Fabrication of WC-Co coatings by cold spray deposition

Processing of cermet such as WC-Co is not easy by cold (gas dynamic) spraying although cold spray process can eliminate the degradation of the phase as compared to conventional high velocity oxy-fuel (HVOF) spraying process. In this study, WC-12∼17%Co powders with nano- and microstructures were deposited by cold spray process using nitrogen and helium gases. Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out by SEM and X-ray diffraction (XRD). The results show that there is no detrimental phase transformation and/or decarburization of WC by cold spray deposition as expected. It is also observed that nano-sized WC in the feedstock powder is maintained in the cold sprayed coatings. It seems that nano-sized WC is advantageous over micro-sized WC for cold spray deposition because higher particle velocity can be obtained with the same gas velocity. It is demonstrated that it is possible to fabricate the nano-structured WC-Co coating with low porosity and very high hardness (∼2050 HV) by cold spray deposition with reasonable powder preheating.