Novel Shape Memory Alloys: Session 6
Program Organizers: Othmane Benafan, NASA Glenn Research Center
Friday 10:20 AM
July 14, 2017
Location: Hyatt Regency Chicago
Session Chair: Matthias Boenisch, IFW-Dresden
Martensitic Transformation in Cu-Al-Ni-X Quaternary Shape Memory Alloys: Iñaki López-Ferreño1; Patricia Lorenzo1; Jose Fernando Gómez-Cortés1; Tomasz Breczewski1; María Luisa Nó1; Isabel Ruiz-Larrea1; Ángel López-Echarri1; Jose San Juan1; 1Universidad del Pais Vasco
Among the different families of shape memory alloys (SMAs), Cu-Al-Ni alloys have received attention due to their excellent properties at micro and nano-scale and their capacity to transform in a wide range of temperatures including 100ºC-200ºC range where there is a technological interest in developing shape memory alloys actuators. With the aim of improving different aspects of this ternary system, such as the thermal stability and welding properties, quaternary alloys have been designed. In the present work the influence of Sn, Ga, Mn and Au quaternary elements in the martensitic transformation temperatures has been studied. In addition, the more promising quaternary compositions have been chosen and single crystals have been growth via Bridgman method, and their thermo-mechanical behaviour has been studied.
Effects of Cr on Martensitic Transformation and Oxidation Resistance in Fe-Mn-Al-Ni Alloys: Yuki Noguchi1; Toshihiro Omori1; Ryosuke Kainuma1; 1Tohoku University
Fe-34Mn-15Al-7.5Ni(at%) alloy exhibits superelasiticity associated with the α (bcc) / γ (fcc) thermoelastic martensitic transformation due to the NiAl (B2) fine precipitates and shows small temperature dependence of critical stress for martensitic transformation. However, oxidation occurs in air atmosphere during processing, occasionally causing microstructural change after long heat treatment. Cr is expected to improve oxidation and corrosion resistance. In this work, we investigated the effects of Cr addition on the martensitic transformation and oxidation resistance. Fe-Mn-Al-Ni specimens with Cr contents ranging from 0 to 15% were prepared. The α single phase with the B2 precipitates was obtained up to 10% Cr. The martensitic transformation was thermoelastic and the transformation temperatures decreased with increasing Cr content. Moreover, superelasticity with smaller temperature dependence of critical stress was obtained and the oxidation resistance was improved by addition of Cr.  T. Omori et al., Science 333 (2011) 68.
Martensitic Transformation and Phase Evolution in Intermetallic 60NiTi Alloy under Tensile and Compressive Loading: Othmane Benafan1; Anita Garg2; Ronald Noebe1; Harley Skorpenske3; Ke An3; Norbert Schell4; 1NASA Glenn Research Center; 2University of Toledo; 3Oak Ridge National Laboratory; 4Institute of Materials Research, Helmholtz-Zentrum Geesthacht
Tensile and compressive deformation of a Ni-rich Ni55Ti45 (at.%) alloy, commonly known as 60NiTi (wt.%), was investigated by in situ neutron diffraction and electron microscopy. After solution treatment, the alloy showed remarkable strength and high hardness resulting from a high density of fine Ni4Ti3 precipitates, in spite of a water quench. Non-linear but reversible stress-strain behavior was observed in tension up to 1.5 GPa and was attributed to stress-induced martensite as revealed by neutron diffraction measurements. Transmission and scanning electron microscopy revealed stress-induced coarsening of Ni4Ti3 precipitates in both tension and compression tested samples; in addition, precipitation and growth of the stable Ni3Ti phase was observed after tensile testing. The equilibrium Ni3Ti phase appeared within grains and at grain boundaries leading to a source of early failure in tension. Potential ramifications of these structural/microstructural changes are discussed in regards to hydrospace and tribology applications such as gears and bearings.
Effect of Composition and Thermal Processing on Transformation Characteristics and Equilibrium Phase Stability in NiTiHf High Temperature Shape Memory Alloys: Tejas Umale1; Ibrahim Karaman1; Anjana Talapatra1; Raymundo Arroyave1; Ruben Santamarta2; 1Texas A&M University; 2University de les Illes Balears
Ni-Ti-Hf HTSMAs are a potential candidate for thermo-mechanical actuators because of their high transformation temperature, superelasticity and good dimensional stability. The transformation characteristics are strongly dependent on chemistry and thermal processing owing to the formation of nano-dispersed H-phase precipitates, which controls the shape memory response of the material. In this work, we aim to understand the role of chemistry and thermal processing on the transformation characteristics of a wide range of compositions, varying nickel from Ni=49.8% to Ni=51% and hafnium from Hf=0% to Hf=30%. We found that transformation characteristics are very sensitive to nickel content for varying hafnium contents. We also studied the phase equilibria in Ni-Ti-Hf system at different temperatures, by constructing ternary phase isotherms with the help of diffusion multiple experiments. Knowledge of equilibrium phases at different temperatures aids in understanding the H-phase precipitate chemistry more clearly, which is important for developing predictive precipitate models.
Advanced Characterization Study of Thermo-Mechanically Processed High Temperature Shape Memory Wires: Nathan Ley1; Othmane Benafan2; Marcus Young1; 1University of North Texas; 2NASA Glenn Research Center
High temperature shape memory alloys (HTSMAs) are becoming of more interest to the automotive, defense, and aerospace industries due to the need for elevated actuation temperatures above 100 °C. The transformation temperatures of the material can be tuned with the addition of alloying elements such as Hf, Pt, Pd, or Zr. In this study two Ni-rich HTSMAs, NiTiZr20¬ ¬¬and NiTiHf20 (at%) were thermo-mechanically processed via hot rolling and wire drawing (<500 µm diameter). Characterization of the materials actuation temperature was performed via differential scanning calorimetry (DSC), while the microstructural evolution of the material was characterized through scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) as well as, transmission electron microscopy (TEM) equipped with EDS and selected area electron diffraction (SAED) Synchrotron radiation x-ray diffraction (SR-XRD) was performed to evaluate the number of phases, texture, and phase/strain evolution as a function of temperature.