Zr-Cu thin film metallic glasses: An assessment of the thermal stability and phases' transformation mechanisms

The PVD co-sputtering technology is an efficient way to deposit Zr-Cu thin film metallic glass in a wide composition range. The structural stability and crystallization behavior of metallic glass films are investigated by in situ X-ray diffraction (XRD) via heating up to 873 K. The glassy films within the 33.3-89.1 at.% Cu range maintained their amorphous structure at temperatures higher than 550 K. Within this chemical composition range, films exhibit a smooth and dense surface morphology with 100 nm-sized grains and vein-like features. Glassy films revealed a high thermal stability as reflected by differential scanning calorimetry experiments and in situ high temperature XRD analysis. It was found that the structure evolved with the temperature and copper contents from a highly textured {1 1 1} crystallized fcc-Zr to intermetallic CuZr₂, Cu₁₀Zr₇, Cu₅₁Zr₁₄phases to finally {1 1 1} crystallized fcc-Cu. Mechanisms involved in the structural changes of the glassy films together with the multi-stage crystallization process are discussed in the light of the copper contents.