Hardmetal composition for the preparation of thermally sprayed coatings

Thermal spray processes represent an important group of surface modification technologies to produce hardmetal coatings for wear protection. Due to the advantageous combination of moderate process temperature and high particle velocity high velocity oxy-fuel (HVOF) spraying is the preferred thermal spray process for the preparation of hardmetal coatings. WC-Co, WC-Co(Ni)Cr, Cr3C2-NiCr, and (Ti,Mo)(C,N)-Ni(Co) are the most important hardmetal compositions for coating applications. The properties of HVOF coatings of these materials are strongly influenced by chemical and metallurgical reactions during spray powder preparation and the spray process. This paper summarizes some new research results on this topic and addresses some new aspects and actual trends of the development. In particular, the following points are discussed in more detail: (1) decomposition, decarburization, and oxidation of WC-Co during the spray process and in air, (2) the effect of chromium additions to WC-Co and WC-Ni on phase composition.