|
|
PHASE EVOLUTION IN Ni-48 at.% TI SHAPE MEMORY ALLOY PREPARED BY SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS
Karlík, M. ; Haušild, P. ; Beran, Přemysl ; Novák, P. ; Čapek, J. ; Kučera, V. ; Kopeček, Jaromír
In Ni rich Ni–Ti alloys, various phases such as hexagonal Ni3Ti, cubic NiTi2 and rhombohedral Ni4Ti3 appear during heat treatment. The presence of these precipitates affects the shape memory effect and superelasticity in an important manner. In this paper we present a study of the phase evolution during annealing of the Ni–48at.%Ti shape memory alloy elaborated by self-propagating high-temperature synthesis (SHS). Morphology and crystallography of the phases were examined by means of light metallography, scanning electron microscopy (SEM), neutron and X-ray diffraction, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Besides the phases mentioned in the\nliterature, a Ni-rich phase with the composition near Ni3Ti2 stoichiometry and having a cubic symmetry was found. This phase develops from Ni4Ti3 particles during slow (furnace) cooling from the temperature of 1000 °C. Its particles have the form of thin platelets coherent with the (B2) NiTi matrix. The orientation relation is either cube-to-cube, [111]P || [115]B2 and (1-10)P || (1-10)B2 or [011]P || [011]B2 and (1-10)P || (1-41)B2.\n
|
guest ::
