Nanocrystallization in a Zr57Ti5Cu20Al10Ni8 bulk metallic glass

The first stages of thermal relaxation towards equilibrium in a Zr57Ti5Cu20 Al10Ni8 bulk metallic glass have been studied by differential scanning calo rimetry, X-ray diffraction, transmission electron microscopy and high-resol ution electron microscopy. These coupled experiments rule out for this glas s the existence of a phase separation on the nanometric scale preceding the onset of crystallization. The first step of crystallization is of the prim ary type, that is it consists of the nucleation of nanocrystallites in the amorphous matrix with which they coexist in metastable equilibrium. The ver y high nucleation rate leads to a nanometric composite structure with a num ber density of about 7 x 10 m(3) of 3-4 nm crystallites, occupying a volume fraction of about 15%. These features, as well as the crystallization kine tics observed during isochronal or isothermal heating, are discussed.