Mechanical properties evaluation of chromized tungsten carbide–cobalt hardmetals

Abstract

Chromizing treatment has shown promising potential applications in the mechanical industry due to the excellent corrosion and mechanical properties provided by this process. However, the application of a chromizing process on the tungsten carbide–cobalt hardmetals has never been reported in literature. In this work, the pack chromization process has been adopted on tungsten carbide–15 wt.% cobalt (WC–15Co) hardmetals to produce a chromium containing hard surface layer. The scanning electron microscopy (SEM) and X-ray diffractometer (XRD) were employed to analyse the surface and cross-sectional morphologies and crystalline phases of chromized materials, respectively. The mechanical properties of the chromized tungsten carbide–cobalt hardmetal were evaluated by nanoindentation, Daimler-Benz Rockwell-C adhesion, scratch and pin-on-disk wear tests. It was observed that the chromizing layer was around 2 to 10 μm in thickness, which consisted of a thin (Cr,Fe) 2 N 1 − x phase in the outermost region and an underlying (Cr,Fe) 23C 6 phase after the chromization process held at 950 °C for 1 to 9 h. The hardness of the chromized hardmetals was improved effectively. In general, surface cracks on the chromizing layer should be avoided to maintain adequate mechanical properties, such as a high fracture toughness of the coating. It is concluded that the high hardness, sufficient adhesion quality and excellent wear resistance coatings were achieved by the pack chromizing process on the WC-15Co hardmetals held at 950 °C for 1 and 9 h.