Preparation And Properties Of Binderless Tungsten Carbide

WC is given a lot of attention due to its excellent hardness and wear resistance,but the poor toughness and difficulty of sintering have limited its application.This problem may be solved when the toughening material ZrO₂ with high temperature stability and a small amount of metal binder were added into WC.In this paper,WC powder?0.53?m?including0.54wt.%Cr₃C₂ and 0.33wt.%VC,and tetragonal polycrystals zirconia?3Y-TZP?powder which containing 3 mol.%Y₂O₃ as the main raw material,Ni as the metal binder were prepared by vacuum sintering/hot pressing sintering+hot isostatic pressing treatment.The effect and mechanism of sintering process and composition on the densification of WC ceramic was investigated.The results show that the density of WC-ZrO₂ composite ceramics is difficult with pressureless sintering.The relative density of WC-4wt.%ZrO₂ sintered at 1800?with vacuum pressureless sintering is only 76.27%and a large amount of carbon-deficient phase W₂C is formed.But the material can be densified by hot pressing sintering at 1600?for 0.5h,and the density of the material can be further enhanced by hot isostatic pressing treatment?1600?*100MPa*2 h?.The existence of ZrO₂ can promote the sintering of materials.When the sintering temperature is raised to 1650?,the WC-2wt.%ZrO₂ composite ceramics is almost densification completely.The density,hardness and fracture toughness is 99.15%,22.5GPa,6.5MPa·m^1/2respectively.Compared with the WC-2wt.%ZrO₂ samples sintered at1600?and treated by hot isostatic pressing,it is found that the effect of hot isostatic pressing treatment is not as obvious as that of increasing sintering temperature.The initial densification of WC-Ni composite ceramics with a small amount of metal binder can be achieved under vacuum sintering.And the dense WC-Ni composite ceramics with complex shapes can be prepared by vacuum sintering+hot isostatic pressing process.The results show that when Ni content is higher than 0.25 wt.%,the basic densification of WC composite ceramics can be realized.With the increase of Ni content,the densification of the material increases and the amount of carbon-deficient W₂C decreases.When Ni content is 1wt.%,there is no carbon-deficient phase.With the increase of Ni content,the hardness decreases gradually,while the fracture toughness increases for the increase of Ni content and densification.The WC-0.5wt.%Ni sintered at 1700?has the best strength and toughness.After hot isostatic pressing,the material is completely compact,the density,hardness and fracture toughness is 100.00%,24.9 GPa and 12.2MPa·m¹/2/2 respectively.And the flexural strength increases with the increase of Ni content.The bending strength of WC-0.5wt.%Ni was the highest which is 749.2MPa,and the main fracture mode was the transgranular fracture of WC particles.For WC-ZrO₂-Ni composite ceramics,the initial densification of WC-ZrO₂-Ni composites can be obtained under vacuum sintering due to the addition of Ni.With the increase of sintering temperature,the density of the material increases continuously.The WC-2wt.%ZrO₂-1wt.%Ni composites processed by vacuum sintering at 1700?were further densified by hot isostatic pressing at 1600?*60MPa*2 h,and the relative density reached99.96%.The high densification of the composites and the existence of ZrO₂ phase increase the fracture toughness and flexural strength of WC composite ceramics.The hardness of WC-2wt.%ZrO₂-1wt.%Ni composites after vacuum sintering at 1700?and hot isostatic pressing can reach 22.4 GPa with fracture toughness of 12.0MPa·m^1/2,and flexural strength of 1101.2 MPa.The fracture mechanism is transgranular fracture of WC matrix and ZrO₂and intergranular fracture of a small amount of ZrO₂ and WC particles.