Characterization of the W2C phase formed during the high velocity oxygen fuel spraying of a WC+12 pct Co powder

A variety of experimental techniques have been used to study a WC-12 pet Co powder and the coatings produced by high velocity oxygen fuel (HVOF) spray ing of the powder onto a steel substrate, Many of the structural characteri stics of the powder were also found in the coating. However, when the metal lic matrix of the powder was melted during thermal spraying, the carbides w ere partially dissolved and a very heterogeneous liquid phase was produced in which the W/C ratio varied from about 1 to 4. These variations have been Linked with oxidation of the liquid phase during spraying. The factors inf luencing the formation of W2C in the coating have been identified as (1) an in situ transformation of WC into W2C maintaining the original WC faceted morphology and (2) the precipitation of W2C from the W-rich liquid phase ma trix as the coating cools. A cobalt containing carbide of the M6C-M12C type has also precipitated from the liquid phase when the W/C and W/Co ratios w ere high.