Engineering Applications and Devices: Session 1
Program Organizers: Alan Pelton, G.RAU Inc.

Monday 2:00 PM
July 10, 2017
Room: Wrigley
Location: Hyatt Regency Chicago

Session Chair: Alan Pelton, G.RAU Inc.

2:00 PM  Invited
Ultra-low Fatigue of NiTiCu-based Shape Memory Thin Films: Eckhard Quandt1; Christoph Chluba1; Jake Steiner2; Wenwei Ge2; Manfred Wuttig2; 1University of Kiel; 2University of Maryland
    Functional shape memory alloys need to operate reversibly and repeatedly. This is especially crucial for many future applications such as artificial heart valves or elastocaloric cooling, where more than ten million transformation cycles will be required. Here we report on the discovery of an ultra-low fatigue shape memory alloy film system based on TiNiCu that allows at least ten million transformation cycles. We found these films contain Ti2Cu precipitates embedded in the base alloy that serve as sentinels to ensure complete and reproducible transformation in the course of each memory cycle (1). Using stress dependent in situ synchrotron investigations the change of lattice constants of B2 phase and stress induced B19 phase during the superelastic transformation can be quantified. This measurement enables the compatibility calculation of austenite and martensite phases which is known to have a strong influence on the superelastic hysteresis and the thermally induced transformation stability. The microstructural influences of grain size, precipitates and crystallographic compatibility on the functional degradation of NiTiCu-based thin films will be discussed.

2:40 PM  
Evolution of Macroscopic Elastic Moduli of Martensitic Polycrystalline NiTi and NiTiCu Shape Memory Alloys with Pseudoplastic Straining: Petr Sedlak1; Hanus Seiner1; Miroslav Frost1; Michal Landa1; Martina Thomasova2; Petr Sittner3; 1Institute of Thermomechanics CAS; 2Faculty of Nuclear Sciences and Physical Engineering, CTU in Prague; 3Institute of Physics, CAS
    Several studies of strong elastic anisotropy of single crystals of both austenitic and martensitic phases of shape memory alloys have been reported in literature, but for theoretical and practical reasons it is also interesting to examine elasticity of polycrystalline samples used more frequently in SMA applications. In this contribution, elastic constants of polycrystalline NiTi and NiTiCu alloys in the martensite phase were determined by resonant ultrasound spectroscopy and the evolution of these constants was studied with subsequent applications of compressive loads inducing reorientation of martensitic variants. Results show that in comparison to weak elastic anisotropy of polycrystalline austenite given by sample texture and weak anisotropy of temperature induced martensite, the anisotropy of stress-oriented martensite is huge and comparable to large anisotropy of martensite single crystals. A qualitative difference in behaviors was observed between the monoclinic B19' martensite in the NiTi alloy and the orthorhombic B19 martensite in the NiTiCu alloy.

3:00 PM  
Measurement of the Growth Rate of Martensite Plates using Spontaneous Magnetic Emission Peaks (SME): Edgar Apaza Huallpa1; Julio Antonio Capó Sánchez2; Hélio Goldenstein1; 1Universidade de São Paulo; 2Universidad de Oriente
     The spontaneous magnetic emission (SME) [1-3], a recently described phenomenon, which already showed to be a promising tool to monitor the martensitic transformation, is used in this work to determine the growth rate of martensite plates in a Fe-Ni-C alloy. The duration (time length) of individual magnetic peaks emitted at the start (near Ms) and at the end (Mf) of the martensitic transformation during continuous cooling experiments were measured and compared with the average lengths of the first (at Ms) and last plates (at Mf), obtained using quantitative metallography. The SME, a phenomenon more sensitive than other global measurements like resistivity [3], dilatometry, etc., does not require a critical volume of transformation in order to be detected; as a consequence the SME is able to detect signals emitted by individual growing plates. <br>Keywords: SME, Fe-Ni-C, Growth rate of individual plates, Ms, Mf <br>[1] <br>[2]<br>[3]

3:15 PM  
Functional Fatigue Behavior of NiTi SMA Artificial Anal Sphincter During Long-Term Thermal Cycling : Yuanyuan Li1; Caiyou Zeng1; Shanshan Cao1; Xiao Ma1; Xin-ping Zhang1; 1South China University of Technology
    Rapidly solidified (RS) and constraint-aged NiTi alloy was prepared to make artificial anal sphincter (AAS) aiming at solving fecal incontinence. The AAS consists of two NiTi strips and performs “open” and “close” function on heating and cooling. For high reliability requirement, the alloy has to perform sufficient two-way shape memory effect (TWSME) in 308~328 K during long-term thermal cycling. Phase transformation behavior, recovery ratio and microstructure were characterized by DSC, photography and TEM. Results show that deformability of AAS barely decays in 308~328 K after 30000 thermal cycles, identified with stable phase transformation behavior and TWSME. Meanwhile, oriented Ni4Ti3 in matrix of B2, R-phase and martensite has stable size of 100~150 nm. No new phase or obvious defect exists. Actually, fine grained microstructure of RS NiTi alloy contributes to excellent stability through restricting the growth of Ni4Ti3 and defects. However, for thermo-mechanical cycling with external stress, AAS fatigues in advance.

3:30 PM Break