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Subject: elasticity × WGL Institute: IFWD ×

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    Promoting abnormal grain growth in Fe-based shape memory alloys through compositional adjustments
    (London : Nature Publishing Group, 2019) Vollmer, M.; Arold, T.; Kriegel, M.J.; Klemm, V.; Degener, S.; Freudenberger, J.; Niendorf, T.
    Iron-based shape memory alloys are promising candidates for large-scale structural applications due to their cost efficiency and the possibility of using conventional processing routes from the steel industry. However, recently developed alloy systems like Fe–Mn–Al–Ni suffer from low recoverability if the grains do not completely cover the sample cross-section. To overcome this issue, here we show that small amounts of titanium added to Fe–Mn–Al–Ni significantly enhance abnormal grain growth due to a considerable refinement of the subgrain sizes, whereas small amounts of chromium lead to a strong inhibition of abnormal grain growth. By tailoring and promoting abnormal grain growth it is possible to obtain very large single crystalline bars. We expect that the findings of the present study regarding the elementary mechanisms of abnormal grain growth and the role of chemical composition can be applied to tailor other alloy systems with similar microstructural features.
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    Two types of magnetic shape-memory effects from twinned microstructure and magneto-structural coupling in Fe1 +yTe
    (Washington : National Academy of Sciences, 2019) Rößler, S.; Koz, C.; Wang, Z.; Skourski, Y.; Doerr, M.; Kasinathan, D.; Rosner, H.; Schmidt, M.; Schwarz, U.; Rößler, U.K.; Wirth, S.
    A detailed experimental investigation of Fe1+yTe (y = 0.11, 0.12) using pulsed magnetic fields up to 60 T confirms remarkable magnetic shape-memory (MSM) effects. These effects result from magnetoelastic transformation processes in the low-temperature antiferromagnetic state of these materials. The observation of modulated and finely twinned microstructure at the nanoscale through scanning tunneling microscopy establishes a behavior similar to that of thermoelastic martensite. We identified the observed, elegant hierarchical twinning pattern of monoclinic crystallographic domains as an ideal realization of crossing twin bands. The antiferromagnetism of the monoclinic ground state allows for a magnetic-field–induced reorientation of these twin variants by the motion of one type of twin boundaries. At sufficiently high magnetic fields, we observed a second isothermal transformation process with large hysteresis for different directions of applied field. This gives rise to a second MSM effect caused by a phase transition back to the field-polarized tetragonal lattice state.