Influences Of Ultrafine Powder Characteristics And Wet-milling Conditions On Properties And Microstructure Of WC-Co Cemented Carbide

In this work, ultrafine WC-12wt.%Co composite powder was synthesized via spray-drying and direct reduction and carburization process in rotary furnace by using ammonium metatungstate, cobalt ni-trate and glucose as initiative materials. Properties of the composite powder were studied. By using the prepared WC-12wt.%Co composite powder as raw material, Cr3C2, VC, La2O3as additives, after roller ball-milling for48hours, four alloys with different composition were prepared by sintering-HIP. Influences of Cr3C2and VC on the micro-structure and properties of these alloys were investigated. By using the conventional ultrafine WC/Co mixing powder and the prepared WC-12wt.%Co composite powder as two different raw materials, ten different alloys with the same composition were prepared by altering wet milling conditions including the roller wet-milling and the stirring wet-milling, then influences of wet milling conditions on properties and microstruc-ture of alloys was investigated. The main results were as following:1. Through spray-drying and direct reduction and carburization process in rotary furnace, the ultrafine WC-12wt.%Co composite pow-der can be obtained with high-purity and accurately controlled chemical composition, WC particles and Co particles in the composite powder were combined together homogeneously. Perhaps the reaction tempera-ture of direct reduction and carburization was too high, so there existed many polycrystalline WC particles in the composite powder.2. There existed large amount of platelet WC grains in the alloys which were prepared by using the composite powder which was treated by roller ball-milling for48hours beforehand. Cr3C2, VC had the ability to inhibit WC grain growth and influence the growth orientation of the WC grains. Furthermore, the combination of Cr3C2/VC transformed the WC grain morphology from truncated triangle prism to triangular prism structure, and prompted the forming of WC grain growth steps when the amount of Cr3C2is not enough. With increasing the amount of additives, the magnetic saturation induction of the alloys reduced but magnetic co-ercive force increased. The addition of Cr3C2and VC increased the hard- ness but reduced the fracture toughness of the alloy. Both the transverse rupture strength and the fracture toughness of the alloy increased with increasing the amount of ultrafine platelet WC grains.3. When the alloys were prepard by using the ultrafine WC/Co mix-ing powder as raw material, extending the wet-milling time could not re-fine WC grain size of the alloy, the fracture toughness of alloy increased a little but the hardness of alloy reduced a little with the prolongation of wet-milling time. Both the relative density and the transverse rupture strength of alloy reached the highest level when the wet-milling time was60h. Compared with the roller wet-milling, the alloy prepared by the stirring wet-milling had higher density, transverse rupture strength and the fracture toughness, but the hardness was lower and the WC grain size was coarser.4. When the alloys were prepard by using the WC-12wt.%Co composite powder as raw material, extending the wet-milling time had no influence on the grain size and grain distribution of alloy, the distribution uniformity of Co binder in the alloy increased firstly and then decreased with the prolongation of wet-milling time.The transverse rupture strength of alloy reached the highest level when the wet-milling time was48h, up to3679MPa. The hardness of alloy was little changed, around1680HV30. The existence of large amounts of ultrafine platelet WC grains provided benefits to the hardness and the fracture toughness of the alloy. Compared with the roller wet-milling, the alloy prepared by the stirring wet-milling had finer WC grain size for a great degree, higher density and hardness, but the transverse rupture strength and the fracture tough-ness were lower.