Study On Fabrication Process Of Gradient Ultrafine Cemented Carbide Without Eta-Phase

Gradient Cemented carbide which has advantages of high wear resistance on surface and high strength in core is widely concerned by researshers. In this paper, fabrication process of gradient ultrafine cemented carbide without eta-phase was researched based on ultrafine cemented carbide with10wt.%Co and0.6WC particle size.The method of quantitative evaluation of the cobalt-phase gradient structure and WC grain size was studied. The results show that, scaning surface mode can be used for the quantitative evaluation of the cobalt gradient in cemented carbide. By using IMAGEJ software, line intercept method is covenient and accurate to measure WC grain size in ultrafine cemented carbide with the BSE images under5000magbifications.The feasibility of preparing gradient ultrafine cemented carbide without eta-phase by carbusintering was analyzed. A exploratory experiment was done. The preparation process was optimized on the basis of the exploratory experiment. The results show that, it is available to prepare gradient ultrafine cemented carbide without eta-phase by carbusintering. With the carburization temperature and time elevated, thickness of gradient layer, cobalt depleted amplitude and WC grain size increase. With concentration of CH4and mixed gas flow rate increased, thickness of graded layer and lean cobalt amplitude decrease. After carburized, WC grain size on the surface is less than that in the core mostly. The best process paramater(temperature, time, atomosphere concentration, rate of flow) is1320℃,240min,1.2%and8L/min. The influence degree of these factors is temperature> atmosphere concentration> time> rate of flow.The formation mechanism of cobalt gradient structure in preparing gradient ultrafine cemented carbide without eta-phase by carbusintering was analyzed. The results show that, when carburized in solid phase temperature, the formation mechanism of gradient cobalt-phase distribution is mainly ascribed to solution and precipitation of W and C atoms on WC grains in γ-phase. When carburized in solid-liquid coexistence temperature, solution and precipitation of W and C atoms, as well as the pressure force from the difference quantities of liquid between the surface and the core section, form the cobalt-phase gradient structure in ultrafine cemented carbide without eta-phase.