Properties of HVOF sprayed TiC and TiB2-based cermet coatings
This work reports research concerning the properties of cermet coatings deposited by high velocity oxy-fuel spraying, which are designed to exhibit resistance to abrasive wear and high-temperature oxidation. Cermet powders have been produced by self-propagating high-temperature synthesis (SHS) reaction of elemental powder mixtures of Fe, Cr, Ti and C or B, to produce a cermet, containing an Fe(Cr) binder phase and a hard ceramic phase, TiC or TiB2. The Ti and C content in the powder mixtures were varied in order to evaluate the effect of the C: Ti ratio of TiC on the overall integrity of three different feedstock powders and coatings produced. Four cermet coatings were produced from these SHS powders, one TiB2-based and three TiC-based. Abrasive wear resistance of the coatings was evaluated using a dry sand rubber wheel (DSRW) abrasive wear testing machine, where the coatings were subjected to abrasion by both alumina and silica abrasives. The TiB2-based coating exhibited superior wear resistance when subjected to both alumina and silica. Of the TiC-based coatings, the equimolar coating exhibited superior resistance when subjected to alumina, and the excess Ti coating exhibited superior wear resistance when subjected to abrasion with silica. When compared with coatings produced from commercially available powders, namely, sintered and crushed WC-Co and blended NiCr-Cr3C2, the coatings produced from SHS powders exhibited comparable, and in some cases, better abrasive wear properties. Preliminary oxidation tests showed that all four coatings performed well at 500°C (the temperature at which WC-Co begins to degrade rapidly). They exhibited some oxidation at 700°C, and at 900°C, exhibited severe oxidation.