Decomposition and crystallization of Pd40Cu30Ni10P20 and Zr46.8Ti8.2Cu7.5Ni10Be27.5 metallic glasses

The Pd40Cu30Ni10P20 and Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glasses exhibit extraordinary stability against crystallization. It is assumed, that this results from the complicate crystallization behavior, which requires strong decomposition of the glass in some cases already preceding to the crystallization. The crystallization behavior of both these glasses in its first stage is studied after different thermal treatments by means of differential scanning calorimetry, XRD, transmission electron microscopy, energy-filtered transmission electron microscopy and three-dimensional atom probe. During annealing for long times at temperatures above and below the calorimetric glass transition respectively both metallic glasses undergo decomposition. Nanometer-scaled amorphous regions are observed sporadic or homogeneously distributed in the respective glasses. They differ in composition from their amorphous environment. After extended annealing or short time heat treatment at higher temperatures nano-crystals form from these regions. The composition of these crystals resembles the compositions of the decomposed regions. In case of Pd–Cu–Ni–P the crystals accord with an intermetallic phase. In case of Zr–Ti–Cu–Ni–Be, they are quasicrystalline. Depending on the pre-annealing treatment of the Zr–Ti–Cu–Ni–Be glass three different types of quasicrystals are found. For both alloys long-range diffusion over a wide concentration range is one important factor which controls the decomposition kinetics. Thus diffusion contributes essentially to the stability of the glasses and effects the pathway of crystallization and the resulting microstructure.