Inductive flash-annealing of bulk metallic glasses

We developed a temperature-controlled inductive flash-annealing device, which heats bulk metallic glasses (BMGs) at defined rates of up to 200 K/s to a given temperature. Subsequent instantaneous quenching in water allows preserving the microstructures obtained at various stages of crystallization. One Zr-based and two CuZr-based BMGs were flash-annealed at the onset of crystallization with different heating rates in order to prepare advanced BMG-matrix composites. The highly reproducible composite microstructures contain uniformly dispersed crystals and a narrow crystal size distribution. In order to assess the limitations of the present process, which mainly originate from non-uniform inductive heating, the skin depth was calculated. It is determined to be about 2.3 mm, which enables flash-annealing of rather bulky samples. The cooling rate was estimated from the interlamellar spacing of eutectic Al-Cu alloys to be on the order of 10³ K/s. This ensures that decomposition of the microstructure during quenching is prevented. The present flash-annealing procedure is applicable to a wide variety of glass-forming liquids and has a large potential for tailoring the microstructure and, consequently, the mechanical properties of BMG-matrix composites.