Study of W-B-C thin films prepared by magnetron sputtering using a combinatorial approach

Abstract

X-B-C materials, where X is a transition metal such as Mo, W or Ta, have recently gained attention as possible materials for protective coatings used in material machining. In this study, a combinatorial approach was used to deposit a total of 182 coatings with a wide composition range using pulsed-DC magnetron sputtering. The coatings were prepared either in conditions, where a comparatively lower energy was delivered onto the growing coating, i.e. at ambient temperature and without applied bias, or in conditions where the coating received higher energy, i.e. at 500 °C with a bias voltage of −100 V, to study the effect of energy flow on the coating structure and properties. The coating structure was examined and four different types of diffractograms have been observed: amorphous, short range ordered, crystalline W and nanocrystalline WB2. No other crystalline phases were detected. The measured hardness of the coatings was between 9.7 and 29.7 GPa and was independent of the carbon content, however, it increased with the boron content and decreased with the tungsten content in the composition region studied. The hardest coatings exhibited an amorphous structure. The effective elastic modulus ranged from 170 to 340 GPa and increased with the boron and tungsten contents. The highest moduli were obtained for coatings exhibiting a crystalline W phase. Coatings deposited at high energy flow to the growing coating generally exhibited higher hardness and comparable elastic modulus to their counterparts with a similar composition prepared without heating or bias.