Study On Optimization Of Fabrication Process And Performance Of Gradient 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 researchers and industrial circle in recent decades. In this paper,optimization of fabrication process and performance of gradient cemented carbide without eta-phase was researched based on cemented carbide with10wt.%Co and0.8μm WC particle size.The optimization of process parameters for fabricating gradient ultrafine cemented carbide without eta-phase was studied by Taguchi method. The results show that, during the fabrication of gradient ultrafine cemented carbide without eta-phase, temperature is highly significant factor for thickness and amplitude of cobalt gradient, the volume fraction of methane has high remarkable effect on thickness of the gradient zone, the time has certain effect on thickness of the gradient zone, and the flow rate of mixed gases is insignificant to both thickness and amplitude of cobalt gradient. Both the thickness and the amplitude of the gradient increase with increasing temperature and time, and decrease with increasing volume fraction of methane, and first increase then decrease with increasing flow rate of mixed gases. Under the condition of this study, the combination of the optimal process parameters for fabricating functionally gradient WC-Co composites is Time=240min, Temperature=1320℃, Volume fraction of methane=1.2vol.%, and flow rate of mixed gases=8L/min. Upon the carburization, WC grains in fine-grained WC-Co hardmetals have a tendency to grow up, but are still at the fine grade.The performance of gradient ultrafine cemented carbide without eta-phase was studied. The results show that, during the fabrication of gradient ultrafine cemented carbide, the test bar can generate different degree of deformation and the influence of process parameters on the deformation has no obvious regularity.After carburizing heat treatment,the magnetic saturation of specimen increase and magnetic coercivity decrease. The hardness of gradient cemented carbide samples along the cross section of the radial appear graded distribution,the hardness on the surface of the specimen is significantly higher than sintering state cemented carbide.The residual stress on the sintered surface of the specimens decrease and the tensile stress transform into compressive stress.The influence of cobalt content and WC grain size on the gradient structure was studied. The results show that, during the fabrication of gradient ultrafine cemented carbide, 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. The higher cobalt content and larger WC grain size, the easier to obtain better thickness and amplitude of the gradients.That is to say,when two fully sintered specimens have similar WC grain sizes but different Co contents, the higher cobalt content,the larger thickness and amplitude of the gradients;In the case that the two specimens have similar Co contents but different WC grain sizes, the larger WC grain size, the larger thickness and amplitude of the gradients.