### Abstract

A method for the determination of the equilibrium transformation temperature (T_{0}) in CuAlNi single crystalline alloys, by traditional uniform heating and cooling of the specimen under constant uniaxial applied stress, σ, is presented and the T_{0}(σ) functions are constructed. Above a certain stress level the phase transformations, even in a multiple interface mode, can be driven in such a way that the thermal hysteresis loops have a rectangular part, from which T_{0} can be determined via the well-known relation: T_{0} = (M_{s} + A_{f})/2, where M_{s} and A_{f} are the martensite start and austenite finish temperatures, respectively. At low stress values the heating up branch of the hysteresis is different; it starts with a vertical part showing that the beginning of the austenite formation is free of the release of the elastic energy (this takes place only in the second part of this branch). Here the T_{0} temperature can be determined as the arithmetic mean of M_{s} and the austenite start temperature, A_{s}. Using the experimentally determined stress dependence of the transformation strain, the T_{0} vs. σ function was also constructed from the Clausius-Clapeyron relation and this curve fitted very well to the points obtained from the above relationships at high and low stress levels, respectively. The stress dependence of the non-chemical energy contributions to the phase transformation are also determined. It is shown that integrals of the differential values (the derivatives of the energy contributions by the transformed fraction) give self-consistent results with the (integral) quantities directly measured in differential scanning calorimetry (DSC) experiments or obtained from the area of the hysteresis loops.

Original language | English |
---|---|

Pages (from-to) | 1823-1830 |

Number of pages | 8 |

Journal | Acta Materialia |

Volume | 55 |

Issue number | 5 |

DOIs | |

Publication status | Published - Mar 2007 |

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### Keywords

- Martensitic phase transformation
- Shape memory alloys
- Thermodynamics
- Thermomechanical processing

### ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Materials Science(all)
- Metals and Alloys

### Cite this

_{0}) and analysis of the non-chemical energy terms in a CuAlNi single crystalline shape memory alloy.

*Acta Materialia*,

*55*(5), 1823-1830. https://doi.org/10.1016/j.actamat.2006.10.043

**Determination of the equilibrium transformation temperature (T _{0}) and analysis of the non-chemical energy terms in a CuAlNi single crystalline shape memory alloy.** / Palánki, Z.; Daróczi, L.; Lexcellent, C.; Beke, D.

Research output: Contribution to journal › Article

_{0}) and analysis of the non-chemical energy terms in a CuAlNi single crystalline shape memory alloy',

*Acta Materialia*, vol. 55, no. 5, pp. 1823-1830. https://doi.org/10.1016/j.actamat.2006.10.043

}

TY - JOUR

T1 - Determination of the equilibrium transformation temperature (T0) and analysis of the non-chemical energy terms in a CuAlNi single crystalline shape memory alloy

AU - Palánki, Z.

AU - Daróczi, L.

AU - Lexcellent, C.

AU - Beke, D.

PY - 2007/3

Y1 - 2007/3

N2 - A method for the determination of the equilibrium transformation temperature (T0) in CuAlNi single crystalline alloys, by traditional uniform heating and cooling of the specimen under constant uniaxial applied stress, σ, is presented and the T0(σ) functions are constructed. Above a certain stress level the phase transformations, even in a multiple interface mode, can be driven in such a way that the thermal hysteresis loops have a rectangular part, from which T0 can be determined via the well-known relation: T0 = (Ms + Af)/2, where Ms and Af are the martensite start and austenite finish temperatures, respectively. At low stress values the heating up branch of the hysteresis is different; it starts with a vertical part showing that the beginning of the austenite formation is free of the release of the elastic energy (this takes place only in the second part of this branch). Here the T0 temperature can be determined as the arithmetic mean of Ms and the austenite start temperature, As. Using the experimentally determined stress dependence of the transformation strain, the T0 vs. σ function was also constructed from the Clausius-Clapeyron relation and this curve fitted very well to the points obtained from the above relationships at high and low stress levels, respectively. The stress dependence of the non-chemical energy contributions to the phase transformation are also determined. It is shown that integrals of the differential values (the derivatives of the energy contributions by the transformed fraction) give self-consistent results with the (integral) quantities directly measured in differential scanning calorimetry (DSC) experiments or obtained from the area of the hysteresis loops.

AB - A method for the determination of the equilibrium transformation temperature (T0) in CuAlNi single crystalline alloys, by traditional uniform heating and cooling of the specimen under constant uniaxial applied stress, σ, is presented and the T0(σ) functions are constructed. Above a certain stress level the phase transformations, even in a multiple interface mode, can be driven in such a way that the thermal hysteresis loops have a rectangular part, from which T0 can be determined via the well-known relation: T0 = (Ms + Af)/2, where Ms and Af are the martensite start and austenite finish temperatures, respectively. At low stress values the heating up branch of the hysteresis is different; it starts with a vertical part showing that the beginning of the austenite formation is free of the release of the elastic energy (this takes place only in the second part of this branch). Here the T0 temperature can be determined as the arithmetic mean of Ms and the austenite start temperature, As. Using the experimentally determined stress dependence of the transformation strain, the T0 vs. σ function was also constructed from the Clausius-Clapeyron relation and this curve fitted very well to the points obtained from the above relationships at high and low stress levels, respectively. The stress dependence of the non-chemical energy contributions to the phase transformation are also determined. It is shown that integrals of the differential values (the derivatives of the energy contributions by the transformed fraction) give self-consistent results with the (integral) quantities directly measured in differential scanning calorimetry (DSC) experiments or obtained from the area of the hysteresis loops.

KW - Martensitic phase transformation

KW - Shape memory alloys

KW - Thermodynamics

KW - Thermomechanical processing

UR - http://www.scopus.com/inward/record.url?scp=33846910307&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33846910307&partnerID=8YFLogxK

U2 - 10.1016/j.actamat.2006.10.043

DO - 10.1016/j.actamat.2006.10.043

M3 - Article

VL - 55

SP - 1823

EP - 1830

JO - Acta Materialia

JF - Acta Materialia

SN - 1359-6454

IS - 5

ER -