The mechanism of orientation dependence of cyclic stability of superelesticity in NiFeGaCo single crystals under compression
EE Timofeeva, EY Panchenko, NG Vetoshkina… - Russian Physics …, 2016 - Springer
EE Timofeeva, EY Panchenko, NG Vetoshkina, YI Chumlyakov, AI Tagiltsev, AS Eftifeeva…
Russian Physics Journal, 2016•SpringerUsing single crystals of the Ni 49 Fe 18 Ga 27 Co 6 (at.%) alloy, oriented along [001]-and
[123]-directions, cyclic stability of superelasticity is investigated in isothermal
loading/unloading cycles at T= A f+(12–15) K (100 cycles) under compressive stress as a
function of given strain per cycle, presence of disperse γ-phase particles measuring 5–10
μm, austenitic (B2 or L2 1) and stress-induced martensitic crystal structure (14M or L10). It is
shown that single-phase L2 1-crystals demonstrate high cyclic stability during L21–14M …
[123]-directions, cyclic stability of superelasticity is investigated in isothermal
loading/unloading cycles at T= A f+(12–15) K (100 cycles) under compressive stress as a
function of given strain per cycle, presence of disperse γ-phase particles measuring 5–10
μm, austenitic (B2 or L2 1) and stress-induced martensitic crystal structure (14M or L10). It is
shown that single-phase L2 1-crystals demonstrate high cyclic stability during L21–14M …
Using single crystals of the Ni49Fe18Ga27Co6 (at.%) alloy, oriented along [001]- and [123]-directions, cyclic stability of superelasticity is investigated in isothermal loading/unloading cycles at T = Af +(12–15) K (100 cycles) under compressive stress as a function of given strain per cycle, presence of disperse γ-phase particles measuring 5–10 μm, austenitic (B2 or L21) and stress-induced martensitic crystal structure (14M or L10). It is shown that single-phase L21-crystals demonstrate high cyclic stability during L21–14M-transitions with narrow hysteresises Δσ < 50 MPa in the absence of detwinning of the martensite. During the development of L21–14M stress-induced transformation, the reversible energy ΔGrev for these crystals exceeds the dissipated energy ΔGirr, and ΔGrev/ΔGirr = 1.7–1.8. A significant degradation of superelasticity is observed in [123]-oriented crystals during the development of L21–14M–L10-transformations followed by detwinning of the L10-martensite crystals and heterophase (B2+γ) single crystals, irrespective of their orientation during the B2–L10-transition. In the latter case, martensitic transformations are characterized by a wide stress hysteresis Δσ ≥ 80 MPa and the dissipated energy exceeds the reversible energy ΔGrev/ΔGirr = 0.5. The empirical criterion, relying on the analysis of the reversible-to-irreversible energy ratio, ΔGrev/ΔGirr, during stressinduced martensitic transformations, can be used to predict the cyclic stability of superelasticity in NiFeGaCo alloys subjected to different types of heat treatment.
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