Intermetallic β-Ti3Au hard thin films prepared by magnetron sputtering

In the current study, we report on a deposition method to synthesize the intermetallic beta-Ti3Au thin films by magnetron sputtering. We examine thin films crystallinity and structure-property relationships in terms of deposition conditions. The study is motivated by the vast application potential of beta-Ti3Au, known to possess high hardness, interesting scratch and wear behaviors, and very good biocompatibility. The Ti1-xAux thin films (x = 0-1) were deposited onto the Si(100) substrates by triple target magnetron sputtering under an Ar atmosphere and temperature varying from room temperature and to 650 degrees C. The samples were characterized by X-ray diffraction (XRD) under grazing incidence and Bragg-Brentano geometries, scanning and transmission electron microscopy (SEM, TEM) equipped with an energy dispersive spectroscopy detector (EDS), and depth-sensing nanoindentation to investigate the dependence of the phase configuration, microstructure and mechanical properties on the Au/Ti ratio and deposition temperature. It was shown that upon varying the Au content the coatings develop a variety of single-phases or mixed structures composed of cubic, hexagonal and/or tetragonal phases of the binary Au-Ti system. At x = 0.25, the compound Ti3Au developed a quasi-amorphous or defective nanocrystalline structures when deposited at room or low-temperatures, while a fully crystalline beta-Ti3Au with an A15-type structure and lattice parameter of a = 0.50925 nm was obtained when deposited at 350-400 degrees C. The beta-phase films exhibited a hardness of 10.4-12.1 GPa, which is among the upper limits for intermetallic compounds, while the Young's modulus (173-201 GPa) is fairly comparable to 209 GPa predicted by first principles theoretical calculations. Thin film crystallinity and hardness strongly influenced both the deformation mode and the wear behavior under nanoscratch testing. The wear mechanisms changed from ploughing with ductile displacement, to microcutting with the formation of curly debris, to cracking with brittle fragmentation.