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Chemically disordered uniform promotes negative temperature-dependent superelasticity in shape memory alloys.
- Source :
-
Acta Materialia . Aug2024, Vol. 274, pN.PAG-N.PAG. 1p. - Publication Year :
- 2024
-
Abstract
- An increasing number of studies on shape memory alloys (SMAs) have shown anomalous temperature dependence of superelasticity, i.e., the superelastic stress with temperature (d σ /d T) deviates from the behavior expected from the Clausius–Clapeyron relationship, especially showing a negative d σ /d T at low-temperatures. However, the underlying mechanism is still experimentally unclear. Here, we perform large-scale molecular dynamic (MD) simulations of NiTi-based SMAs to elucidate the relationship between the observed negative d σ /d T and fluctuation in chemical concentration. By comparing the superelastic behavior of Ni 50 Ti 47.2 Nb 2.8 SMAs, in which the solution Nb atoms are either disordered uniformly or nano-scale undulated, we find that the chemically disordered uniform can promote the d σ /d T deviation. It stems from that the disordered uniformed solid-solution atoms with relatively high concentrations of a homogenously lattice-level strain field at low temperatures can remarkably refine the martensite embryo over several lattice units. The phase transformation then undergoes a form of continuous transformation. In this sense, the formation of mature martensite is delayed upon loading, thus increasing the critical superelastic stress. Such a kinetic effect will be accentuated as the temperature decreases. Our findings highlight the importance of homogenization of heat treatment for the design of ultra-low temperature superelastic SMAs. [Display omitted] [ABSTRACT FROM AUTHOR]
- Subjects :
- *SHAPE memory alloys
*HEAT treatment
*LOW temperatures
*MARTENSITIC transformations
Subjects
Details
- Language :
- English
- ISSN :
- 13596454
- Volume :
- 274
- Database :
- Academic Search Index
- Journal :
- Acta Materialia
- Publication Type :
- Academic Journal
- Accession number :
- 177752957
- Full Text :
- https://doi.org/10.1016/j.actamat.2024.120030