Microstructure of a Partially Crystallised Ti<SUB>50</SUB>Ni<SUB>25</SUB>Cu<SUB>25</SUB> Melt-Spun Ribbon

Abstract

A low dispersion of micrometric particles embedded in the amorphous matrix is obtained by controlled thermal treatments in an initially amorphous Ti 50 Ni 25 Cu 25 melt-spun ribbon. The microstructure and crystallography of the crystalline particles have been investigated by means of TEM. Many of these particles are nearly spherical and exhibit a single crystallographic grain of austenite, the crystalline-amorphous interfaces revealing a stepped surface with preferential crystallographic planes. In addition to this, some particles with several grains in austenite have also been observed, most of them showing rather planar interfaces between adjacent grains in TEM images and twinning relationships in SAEDP. The experimental results indicate that the growth of the particular grains does not occur independently, and suggest that additional topological conditions, different from the twinning planes, yield the interfaces.

Laser annealing of amorphous NiTi shape memory alloy thin films to locally induce shape memory properties

“…Although the growth interface between the crystal and amorphous matrix looks smooth at low magnification, high-resolution TEM indicates that it actually consists of {100} B2 and {110} B2 planes. Similar growth morphologies have been found in partially crystallized Ti 50 Ni 25 Cu 25 melt-spun ribbon [17]. Quantitative EDX measurements were performed across the growth interface (Fig.…”

Crystallization in Partially Amorphous Ni<SUB>50</SUB>Ti<SUB>32</SUB>Hf<SUB>18</SUB> Melt Spun Ribbon

“…This means that the energetic cost for the nucleation of new crystals from the amorphous phase in this alloy is rather similar to the growth energy, which promotes a massive crystal nucleation almost independently of the temperature of the thermal treatment, contrary to the case of Ti 50 Ni 25 Cu 25 . 7,9) Increasing the aging time at 775 K up to 100 minutes causes a slight growth of the precipitates in the big crystals, which was not detected in previous stages (Fig. 9).…”

“…8), contrary to what was observed in Ti 50 Ni 25 Cu 25 ribbons. 7,9) Concerning the presence of crystals either in the martensitic or austenitic phase at RT in the as-spun state, the variation in the structure is mainly a consequence of the difference in the grain size (i.e. difference in the transformation temperatures).…”

“…8), which could be an indication of a not completely isotropic growth as in the Ti 50 Ni 25 Cu 25 . 9) Further aging at the same temperature promotes the full crystallization of the Ni 50 Ti 32 Hf 18 melt spun ribbon. In fact, the microstructure after 10 min at 775 K is indistinguishable from that obtained after crystallization over T C (Fig.…”

“…First works on this new attractive idea have been carried out mainly in Ti 50 Ni 25 Cu 25 . 4,5) In addition to that, further investigations have also been performed on initially (partially) amorphous [6][7][8][9][10] or crystallized [11][12][13] Ti 50 Ni 25 Cu 25 ribbons. On the other hand, most investigations on the crystallization of Zr-Ti-Ni based alloys have been performed away from compositions giving martensitic transformation (see Inoue 14) for a general overview about bulk metallic glasses).…”