To study phase formation up to 2300K, tungsten carbide–cobalt (WC–Co) samples were exposed to concentrated solar radiation in hydrogen plasma. The reducing atmosphere was a non-equilibrium hydrogen plasma created in a microwave cavity at the nominal power of 1000W. The dissociation fraction of hydrogen molecules in plasma was of the order of 10% assuring for almost optimal reduction of any oxide that could be formed on the surface of samples due to the residual atmosphere. Micro-structural characterization was performed by XRD and AES depth profiling. The results showed the appearance of Co 6 W 6 C phase at the temperature of 1050±50K. This phase almost vanished at the temperature of 1300±90K and was replaced by the Co 3 W 3 C phase. This phase vanished at 1690±150K where only WC and Co peaks were detected by XRD. The AES depth profiles showed enrichment of the surface film with Co at elevated temperatures. At extremely high temperature of 2300K, the Co vanished from the surface layer but remained in crystalline form in the bulk material. SEM imaging showed an evolution of the material crystallinity up to perfectly recognizable crystals of the dimension of approx. 1μm at the maximum temperature. The results are explained by mobility of Co atoms, surface segregation and sublimation at very high temperature.