Effect of copper on the thermal stability and non-isothermal crystallization behavior of Al86Ni10-xCuxRE4 (x = 0.5–2.5) amorphous alloys prepared by melt spinning

Microstructural features, thermal stability and crystallization kinetics of various melt spun Al-based alloys containing transition metals (TM = Ni, Cu) and Ce-based rare earth metals (MM: Misch Metal) were investigated via X-ray diffractometry (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). It is shown that the extended topological instability of Egami-Waseda model (λ criterion) is a useful tool to predict the crystallization behavior of the prepared alloys. FCC-Al nanoparticles are formed during the initial crystallization process. Calculation of the apparent activation energy using the Kissinger method indicates that partial replacement of nickel by copper decreases the thermal stability. The thermal stability in the presence of copper, however, can be improved by increasing the MM content. On the other hand, TEM studies determine that copper reduces the average size of FCC-Al nanocrystals from ~50 nm in Al86Ni10MM4 to ~35 nm in Al86Ni9Cu1MM4 amorphous alloy. Thermodynamic evaluation of the crystallization process and determination of the local crystallization index reveal that the primary crystallization in amorphous Al-based alloys containing MM, Ni and Cu is a complex diffusion controlled process.