NIMS and Fujimi Co-develop High Performance WC-Co Coating

National Institute for Material Science (NIMS), Japanese independent administrative institution, currently announced NIMS and Fujimi Incorporated, Aichi based maker of lapping and polishing agents, co-developed new WC-Co coating (WC: tungsten carbide, Co: cobalt) with high hardness and smoothness. New coating could be adopted to industrial machines, construction machines and automotive shafts.

WC-Co alloy is a material for cemented carbide tools while WC-Co powder is a material for wear-resistant coating of excavators or industrial rolls in steel and paper plants. New WC-Co coating achieved Vickers hardness of Hv 1,600 or more and surface roughness of Ra 1.8 micrometers or less. Averaged figures of conventional WC-Co coating are Hv 1,200 and Ra 3.5 micrometers.

Conventional WC-Co coating is obtained by a process called thermal spraying. The problem is that cobalt melts during thermal spraying and forms weak binder in the coating by reaction with tungsten carbide. Another problem is that thermal spraying equipment is not suitable for using very thin WC-Co powder though thinner powder realizes higher coating performance. Particles adhere to the inside of thermal spraying nozzle and make it impossible to continue operation for long hours.

NIMS developed a new process named Warm Spray to control temperature of spraying gas more precisely than ever. Under this process, cobalt is well controlled not to melt while particles can be sprayed at the speed as high as 500 meters per second or more. Fujimi Incorporated developed 5-20 micrometers diameter particles, the most suitable size for Warm Spray process. These technologies realized dramatic improvement of WC-Co coating performances.