Under cycling loading at different test temperatures, however, the alloy system investigated suffers limited functional stability.Fil: Lauhoff, C.. University of Kassel; AlemaniaFil: Remich, V.. University of Kassel; AlemaniaFil: Giordana, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Sobrero, Cesar Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Niendorf, T.. University of Kassel; AlemaniaFil: Krooß, P.. University of Kassel; Alemani

Functional Properties of Highly Textured Fe–Ni–Co–Al–Ti–B Shape Memory Alloy Wires

The effect of thermomechanical treatments on grain size and precipitate evolution as well as their impact on the shape memory properties of cold-drawn Fe$_{41}$–Ni$_{28}$–Co$_{17}$–Al$_{11.5}$–Ti$_{2.5}$–B$_{0.05}$ (at. %) wires were studied. Cold drawing produces a strong {hkl}  /{hkl}  texture in this alloy. Different thermal treatments promote the evolution of specific recrystallisation textures as well as grain growth, while ageing at 600 °C to 650 °C leads to the formation of γ’ precipitates. Variation in size and distribution of the precipitates via ageing significantly affect the functional properties. A maximum transformation strain of 1.3% without fracture was obtained on sample tested on heating–cooling experiments