Novel Functional Behaviors: Beyond Shape Memory Effect & Superelasticity: Session 5
Program Organizers: Ibrahim Karaman, Texas A&M University

Friday 10:20 AM
July 14, 2017
Room: Water Tower
Location: Hyatt Regency Chicago

Session Chair: Enke Liu, Institute of Physics, Chinese Academy of Sciences

10:20 AM  Invited
Tailored Thermal Expansion Alloys: James Monroe1; Ibrahim Karaman2; 1Thermal Expansion Solutions/Texas A&M; 2Texas A&M University
    The unique thermal expansion anisotropy exhibited by the thermo-elastic martensite in shape memory alloys is the heart of tailored thermal expansion. This relatively recent discovery could enable new solutions to long-standing thermal expansion and compensation problems found in the aerospace, manufacturing, optics, oil and gas, and automotive industries. While a good foundation of research has been performed to characterize this phenomenon, many questions remain about the origin and mechanism of the thermal expansion anisotropy. In this talk, we will explore the current understanding of tailored thermal expansion alloys and discuss their future.

11:00 AM  
Reversible negative thermal expansion response and phase transformation behavior of a Ti-rich Ti54Ni46 alloy prepared by rapid solidification: Zhong-Xun Zhao1; Xing Zhu1; Xiao Ma1; Shan-Shan Cao1; Chang-Bo Ke1; Xin-Ping Zhang1; 1South China University of Technology
    Ti-rich Ti-Ni alloys are unique metallic materials which possess the reversible negative thermal expansion (NTE) property. Rapidly solidified fine-grained Ti-46.0 at.% Ni alloys were prepared by vacuum arc melting followed by vacuum suction casting. Phase transformation and thermal expansion characteristics under stress-free thermal cycling were investigated by using differential scanning calorimetry (DSC) and thermomechanical analyzer (TMA) between 253 K and 423 K at heating/cooling rates of 10 K/min and 3 K/min respectively. The results manifest that both the martensite start temperature Ms and NTE start temperature CNs drop rapidly during the initial 20 cycles then decrease slowly, and tend to be relatively unchanged after about 30 thermal cycles. Notably, Ms shifts from 336 K to 324 K and CNs reduces from 339 K to 321 K after 50 thermal cycles. Moreover, in contrast to the cases of Ni-rich Ti-Ni alloys, no R-phase transformation is detected during the thermal cycling.

11:20 AM  
Tailorable Thermal Expansion in Beta-Titanium Alloys: Dominic Gehring1; James Monroe1; Ibrahim Karaman1; 1Texas A&M University
    Recent studies in shape memory alloys such as NiTi, NiTiPd, CoNiGa, and TiNb have demonstrated anomalous anisotropic thermal expansion in lower-symmetry martensites. The combination of unit cell level thermal expansion anisotropy and crystallographic texturing has been shown to yield tailorable directional/planar thermal expansion, including the negative, suited for precision applications in electronic, optical, and aerospace systems. Here, the behavior of TiNb alloys with orthorhombic martensite was characterized after texturing via cold rolling up to 80% reduction. In this system increased Nb content yielded larger thermal expansion anisotropy and simultaneous strengthening crystallographic texture allowed the largest observed negative and positive thermal expansion. This ranged between -30 and +30 ppm/K bulk thermal expansion along principal directions. Mechanisms behind unexpected characteristics in TiNb such as non-linear thermal expansion response are yet to be fully understood but this system provides a prototype for characteristics common to tailorable CTE materials and appear consistent with NiTi.

11:35 AM  
Integrated Multiphysical SMA Actuation Using Embedded Liquid Metal Circuits: Jacob Mingear1; Brent Bielefeldt1; Darren Hartl1; 1Texas A&M University
    Shape memory alloy-based actuators are thermally driven and limited in the frequency of their cyclic actuation responses. In this research effort, liquid metal (LM) has been investigated as an electrically conductive heat transfer fluid in the context of multiphysical SMA-actuators. Gallium-indium-tin eutectic liquid is introduced into complex actuator geometries via internal channels. Flow of the liquid metal is effective in rapidly cooling SMA actuators. Thermo-electro-magnetic modeling has also shown that appropriately configured LM channels are effective in inductively heating the bulk SMA. This research demonstrates an inductively heated and fluid-cooled SMA actuator for which LM comprises both the electrical and fluid circuits. To address the critical issue of LM-induced corrosion, focused studies have show that NiTi is unaffected by this phenomenon, including in situations in which SMA bodies are undergoing cyclic transformation between martensite and austenite.

11:55 AM Break