A study of an amorphous-crystalline structured Ti–25Ni–25Cu (at.%) shape memory alloy

Amorphous Ti–25Ni–25Cu (at.%) melt-spun ribbons have been annealed for various times below the crystallization temperature. The arising amorphous-crystalline microstructures have been characterized by means of transmission electron microscopy (TEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and optical metallography. The crystallization occurred in form of spherical B 19-martensite grains surrounded by amorphous matrix. Subnanometric plate-like precipitates were formed inside of the martensite grains. Their density increased with the annealing time leading to embrittlement. The fully crystallized ribbons still contain the B2-phase. Two-stage transformation behavior has been found and is discussed with respect to the observed microstructures.