Nanocrystallization in magnetron sputtered Zr–Cu–Al–Ag thin film metallic glasses

Abstract

Zr-based thin film metallic glasses (TFMG) were fabricated from a polycrystalline Zr₄₈Cu₃₆Al₈Ag₈ (at.%) target by DC magnetron sputtering. A series of characterization techniques were employed to study the structure, composition and thermal stability of the glassy coating and also the mechanical compliance of the TFMG over stainless steel. X-ray diffraction indicated a completely amorphous microstructure. However, specimens prepared for plan-view TEM revealed nanocrystallites of the CuZr₂ phase dispersed in an amorphous matrix. Annealing experiments showed that the primary phase to nucleate in the films is the CuZr₂ phase as observed from XRD data. The film/substrate interface did not show any inter-diffusion, as confirmed by high resolution scanning TEM. Calorimetric studies by DSC showed a large supercooled liquid region of about 83 K. Surface morphological studies by both FE-SEM and AFM indicated a very smooth surface devoid of pores or cracks, with an average roughness of about 1.25 nm. X-ray photoelectron spectroscopy (XPS) showed oxygen on the film surface; both Zr and Al revealed non-metallic bonding peaks concomitant with a mixed or bilayer oxide on the surface. A very high scratch resistance was observed for the specimen coated over stainless steel substrates.