Influência da solidificação rápida nas temperaturas de transformação de ligas NI-TI com efeito de memória de forma.

Abstract

Ti-Ni alloys have been attracting attention by their high performance of shape memory effect and decrease of thermal and stress hysteresis in comparison with Ti-Ni binary alloys. However, rapidly solidified Ti-Ni alloy ribbons have been known to have the shape memory effect and superelasticity superior to the alloy ingots fabricated by conventional casting. This is ascribed to the microstructural changes introduced by a rapid solidification process. Generally there are four advantages of rapid solidification over the slower conventional solidification techniques. It is considered that all of these effects have been attempted to improve shape memory effects in the rapidly solidified ribbons. Solidification structures and shape memory characteristics of Ti-Ni alloys ribbons prepared by melt spinning. The increase of the of the wheel velocity from 30 to 50 m/s results in a decrease of the ribbon thickness. When the ribbon is produced at a higher wheel velocity in melt spinning, the degree of supercooling becomes high because of its thinner thickness. The grain boundaries and defects can act as barriers to the martensitic transformation as a result of extra energy required during transformation. Thus fine-grain ribbons which have lots of grain boundaries would be expected to have lower transformation temperatures. i