On the multiplication of dislocations during martensitic transformations in NiTi shape memory alloys

Thermomechanical modeling of polycrystalline SMAs under cyclic loading, Part I: theoretical derivations

Publisher Summary This chapter discusses vibrational properties of shape-memory alloys. The crystal structure of a given material depends on its energy and also its entropy, which plays an increasingly important role as temperature is raised. In the case of nonmagnetic metallic systems, the entropy has two major contributions: the electronic contribution arising from electronic states near the Fermi level and the vibrational contribution, related to the vibrations of the atoms around their equilibrium positions in the crystal lattice. The present chapter is concerned with a class of bcc-based metallic alloys, commonly called shape-memory alloys. These materials have the unique property of being able to recover from large deformations by slightly increasing their temperature. The physical mechanism behind this effect is a diffusionless, first-order structural transition, usually referred to as the martensitic transition. Martensites form when a high-temperature crystalline phase undergoes a first-order phase transition to a lower symmetry crystalline phase. This structural phase transition usually proceeds by means of the nucleation of the new phase within the initial one, and may be induced either by changing the temperature or by applying a mechanical stress.

Vibrational properties of shape-memory alloys

Shape memory in Cu-based alloys: phenomenological behavior at the mesoscale level and interaction of martensitic transformation with structural defects in Cu-Zn-Al

The effect of heat treatment on the martensitic transformation behaviour of NiTi has been investigated. Transformation temperature measurements are interpreted in terms of the chemical, elastic and irreversible components of the overall transformation free energy change. It is shown that the occurrence of a two-stage parent-R-martensite transformation on cooling and a single-stage reverse transformation in specimens annealed at intermediate temperatures is a consequence of the irreversible energy loss associated with the martensitic transformation. The increase in the R transformation temperature in specimens heat treated at low temperature is shown to result from changes to the reversible, elastic or chemical, components of the transformation free energy change.

Thermodynamic analysis of the martensitic transformation in NiTi—I. Effect of heat treatment on transformation behaviour

On the characterization and origin of the dislocations associated with the two way memory effect in CuZnAl thermoelastic alloys-I. Quantitative analysis of the dislocations

On the characterization and origin of the dislocations associated with the two way memory effect in CuZnAl thermoelastic alloys—II. The model for the formation of dislocations

D. Ríos-Jara

Papers

On the characterization and origin of the dislocations associated with the two way memory effect in CuZnAl thermoelastic alloys-I. Quantitative analysis of the dislocations

On the characterization and origin of the dislocations associated with the two way memory effect in CuZnAl thermoelastic alloys—II. The model for the formation of dislocations