Primary crystallization process of rapidly solidified Al-Ni-Cu-Nd metallic glasses under continuous heating regime
(1. School of Materials science and Engineering,
Central South University, Changsha 410083, China;
2. Grup de Fisica de Materials I, Departament de Fisica,
Universitat Autonoma de Barcelona, 08193 Bellaterra, Spain;
3. Fisica de lEstat Solid, Facultat de Fisica, Universitat de Barcelona,
Diagonal 647, 08028 Barcelona, Spain)
Central South University, Changsha 410083, China;
2. Grup de Fisica de Materials I, Departament de Fisica,
Universitat Autonoma de Barcelona, 08193 Bellaterra, Spain;
3. Fisica de lEstat Solid, Facultat de Fisica, Universitat de Barcelona,
Diagonal 647, 08028 Barcelona, Spain)
Abstract: Rapidly solidified Al87Ni7Cu3Nd3 metallic glasses were prepared by using melt spinning. Its calorimetric behavior was characterized by using differential scanning calorimeter. The metallic glasses were partially crystallized under continuous heating regime. Primary crystallization was studied through structural characterization of the amorphous and partially crystallized ribbons by means of conventional X-ray diffraction and transmission electron microscopy with selected area electron diffraction. The results show that, the as-spun ribbons are fully amorphous and homogeneous on the micron scale, but contain high density of nanoscale quenched-in clusters or crystallite embryos. Primary crystallization mainly leads to formation of two-phase mixture of α-Al nanocrystalline and residual amorphous phase. Precipitation of α-Al nanoparticles is limited by build-up and overlapped diffusion field of solute atoms with low diffusion rate. At the earlier stage of primary crystallization the crystal nuclei exhibit high density and growth rate. With the α-Al crystal growing, the crystal growth rate decreases, and even at the later stage further crystallization into α-Al crystal becomes difficult to occur due to thermal stabilization of the residual nickel and neodymium-enriched amorphous phase, the saturated values of crystallized volume fraction and α-Al crystal diameter getting to 20%-30% and 5-15nm.
Key words: rapid solidification; Al-rich amorphous alloy; crystallization; nucleation; grain growth mechanism