Formation mechanism of graphite nanospheres in W-C-Co system under high current pulsed electron beam irradiation

•Formation of graphite nanospheres (GNS) in W-C-Co system under HCPEB irradiation was investigated.•Two general scales of GNS were discerned in two separated composition ambiences.•The Co-rich region appeared to be nourishing for the formation of GNS. Understanding the formation mechanism of graphite nanospheres (GNS) in W-C-Co system under high current pulsed electron beam (HCPEB) irradiation is necessary for its application on surface modification of WC-Co cemented carbide. With this aim, XRD, SEM, EDS and TEM were used to investigate the effect of HCPEB irradiation on surface microstructure and phase composition. Results showed the micro-WC grains and Co were melted and transformed into nano-grained composite structure in the surface layer ∼1.29 μm. Two general scales of GNS were discerned in two types of element composition ambiences, i.e. ∼100 nm in Co-rich region and ∼50 nm in Co-poor region. Thermodynamic analysis suggested that they were the results of different routes in the non-equilibrium melting and re-solidification process.