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H J Maier - One of the best experts on this subject based on the ideXlab platform.

  • direct microstructure design by hot extrusion high temperature Shape Memory Alloys with bamboo like microstructure
    Scripta Materialia, 2019
    Co-Authors: Thomas Niendorf, P Kroos, C Lauhoff, Elvira Karsten, Gregory Gerstein, A Liehr, H J Maier
    Abstract:

    Abstract High-temperature Shape Memory Alloys are promising candidates for actuation/damping applications at elevated temperatures. To account for pronounced instabilities at elevated temperatures of conventional Alloys, novel alloy systems have been developed to address this issue. Yet, most systems suffer from high costs/limited formability. Bamboo-like microstructures have proven to provide for a suitable microstructural condition for superior performance in numerous Alloys, however, robust processing of promising high-temperature Shape Memory Alloys is challenging. The current study reports on a novel thermo-mechanical processing route allowing robust processing of hard to form Co-Ni-Ga Shape Memory Alloys. This will assist to overcome a major roadblock towards widespread use of these materials.

  • martensite aging avenue to new high temperature Shape Memory Alloys
    Acta Materialia, 2015
    Co-Authors: Thomas Niendorf, P Kroos, Christoph Somsen, G Eggeler, Yuri Chumlyakov, H J Maier
    Abstract:

    Abstract High-temperature Shape Memory Alloys are attractive for efficient solid state actuation. A key criterion for Shape Memory Alloys is the martensite start temperature. The current study introduces a concept for increasing this temperature of Alloys initially not suited for high-temperature actuation. Aging of stress-induced martensite, referred to as SIM-aging in the current work, is able to increase the martensite start temperature by about 130 °C as demonstrated in the present study for a Co–Ni–Ga Shape Memory alloy. The increase of transformation temperatures can be explained based on the concept of symmetry-conforming short-range order. Following SIM-aging the Co–Ni–Ga alloy shows cyclic actuation stability at elevated temperatures. While martensite aging has always been viewed as detrimental in the past, it can actually be exploited to design new classes of high-temperature Shape Memory Alloys with excellent properties.

W Zhang - One of the best experts on this subject based on the ideXlab platform.

  • a micromechanical model for polycrystalline Shape Memory Alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004
    Co-Authors: Klaus Hackl, Martin Schmidtbaldassari, W Zhang
    Abstract:

    We develop an energy-based model for polycrystalline Shape-Memory Alloys which allows to predict all relevant features such as pseudoelasticity and the Shape-Memory effect. The theory is based on orientation-distribution of martensite-variants and the minimization of total elastic strain energy and dissipation due to phase-transformation. Applications in a two-dimensional context are given.

G Eggeler - One of the best experts on this subject based on the ideXlab platform.

  • martensite aging avenue to new high temperature Shape Memory Alloys
    Acta Materialia, 2015
    Co-Authors: Thomas Niendorf, P Kroos, Christoph Somsen, G Eggeler, Yuri Chumlyakov, H J Maier
    Abstract:

    Abstract High-temperature Shape Memory Alloys are attractive for efficient solid state actuation. A key criterion for Shape Memory Alloys is the martensite start temperature. The current study introduces a concept for increasing this temperature of Alloys initially not suited for high-temperature actuation. Aging of stress-induced martensite, referred to as SIM-aging in the current work, is able to increase the martensite start temperature by about 130 °C as demonstrated in the present study for a Co–Ni–Ga Shape Memory alloy. The increase of transformation temperatures can be explained based on the concept of symmetry-conforming short-range order. Following SIM-aging the Co–Ni–Ga alloy shows cyclic actuation stability at elevated temperatures. While martensite aging has always been viewed as detrimental in the past, it can actually be exploited to design new classes of high-temperature Shape Memory Alloys with excellent properties.

  • structural and functional fatigue of niti Shape Memory Alloys
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004
    Co-Authors: G Eggeler, Erhard Hornbogen, A Yawny, A Heckmann, Martin F X Wagner
    Abstract:

    Abstract Cyclic loading is one of the generic characteristic features of many of the present and potential future applications of NiTi Shape Memory Alloys, no matter whether they exploit mechanical (pseudo-elasticity) or thermal Shape Memory (one and two way effect). Cyclic loading may well be associated with structural and functional fatigue, which both limit the service life of Shape Memory components. By “structural fatigue” we mean the microstructural damage that accumulates during cyclic loading and eventually leads to fatigue failure. There is a need to understand how microstructures can be optimized to provide good fatigue resistance. The term “functional fatigue” indicates that Shape Memory effects like the working displacement in a one way effect (1WE) actuator or the dissipated energy in a loading–unloading cycle of a pseudo-elastic (PE) damping application decrease with increasing cycle numbers. This is also due to a gradual change in microstructure. In both cases it is important to know how fatigue cycling affects Shape Memory properties. The present paper considers structural and functional fatigue of NiTi Shape Memory Alloys. It discusses four cases of fatigue in NiTi Shape Memory Alloys: (1) The evolution of the stress–strain hysteresis in low cycle pull–pull fatigue of pseudo-elastic NiTi wires. (2) Bending–rotation fatigue rupture of pseudo-elastic NiTi wires. (3) Strain localization during the stress induced formation of martensite. (4) Generic features of functional fatigue in NiTi Shape Memory actuator springs. The paper shows that fatigue of Shape Memory Alloys is a fascinating research field and highlights the need for further work in this area.

Thomas Niendorf - One of the best experts on this subject based on the ideXlab platform.

  • direct microstructure design by hot extrusion high temperature Shape Memory Alloys with bamboo like microstructure
    Scripta Materialia, 2019
    Co-Authors: Thomas Niendorf, P Kroos, C Lauhoff, Elvira Karsten, Gregory Gerstein, A Liehr, H J Maier
    Abstract:

    Abstract High-temperature Shape Memory Alloys are promising candidates for actuation/damping applications at elevated temperatures. To account for pronounced instabilities at elevated temperatures of conventional Alloys, novel alloy systems have been developed to address this issue. Yet, most systems suffer from high costs/limited formability. Bamboo-like microstructures have proven to provide for a suitable microstructural condition for superior performance in numerous Alloys, however, robust processing of promising high-temperature Shape Memory Alloys is challenging. The current study reports on a novel thermo-mechanical processing route allowing robust processing of hard to form Co-Ni-Ga Shape Memory Alloys. This will assist to overcome a major roadblock towards widespread use of these materials.

  • martensite aging avenue to new high temperature Shape Memory Alloys
    Acta Materialia, 2015
    Co-Authors: Thomas Niendorf, P Kroos, Christoph Somsen, G Eggeler, Yuri Chumlyakov, H J Maier
    Abstract:

    Abstract High-temperature Shape Memory Alloys are attractive for efficient solid state actuation. A key criterion for Shape Memory Alloys is the martensite start temperature. The current study introduces a concept for increasing this temperature of Alloys initially not suited for high-temperature actuation. Aging of stress-induced martensite, referred to as SIM-aging in the current work, is able to increase the martensite start temperature by about 130 °C as demonstrated in the present study for a Co–Ni–Ga Shape Memory alloy. The increase of transformation temperatures can be explained based on the concept of symmetry-conforming short-range order. Following SIM-aging the Co–Ni–Ga alloy shows cyclic actuation stability at elevated temperatures. While martensite aging has always been viewed as detrimental in the past, it can actually be exploited to design new classes of high-temperature Shape Memory Alloys with excellent properties.

D Canadinc - One of the best experts on this subject based on the ideXlab platform.

  • ultra high temperature multi component Shape Memory Alloys
    Scripta Materialia, 2019
    Co-Authors: D Canadinc, William Trehern, I Karaman, Fanping Sun, Zaffir Chaudhry
    Abstract:

    Abstract This paper presents martensitic transformation characteristics of selected multi-component (Ni,Pd) 50 (Ti,Hf,Zr) 50 Alloys, with an emphasis on superelasticity and thermal actuation behavior. We report, for the first time, austenite finish temperatures beyond 700 °C in NiTi-based high temperature Shape Memory Alloys without the presence of platinum and gold. The increase in transformation temperatures, and transformation stress and recovered strains at elevated temperatures are attributed to the high configurational entropy of the studied Alloys. Based on the current findings, we introduce multi-component ultra-high temperature Shape Memory Alloys, which are expected to pioneer a completely new field of study and applications for Shape Memory Alloys.