Novel Functional Behaviors: Beyond Shape Memory Effect & Superelasticity: Session 4
Program Organizers: Ibrahim Karaman, Texas A&M University

Friday 8:00 AM
July 14, 2017
Room: Water Tower
Location: Hyatt Regency Chicago

Session Chair: Ibrahim Karaman, Texas A&M University

8:00 AM  
Martensitic Transformation of Ni-Mn-X Heusler Alloys with X = Ga, In and Sn: Peter Entel1; Ibrahim Karaman1; Raymundo Arroyave1; Mehmet Acet1; Markus Gruner1; 1University of Duisburg-Essen
     The martensitic transformation of rapidly and less rapidly cooled Heusler alloys of type Ni-Mn-X with X = Ga, In and Sn is investigated by ab initio calculations and Monte Carlo simulationns For the rapidly cooled alloys weobtain the functional magnetocaloric properties near the magnetocaloric transiton. For the less rapidly quenched alloy these properties start to change and vanish in case of very slow cooling. This is an important effect which shows that none of the Heusler alloys is in thermal equilibrium but instead the alloy transfroms during temper-annealing into a dual-phase composite alloy, the two phases are identified to be cubic Ni-Mn-X and tetragonal NiMn. In addition, we discuss kinetic arrestphenomena of the rapidly quenched alloys.

8:20 AM  
Temperature Induced Successive Martensitic and Inter-martensitic Phase Transformations of Ni2.16Mn0.84Ga Heusler Alloy: Pnina Ari-Gur1; Amila Madiligama1; Yang Ren2; Vladimir Shavrov3; Victor Koledov3; Yangling Ge4; James George1; 1Western Michigan University; 2Argonne National Laboratory; 3Russian Academy of Science; 4Aalto University
    The Curie and martensitic transformation temperatures merge in Ni2+XMn1-XGa Heusler alloys when x is around 0.2. These merged magneto-structural transformations make them attractive in many technological applications. One such alloy, Ni2.16Mn0.84Ga, had shown a great potential as a magnetocaloric material (ΔQ = 4900 J/kg at 343 K under H = 140 kOe). In this study, the crystalline structures and phase transformations of this alloy were analyzed using Rietveld refinements of synchrotron diffraction data collected at Argonne National Laboratory. The alloy undergoes temperature-induced inter-martensitic and martensitic phase transformations upon heating around 282.0 K and 332.0 K, respectively. The austenic structure is cubic L21 (Fm3 ̅m); upon cooling it transforms into martensite, monoclinic 7M modulated structure (P 1 2/m 1). This phase is stable in a narrow temperature range and upon further cooling it transforms into a non-modulated tetragonal L10 structure (I 4⁄m m m).

8:40 AM  
EBSD Study of the Branched Needle Microstructure in Ni-Mn-Ga 10M Martensite: Robert Chulist1; Ladislav Straka2; Alexei Sozinov3; Tomasz Tokarski4; Werner Skrotzki5; 1Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 30-059 Krakow, Poland; 2Institute of Physics ASCR, Na Slovance 2, 182 21 Praha 8, Czech Republic; 3Material Physics Laboratory, Lappeenranta University of Technology, Laitaatsillantie 3, 57170 Savonlinna, Finland; 4AGH University of Science and Technology, Academic Centre for Materials and Nanotechnology, Mickiewicza 30, 30-059 Krakow, Poland; 5Institut für Strukturphysik, Technische Universität Dresden, D-01062 Dresden, Germany
     Cross-configuration of conjugate twin boundaries and their interaction under an applied stress in NiMnGa 10M martensite was studied using electron backscatter diffraction in the scanning electron microscopy. The initial microstructure consists of two twin boundaries of triangle shape. Compression and unloading of such a configuration results in a recoverable strain. As deformation proceeds thin branched needles with type I twin boundaries inside the central domain are created while some type II twin boundaries can be predominantly detected outside the triangle domain. Using orientation analysis a mechanism of twin annihilation based on the rigid body rotation is proposed. The financial support by the Ministry of Science and Higher Education of Poland within the Project No. 0063/IP2/2015/73 and Homing Plus Project of Foundation for Polish Science, co-financed from European Union, Regional Development Fund are acknowledged.

9:00 AM  
Tuning the Magnetocaloric Effect in Melt-extracted Ni-Mn-Ga Microwires: Mingfang Qian1; Xuexi Zhang1; Longsha Wei1; Jianfei Sun1; Lin Geng1; Hua-Xin Peng2; 1Harbin Institute of Technology; 2Zhejiang University
    We present that giant MCE can be achieved in annealed Ni50.4Mn29.4Ga20.2 microwires by merging the first-order and second-order transitions where a strong magneto-structural coupling was existed. An absolute maximum value of the isothermal magnetic entropy change of 24.9 J/kg K was achieved at the magnetic field change of 50000 Oe, being comparable to or even superior to that of polycrystalline bulk alloys. While a real magnetic refrigerator requires not only a large MCE but also a wide temperature span of the MCE. For this purpose, partial magneto-structural coupling was required. Microwires with a first and second-order transition temperature difference of ~30K was designed and an intentional stepwise Mn-vaporizing annealing was applied in Ni50.6Mn28.1Ga21.3 microwires. It yielded a full width at half maximum (δFWHM) of ~60K from 330 to 390K and a refrigeration capacity (RC) as large as 240 J/Kg at 50000 Oe, which significantly improved the practicability of Ni-Mn-Ga alloys.

9:20 AM Break