Factors controlling decarburization in HVOF sprayed nano-WC/Co hardcoatings

The mechanism of decarburization in HVOF sprayed nano-WC/Co coatings has be en investigated. The controlling factor is heterogeneous melting and locali zed superheating of the high surface area feed powder during spraying. This has the effect of causing extensive dissolution of the WC nanoparticles in the liquid Co, accompanied by rapid reaction of the dissolved G with oxyge n in the flame environment. Upon cooling down from the peak temperature in the flame, the Go-rich liquid, now deficient in C, forms W2C and/or W phase s, depending on the loss of carbon by gasification. Thus, it is concluded t hat HVOF sprayed high surface area nano-WC/Co powder is more susceptible to decarburization than conventional WC/Co powder, which is in agreement with observation. (C) 2001 Acta Materialia Inc. Published by Elsevier Science L td. All rights reserved.