In-situ Preparation of Ultra-fine YG6 Cemented Carbide via Sintering of WC-6Co Composite Powder

The in-situ preparation of WC-6Co composite powder was subjected to dry-bag type cold iso-static pressing without any pre-treatment (The pressing pressure was 1×108 Pa and the holding time was 15 s). Ultra-fine YG6 cemented carbide was prepared by sintering the pressed blank in a low-pressure sintering furnace at a sintering temperature of 1360℃ for40 min, and it was kept under 5 MPa pressure holding for 20 min. The morphology, metallography and physical mechanics properties of the YG6 cemented carbide were analyzed. The results show that abnormal grain growth can be observed from the ultra-fine YG6 cemented carbide, and the average grain size of the WC alloy is 0.8 μm. The hardness (HV30) is (21500±100) MPa, which is higher than that of the conventional ultra-fine YG6X cemented carbide. Then, the composite powder of WC-6Co was used to produce ultra-fine size YG6 cemented carbide by processes of wet-milling, pressure type spray drying, binder adding, extrusion forming, and low-pressure sintering. The effects of different grain growth inhibitor ratios, ball-milling time, extrusion pressure and sintering temperature on the properties of the alloy were investigated. The results show that when 0.3 wt% VC and 0.8 wt% Cr3C2 are added, wet milling time is 48 h, extrusion is at 24 MPa pressure and sintering temperature is 1340℃, the produced ultra-fine YG6 cemented carbide has homogeneous WC grain size, and no WC grains with abnormal growth can be observed from the OM image of the YG6 cemented carbide. The average grain size of WC alloy is 0.4 μm, and the grains are in polygonal shapes with relatively round outlines. The strength and hardness of YG6 cemented carbide prepared under these conditions are the highest. The TRS of YG6 cemented carbide is (2250±20) MPa, and the hardness (HV30) is (22600±100) MPa. Intergranular fracture, along the WC and WC grain boundary fracture or WC and Co grain boundary fracture can be observed from the morphology of fractures. © 2020, Science Press. All right reserved.