Effect of Electropulse Treatment on Properties of Melt-spun TiNiCu Ribbons for Micromechanical Applications

Rapidly quenched thin ribbons of quasi-binary TiNi–TiCu system alloys with high copper contents (more than 20 at.%) are promising materials for the manufacture microactuators due to excellent shape memory effect with narrow temperature hysteresis. Amorphous TiNiCu alloys with a copper content of 30–40 at.% were obtained by the melt spinning technique at a melt cooling rate of 10
⁶
K/s in the form of ribbons with a thickness of about
$40\ \mu\mathrm{m}$
. The crystallization of the alloys was carried out using electropulse treatment with duration in the range from 5 to 1000 ms. X-ray diffraction studies showed that at room temperature all alloys exhibit B19 martensitic structure. Microstructure of the ribbons consists of columnar crystals near the ribbon surfaces and large grains with characteristic sizes from 3 to
$12\ \mu\mathrm{m}$
. TEM examination revealed a subgrain structure with nanoscale martensite plates (20-80 nm). The alloys exhibit one-stage martensitic transformation
$\mathrm{B}2\leftrightarrow \mathrm{B}19$
and pronounced shape memory effect in the temperature range of 55-75°C.