Fabrication and characterization of superhard tungsten boride layers deposited by radio frequency magnetron sputtering

The most promising areas of research of new super-hard materials are transition metal borides. These materials are one of the candidates for future superhard layers that will be competitive to DLC and c-BN layers. In this paper MoB-type tungsten boride (WB) layers were examined. WB layers have been deposited by radio frequency magnetron sputtering on Silicon (100), 304 stainless steel (SS 304) and Inconel 601 substrates. Measured thickness of herein prepared layers was about 1 µm, and all studied samples were dense, uniform and smooth. Surface investigation was performed by using an optical profilometer, atomic force microscopy, and scanning electron microscopy. The structure analysis was examined by using X-ray diffractometer (XRD) and transmission electron microscopy (TEM) techniques. Results from the XRD and TEM analysis showed that WB layers were dominated by (101) reflection and indicated a fine grain structure with a grain size of 20–40 nm. The effect of target sputtering power and ambient gas pressure was investigated. The hardness of WB layers deposited on silicon substrate was compared under the load from 1 mN to 5 mN. The hardness of WB layers deposited on SS 304 and Inconel was measured up to 50 mN. All layers of WB revealed excellent hardness exceeding 40 GPa.