Martensite stabilization in shape memory alloys – Experimental evidence for short-range ordering

Effect of Stress-Induced Martensite Stabilization on Acoustic Emission Characteristics and the Entropy of Martensitic Transformation in Shape Memory Ni51Fe18Ga27Co4 Single Crystal

“…It is known that martensite stabilization heat treatments, under uniaxial stress, large enough to produce a single variant martensite in shape memory alloys, by aging at temperatures allowing atomic diffusion (stress-induced martensite stabilization, SIM) result in stabilization of the martensite [1][2][3][4][5][6][7][8][9][10][11][12]. While this stabilization, which can be understood on the basis of the so-called symmetry conforming short-range ordering process [5,13,14], plausibly causes a shift of transformation temperatures to higher values, significant improvement of the shape memory functional properties was also achieved [1][2][3][4][5][6][7][8][9][10][11][12]. For instance, it was demonstrated in [1] that martensite aging offers a general concept for the production of high temperature actuator materials, and the authors of [1] introduced a new class of high-temperature ferromagnetic shape memory alloys by choosing Co 49 Ni 21 Ga 30 alloy as a model material.…”

“…Co 4 single crystal, and similar results were published, e.g., on NiMnGa [9] and Co 49 Ni 21 Ga 30 [15] and CoNiAl [8] alloys. Thus, in order to reach high-deformation strains (close to the theoretical limits), due to the shift of the transformation temperatures to higher values and the stabilization of the two-way shape memory properties, high-temperature, high-strength ferromagnetic shape memory alloys were developed [1,4,5,8,9]. In a very recent paper [10], it was shown that in Ni 51 Fe 18 Ga 27 Co 4 single crystal not only a two-way shape memory behaviour (with a reversible tensile strain of 9%) was achieved by SIM-aging but giant rubber-like behaviour was also observed up to 15%, during reorientation of martensite variants.…”

Investigation of TiNi shape memory alloy for thermosensitive wire drive

“…Stressstrain curves during active deformation in the martensitic state up to 15% of residual strain and the shape memory There is a significant shift of the characteristic temperatures of the reverse martensitic transformation after active straining in the martensitic state due to the well-known effect of martensite stabilisation [8][9][10][11][12][13]. This fact does not allow us to use this method for preparing the wire drive with the desired operation temperature range.…”

Cyclic Degradation of Co49Ni21Ga30 High-Temperature Shape Memory Alloy: On the Roles of Dislocation Activity and Chemical Order

“…Processing of polycrystalline Co-Ni-Ga materials can be significantly improved by the precipitation of the disordered secondary c-phase (A1), which makes the alloy distinctly better workable than its counterpart, Co-Ni-Al [18]. In general, Co-Ni-Ga SMAs are characterized by a thermoelastic martensitic transformation from a high-temperature cubic B2-ordered parent phase to a tetragonal low-temperature martensitic phase with an L1 0 structure [31]. Co-Ni-Ga HT-SMAs have been intensively investigated in recent years [15-17, 19-22, 29-31].…”

“…The increase of transformation temperatures was explained based on a change of the Gibbs free energy due to a change of chemical order, which was, among others, explained by the principle of symmetry-conforming, short-range ordering (SC-SRO), proposed by Ren and Otsuka [32]. Neutron diffraction analysis was employed for experimental determination of underlying mechanisms [31]. Differing intensities of superlattice reflections were found and attributed to changes in chemical order.…”