Shape Memory and Superelasticity

, Volume 5, Issue 1, pp 136–146 | Cite as

Assessment of Entropy Differences from Critical Stress Versus Temperature Martensitic Transformation Data in Cu-Based Shape-Memory Alloys

  • J. L. PelegrinaEmail author
  • A. M. Condó
  • A. Fernández Guillermet


The entropy differences per unit volume (ΔStrans) between the close-packed phases in a martensitic transformation (MT) in Cu-based shape-memory alloys are obtained from mechanical tests by measuring, as a function of temperature (T), the critical resolved stress (τ). Specifically, \(\Delta S^{\text{trans}}\) values are obtained from the slope of τ versus T plots by invoking a relation which is straightforwardly derived from the classical Clausius–Clapeyron equation, viz., \(\frac{{{\text{d}}\tau }}{{{\text{d}}T}} = - \frac{{\Delta S^{\text{trans}} }}{\gamma },\) where γ is the transformation shear strain. Motivated by the significant scatter of the so obtained \(\Delta S^{\text{trans}}\) values, the thermodynamic bases of such evaluation procedure have been revised, by accounting for the nucleation step of a martensite plate. The interface, elastic strain, and chemical contributions to the Gibbs energy of nucleation have been considered. A new expression of the type \(\frac{{{\text{d}}\tau }}{{{\text{d}}T}} = {\varvec{\Omega}} - \frac{{\Delta S^{\text{trans}} }}{\gamma }\) is obtained, where the Ω term involves the elastic properties and their temperature dependence. The new \(\tau {-} T {-} \Delta S^{\text{trans}}\) relation is used to assess the \(\Delta S^{\text{trans}}\) values corresponding to the 2H/18R and 18R/6R MTs in Cu–Al–Ni and Cu–Zn–Al alloys. The ΔStrans values obtained by the present approach fall on a scatter band centered around the zero value.


Stress-induced martensitic transformation Entropy of transformation CuZnAl CuNiAl 



This study was supported by the ANPCyT, CONICET, CNEA and Universidad Nacional de Cuyo, Argentina.


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Copyright information

© ASM International 2018

Authors and Affiliations

  • J. L. Pelegrina
    • 1
    • 2
    • 3
    Email author
  • A. M. Condó
    • 1
    • 2
    • 3
  • A. Fernández Guillermet
    • 1
    • 2
    • 3
  1. 1.Centro Atómico BarilocheCNEABarilocheArgentina
  2. 2.Instituto BalseiroCNEA and Universidad Nacional de CuyoBarilocheArgentina
  3. 3.CONICETBarilocheArgentina

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