1. Metastable effects on martensitic transformation in SMAs
- Author
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V. Torra, Francisco C. Lovey, F. Martorell, Marcos Sade, Aslan Ahadi, and Qingping Sun
- Subjects
Materials science ,Ciencias Físicas ,02 engineering and technology ,HEAT CAPACITY ,01 natural sciences ,Heat capacity ,NITI ,Stress (mechanics) ,Latent heat ,SMA ,THINNER AND THICK WIRES ,Physical and Theoretical Chemistry ,Composite material ,Binodal ,Metallurgy ,MARTENSITIC TRANSFORMATION ,Dissipation ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,S-SHAPED CYCLES ,Grain size ,010406 physical chemistry ,0104 chemical sciences ,Astronomía ,GRAIN SIZE ,LATENT HEAT ,Nickel titanium ,Diffusionless transformation ,0210 nano-technology ,CIENCIAS NATURALES Y EXACTAS - Abstract
The transformation and retransformation paths realized at constant stress in wires of NiTi SMAs show a horizontal or “flat” behavior in the hysteretic cycle. After sinusoidal cycling at 0.01 Hz (i.e., training) with a maximal strain of 8 %, the thicker wires of NiTi SMAs, with a diameter of 2.46 mm, have the stress–strain cycles with one S-shaped behavior. A “similar” change appears by varying the grain sizes in the samples, i.e., from 80 to 20 nm. Furthermore, the local measurements of temperature suggest that cycling induces changes in the transformation mechanisms associated with the evolution from horizontal to S shape. For instance, the associated energy evolves from localized transformation to homogeneous heat production in S-shaped cycles. Thermodynamic analysis establishes a link between heat capacity and the slopes of the coexistence curve in f–x or in σ–ε via the (∂ε/∂σ)coex. The flat cycles were coherent with the classical latent heat, i.e., dissipation at constant stress. In the S-shaped cycles, the heat during the phase change seems redistributed as heat capacity against progressive stress. Preliminary direct measurements are coherent with the evolution of the (∂ε/∂σ)coex against strain. Fil: Torra, Vicenç. Personal Research Group; España Fil: Martorell, F.. Personal Research Group; España Fil: Sun, Q. P.. Hong Kong University of Science and Technology; República de China Fil: Ahadi, A.. Tsukuba University. National Institute For Materials Science; Japón. Wuhan University; China Fil: Lovey, Francisco Carlos. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina Fil: Sade Lichtmann, Marcos Leonel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina
- Published
- 2016
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