Novel Shape Memory Alloys: Session 7
Program Organizers: Othmane Benafan, NASA Glenn Research Center
Friday 2:00 PM
July 14, 2017
Location: Hyatt Regency Chicago
Session Chair: Gregory Gerstein, Leibniz Universität Hannover
Developing New Shape Memory Alloys by Thin Film Combinatorial Materials Science and High-throughput Experimentation: Alfred Ludwig1; Peer Decker2; 1Ruhr-University Bochum; 2Ruhr-Universität Bochum
For the discovery and optimization of shape memory alloys (SMA: Ni-Ti-, Fe-, oxide-based) combinatorial and high-throughput thin film experimentation methods are applied. SMAs are deposited as thin film materials libraries by combinatorial sputtering. The obtained materials libraries are measured by high-throughput characterization methods in order to correlate compositional data with structural and functional properties. Results are visualized as composition-structure-function diagrams (functional phase diagrams). This contribution discusses key results which were obtained by this approach, involving the determination of complete composition ranges undergoing martensitic transformations in several SMAs as well as quantitative mapping of phase transformation properties in the identified composition ranges. SMAs with vanishing thermal hysteresis were discovered. Up-scaling from thin film to bulk is discussed as well as limitations of thin film SMA towards the nanoscale. Finally, the application of the combinatorial approach for high temperature SMA (Ti-Ta-X) and VO2-based SMA thin films is addressed.
Microstructures and Workability of (35.5-x)Ti-49.5Ni-15Hf-xNb Shape Memory Alloys: Sung-cheol Kim1; Tae-hyun Nam1; 1GyeongSang National University
Microstructures and workability of (35.5-x)Ti-49.5Ni-15Hf-xNb (x=0, 1.5, 3, 4.5, 6) (at.%) alloys were studied by means of scanning electron microscopy, x-ray diffraction, differential scanning calorimetry and tensile tests. (35.5-x)Ti-Ni-15Hf-xNb alloys with Nb content less than 4.5 at.% consisted of the B19′ martensite matrix, (Ti,Hf,Nb)2Ni and Nb-rich β phases, while a Ti-49.5Ni-15Hf alloy consisted of the B19’ martensite matrix and (Ti,Hf)2Ni phase. (35.5-x)Ti-Ni-15Hf-xNb alloys with Nb content more than 4.5 at.% consisted of the B19′ martensite matrix, (Ti,Hf,Nb)2Ni, Nb-rich β phases, Hf-rich phase. The fracture strain of (35.5-x)Ti-Ni-15Hf-xNb alloys increased from 4.0% to 18.2% with increasing Nb content from 0 at.% to 6 at.%, which was ascribed to the formation of a soft Nb-rich ß-phase. Ms(the B2-B19’ transformation start temperature) decreased from 477.4 K to 211.8 K with increasing Nb content from 0 at.% to 6 at.%. Solution treated (35.5-x)Ti-Ni-15Hf-xNb alloys showed partial superelasticity.
Simulation under Uncertainty for Non-Spherical Precipitation Behavior in Ni-Ti-Hf High Temperature Shape Memory Alloys: Pejman Honarmandi1; Raymundo Arroyave1; 1Texas A&M University
Ni-Ti-Hf alloys have recently been in the spotlight due to their remarkable high temperature actuation and their lower cost compared to other rival ternary systems. In addition, the capability of these alloys for nano-precipitation results in a high dimensional stability during cyclic actuations. Due to the importance of this effect, the non-spherical precipitation behavior of these alloys is simulated by considering a concurrent nucleation, growth, and coarsening phenomena based on a generalized Kampmann-Wagner Numerical (KWN) model. Model uncertainty analysis is also performed using an adaptive Markov Chain Monte Carlo-Metropolis Hastings algorithm in the framework of Bayes’ theorem. In this approach, sensitive model parameters are calibrated with available experimental results for model outputs by considering prior knowledge for parameters. Then, the plausible mean values and uncertainties of the obtained parameters are correlated to model outputs and their uncertainties through the propagation of uncertainty.
Processing and Functional Stability of Ti-Ta-based High Temperature Shape Memory Alloys: Alexander Paulsen1; Hannah Sommer1; Jorge Pelegrina2; Alejandro Yawny2; Christoph Somsen1; Jan Frenzel1; Gunther Eggeler1; 1Ruhr-Universitaet Bochum; 2Centro Atómico Bariloche
Ti-Ta shape memory alloys (SMAs) are attractive for applications as high temperature SMAs due to their high MS temperatures and excellent workability. We provide results on processing and functional stability of Ti-Ta SMAs. We show how high quality Ti-Ta alloys can be produced through arc melting and subsequent thermal and thermomechanical treatments. The functional stability of Ti-Ta was evaluated through cyclic differential scanning calorimetry (DSC), heat treatments, resistivity measurements and microstructural analysis involving electron microscopy and synchrotron diffraction. It is documented that binary Ti-Ta only exhibits a relatively poor stability due to the formation of omega phase at relatively low temperatures. In the present work we present time temperature transformation diagrams for Ti-30Ta and Ti-30Ta-3Al. We show that Al alloy additions slow down the kinetics of omega phase precipitation and thus provide a more stable transformation behavior.
Functional Degradation in Novel High-temperature Shape Memory Alloys: Philipp Krooß1; Malte Vollmer1; Peter Kadletz2; Christoph Somsen3; Hans Jürgen Maier4; Thomas Niendorf1; 1University of Kassel; 2Ludwig-Maximilians-Universität; 3Ruhr-Universität Bochum; 4Leibniz Universität Hannover
Conventional SMAs, such as Ni-Ti alloys, often lose their functional properties at about 100 °C and/or are high in processing costs. To overcome current limitations and widen the field of applications, novel alloy systems, i.e. high-temperature (HT-) SMAs, have been developed recently. HT-SMAs, such as Ni Ti X (X=Pd,Pt,Zr,Hf), Ti-Ta-Al and Co-Ni-Ga show good functional properties at elevated temperatures. Cyclic stability of these alloys is crucial for an intended industrial application. However, data reporting on functional degradation are rare. In order to close this gap, the current study discusses elementary mechanisms responsible for degradation of functional properties. Using different in situ techniques the functional and structural cyclic material response was characterized for novel SMAs, such as Ti-Ta-Al and Co-Ni-Ga. Detailed microstructure analyses were performed using electron-microscopy, optical microscopy and neutron diffraction revealing microstructural evolution upon cycling.
3:30 PM Break