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Lecture

In situ neutron diffraction analyzing stress-induced phase transformation and martensite elasticity in [001]-oriented CoNiGa shape memory alloy single crystals

Tuesday (15.05.2018)
16:15 - 16:40
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Recent studies on stress-induced martensitic transformations in single crystals under compressive loads in [001]- oriented as-grown Co-Ni-Ga high temperature shape memory alloys (HT-SMAs) demonstrated excellent pseudoelastic behavior and cyclic stability up to 8 % macroscopic strain reached at 1000 MPa [I.V. Kireeva, Yu. I. Chumlyakov, Z. V. Pobedennaya, I. V. Kretinina, E. Cesari, S. B. Kustov, C. Picornell, J. Pons, I. Karaman (2010):  Physics of Metals and Metallography, 110, 78-90]. A narrow stress hysteresis was related to mechanical twinning of L10 martensite at RT. Another important aspect is the absence of activation of the 〈001〉{110} slip system in the B2 austenite in this geometry. This leads to the suppression of plastic deformation. Eventually, this behavior makes Co–Ni–Ga HT-SMAs promising candidates for several industrial applications. In situ neutron diffraction experiments were carried out using a newly installed testing setup on Co-Ni-Ga single crystals in order to assess the evolution of martensite domain variants particularly in the martensite elastic regime. Thus, the current study focuses on the elastic and anelastic deformation mechanisms in the pseudoelastic regime far beyond the maximum theoretical transformation strains. It is shown that the (twinned) martensite phase is able to withstand about 5 % elastic strain beyond the pseudoelastic stress-strain plateau, which significantly increases the overall deformation capability of this alloy system.

Speaker:
Alexander Reul
LMU Munich
Additional Authors:
  • Christian Lauhoff
    Universität Kassel
  • Philipp Krooß
    Universität Kassel
  • M.J. Gutmann
    SIS Facility, Rutherford Appleton Laboratory
  • Peter M. Kadletz
    Ludwig-Maximilians-Universität München
  • Prof. Yuriy Ivanovich Chumlyakov
    Tomsk State University
  • Prof. Dr.-Ing. Thomas Niendorf
    Universität Kassel
  • Prof. Dr. Wolfgang W. Schmahl
    Ludwig-Maximilians-Universität München