Cobalt capping on WC–Co hard metals. Part II: A technology for fabrication of Co coated articles during sintering

• A new technology for the fabrication of Co coated hardmetal articles during sintering has been developed.
• The technology permits the formation of continuous and defect-free Co coatings on the hardmetal surface.
• The transverse rupture strength of unground hardmetal articles is significantly increased.
• The fracture toughness and wettability by braze alloys of the hardmetal surface are dramatically improved.

The formation of cobalt layers on a surface of articles during sintering is designated in literature as “cobalt capping”. Although the cobalt capping phenomenon is discussed in literature, its mechanism is not well understood and there is no information on its technological implementations. A new mechanism explaining the presence or absence of cobalt layers on hard metal articles during sintering was proposed in part 1 of this paper. The understanding of the Co capping phenomenon allowed us to develop a new technology for the fabrication of Co coated hard metal articles during sintering. The technology permits the formation of continuous, ductile and defect-free Co coatings on the surface of different hard metal grades. As a result, the transverse rupture strength of unground hard metal articles is significantly increased and that of ground articles is also improved due to “healing” surface defects by the Co coatings. The fracture toughness and wettability by braze alloys of the surface of WC–Co articles are also dramatically improved due to the presence of the Co coatings.