Novel Shape Memory Alloys: Session 1
Program Organizers: Othmane Benafan, NASA Glenn Research Center

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

Session Chair: Othmane Benafan, NASA Glenn Research Center

2:00 PM  Invited
Fe-based Shape Memory Alloys: Hidden Potential and Challenges: Ibrahim Karaman1; Hande Ozcan1; Ji Ma1; 1Texas A&M University
    Fe-based shape memory alloys (SMAs) show great potential as low-cost superelastic materials for use in practical applications as they provide high theoretical transformation strain, high strength and exhibit a unique temperature invariant stress induced martensitic transformation (SIM). Additionally, these alloys exhibit stress-, strain- and temperature- induced magnetization changes which are beyond the capabilities of NiTi SMAs. Due to these unique properties Fe-based SMAs are strong candidates for applications which cannot be served by conventional SMAs, such as solid-state sensing and energy harvesting. In this study, the recent developments and current challenges in novel Fe-based SMAs; FeNiCoAl(Ta, Nb, Ti), FeMnAlNi and FeMnAlNiTi are presented. The basic mechanisms of the thermoelastic martensitic transformation, grain growth, and the effects of nano precipitation and Ti addition on superelastic properties will be discussed. Finally, the unsolved scientific issues for future research will be presented.

2:40 PM  
Effect of Temperature and Crystallographic Orientation on Superelastic Strain of FeNiCoAlTaB Single Crystals: Robert Chulist1; Tomasz Tokarski2; Grzegorz Cios3; Yuri Chumlyakov4; 1Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 30-059 Krakow, Poland; 2AGH University of Science and Technology, Academic Centre for Materials and nanotechnology, Mickiewicza 30, 30-059 Krakow, Poland ; 3AGH University of Science and Technology, Academic Centre for Materials and nanotechnology, Mickiewicza 30, 30-059 Krakow, Poland; 4Tomsk State University, Siberian Physical Technical Institute, Tomsk 634050, Russia
    Fe-based alloys (Fe-28Ni-17Co-11.5Al-0.5Ta-0.5B abbreviated NCATB) belong to the quite new family of shape memory alloys showing a large superelastic strain at room temperature. However, significant strain differences between single and polycrystals are observed. Therefore, to provide new information on the mechanism of superelasticity observed in NCATB alloys single crystals with (100), (110) and (111) orientations were compressed at different temperatures (273, 123, and 77 K). Elastic, plastic or elasto-plastic response are observed depending on the orientation and deformation temperature. The global and local orientation measurements are determined by diffraction of high-energy synchrotron radiation and electron backscatter diffraction, respectively. The results are discussed with respect to crystallographic orientation, deformation mode, precipitations and phase transformations.

3:00 PM  
Effect of Nano-precipitates on Stress Induced Martensitic Transformation in Polycrystalline FeMnAlNi Superelastic Wires: Hande Ozcan1; Ji Ma1; Ruben Santamarta2; Ronald Noebe3; Yury Chumlyakov4; Ibrahim Karaman1; 1Texas A&M University; 2Universitat de les Illes Balears; 3NASA Glenn Research Center; 4Tomsk State University
    In this study, we showed the effect of nano-precipitates on the stress induced martensitic transformation (SIM) behavior and superelasticity in Fe43.5Mn34Al15Ni7.5 polycrystalline wires, by changing the precipitate sizes from 1 nm to 10 nm. We observed that having bamboo structured grains with a large grain size to diameter ratio is a necessary condition for obtaining perfect superelasticity. In the wires aged at 200C, tunable transformation stress levels as high as 600 MPa without loss of recoverable superelastic strain (6.7%) are obtained by changing the size and volume fraction of nano-precipitates. Additionally, this study shows for the first time that FeMnAlNi shape memory alloys can be aged at room temperature, growing the precipitate seeds, that formed during quenching from the high temperature, into a few nanometer size particles, resulting in superelasticity. Room temperature aging must be taken into account as an important factor in applications requiring long term stability.

3:15 PM  
Transformation Stress Modeling in New Fe-Mn-Al-Ni Shape Memory Alloy: Avinesh Ojha1; Huseyin Sehitoglu1; 1University of Illinois-Urbana Champaign
    We investigate the bcc-fcc transformation in the new shape memory alloy FeMnAlNi utilizing density functional theory calculations for double shear. We formulate an energy expression to derive the fcc martensite formation stress, incorporating the transformation shear energy and the elastic interactions of the dislocations. The critical bcc-fcc transformation stress was determined as 191 MPa, which is close to the experiments. Concurrently, we also establish the fcc twinning and slip stresses as 201 MPa and 335 MPa respectively. The higher slip resistance ensures recoverability of the transformation. We observe that the Bogers-Burgers double shear mechanism proceeds with a much lower energy barrier and is favored over the ‘classical’ Bain deformation. Overall, the parameters obtained from DFT calculations are devoid of any empiricism and the prediction of these critical stresses permit the design of new iron based SMAs.

3:30 PM Break