Synthesis of nano structural WC-Co powders from water soluble precursors: effects of carbon content to chemical and phase structure

Thermal sprayed cemented carbides such as WC-Co(Cr) and Cr3C2-NiCr coatings are well known and widely used for wear protection purposes. Submicron and nano-sized carbides in cermets have shown promising results in hardness and wear performance. Presented study is a part of the research aiming to create a new novel powder manufacturing route for homogenous nano WC + Co matrix powder for thermal spraying. In the novel precursor method controlling the exact amount of carbon is one major challenge. Carbon control is a crucial issue, suppressing the sub-stoichiometric carbide formation, but also avoiding weakening the effect of extra free carbon in the structure. The goal of this study was to synthesize nano structural WC-Co powders from water soluble precursors and compare the effects of carbon content to chemical and phase structure of the final products. Powders were manufactured via spray drying method from water based solution, with raw materials ammonium meta tungstate (AMT) as a tungsten source, glycine as a carbon source and cobalt acetate as a cobolt source. Dried products were heat treated in Ar atmospheres. The thermal decomposition of the precursors was studied by using thermogravimetry (TGA) and evolved gas analysis with interconnected mass spectrometer. The morphology and particle size were studied with scanning electron microscopy (SEM) and laser diffraction, and phase structures were analyzed by an X-ray diffractometry (XRD). Carbon and oxygen content were analysed with LECO CS-230 with an infrared detector.