High Temperature Shape Memory Effect in Ruthenium Alloys

摘要

The shape memory effect is observed in alloys which undergo a thermoelasticmartensitic transformation. This transformation is characterized by the continuous growth of martensite plates as the temperature is lowered and, comparably, the continuous disappearance of these martensite plates as the temperature is subsequently raised. The reversible nature of this transformation can lead to the many interesting features of the shape memory effect. One effect is superelasticity, which occurs above the transformation temperature and consists of the activation of the martensitic transformation in response to an external stress. Any shape changes produced during the transformation are reversed upon release of the external stress. Below the transformation temperature, the material can exhibit a one way or two-way shape memory effect The one-way shape memory effect exists when the material is deformed below the martensitic transformation temperature and then reverts to its original shape upon heating to above the transformation temperature. With appropriate mechanical and thermal training of the material this effect can be modified into a two-way shape memory effect. This two way effect is a reversible shape change which results during both heating and cooling the material through the transformation temperature range.