Phase analysis for the coated surface with B 4C and Y 2O 3 of cemented carbide WC-20Co in vacuum-heating was carried out by high-temperature X-ray diffraction from ambient temperature to 1300 ℃. The results show that, the high-concentration active boron atoms are released from the boron-supply agent B 4C located on the alloy surface and diffused into the γ-phase, leading to forming the three-element boron-bearing compound W 2Co 21B 6 beside forming boron-bearing compounds on the blank surface. By contrast with boronising only, the element yttrium in boronization broadens the boronising temperature range during vacuum-sintering, catalyzes the decarbonisation decomposition of B 4C and promotes diffusion of active boron atoms into the bulk of WC-Co. Phase analysis for coated surface with B 4C and Y 2O 3 of cemented carbide WC-20Co in vacuum-heating was carried out by high-temperature X-ray diffraction from ambient temperature to 1300 ° C. The results show that, the high-concentration active boron atoms are released from the boron-supply agent B 4C located on the alloy surface and diffused into the γ-phase, leading to forming the three-element boron-bearing compound W 2Co 21B 6 By contrast with boronising only, the element yttrium in boronization broadens the boronising temperature range during vacuum-sintering, catalyzes the decarbonisation decomposition of B 4C and promotes diffusion of active boron atoms into the bulk of WC-Co.