Refers to a sintered composite material composed of refractory metal carbides and metallic binders. Among the metal carbides currently in use, tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), and niobium carbide (NbC) are the most common components. Cobalt metal is widely used as a binder in the production of cemented carbide; other metallic binders such as nickel (Ni) and iron (Fe) can also be used for specific applications.
Refers to the ratio of the mass of a material to its volume, including the volume of pores within the material. Also known as specific gravity. The density of tungsten carbide (WC) is 15.7 g/cm³, and the density of cobalt (Co) is 8.9 g/cm³. Therefore, as the cobalt (Co) content in tungsten-cobalt alloy (WC-Co) decreases, the overall density increases. The density of titanium carbide (TiC) is much lower than that of tungsten carbide, at only 4.9 g/cm³. Thus, adding TiC or other lower-density components will reduce the overall density. An increase in porosity within the material will lead to a decrease in density, given a constant chemical composition. Density is measured using the water displacement method (Archimedes’ principle).
Refers to the ability of a material to resist plastic deformation. Vickers hardness (HV) is widely used internationally. This hardness measurement method involves penetrating the surface of a sample with a diamond under a specific load and measuring the size of the indentation to obtain the hardness value. Rockwell hardness (HRA) is another commonly used hardness measurement method. It measures hardness by the depth of penetration of a standard diamond cone. Both Vickers and Rockwell hardness measurement methods can be used to measure the hardness of cemented carbide, and the values can be converted between the two.
A sample is supported as a simply supported beam on two points, and a load is applied at the centerline between the two points until the sample fractures. The value is calculated using the bending formula based on the load required to fracture the sample and the cross-sectional area of the sample. Also known as transverse rupture strength or flexural strength. In tungsten-cobalt alloy (WC-Co), flexural strength increases with the cobalt (Co) content, but after reaching a maximum value at around 15% cobalt (Co) content, it starts to decrease. The flexural strength is taken as the average value of several measurements. This value can vary with changes in the sample’s geometry, surface condition (smoothness), internal stress, and internal defects. Therefore, flexural strength is just one method of measuring strength and should not be the sole criterion for material selection.
Cemented carbide is made using powder metallurgy processes, including pressing and sintering. Due to the nature of these processes, trace residual porosity may exist in the metallographic structure of the product. The volume of residual porosity is evaluated using a comparative procedure with charts showing pore size ranges and distributions. A-type: Less than 10 μm. B-type: Between 10 μm and 25 μm. Reducing porosity can effectively improve the overall performance of the product. Pressure sintering is an effective method to reduce porosity.
Refers to the insufficient carbon content in cemented carbide after sintering. When decarburization occurs, the structure changes from WC-Co to W2CCo2 or W3CCo3. The ideal carbon content in tungsten carbide (WC) is 6.13% by weight. When the carbon content is too low, there will be a noticeable decarburized structure in the product. Decarburization significantly reduces the strength of tungsten carbide cemented carbide, making it more brittle.
Refers to the excessive carbon content in cemented carbide after sintering. The ideal carbon content in tungsten carbide (WC) is 6.13% by weight. When the carbon content is too high, there will be a noticeable carburized structure in the product, with excess free carbon. Free carbon significantly reduces the strength and wear resistance of tungsten carbide cemented carbide. In phase detection, C-type pores indicate the degree of carburization.
Coercive force is the residual magnetism measured after magnetizing the magnetic material in cemented carbide to saturation and then demagnetizing it. There is a direct relationship between the average grain size of the carbide phase and the coercive force: the finer the average grain size of the magnetic phase, the higher the coercive force value.
Cobalt (Co) is magnetic, while tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), and vanadium carbide (VC) are non-magnetic. Therefore, by measuring the magnetic saturation value of cobalt in a material and comparing it to the corresponding value of pure cobalt, the level of alloying in the cobalt binder phase can be determined, as magnetic saturation is affected by alloying elements. Any changes in the binder phase can be measured. This method can be used to determine deviations from the ideal carbon content, as carbon plays an important role in composition control. Low magnetic saturation values indicate the possible presence of low carbon content and decarburization. High magnetic saturation values indicate the presence of free carbon and carburization.
After sintering with metallic cobalt (Co) binder and tungsten carbide, excess cobalt may form, a phenomenon known as “cobalt pool.” This is mainly due to low sintering temperatures, insufficient material forming density, or pores being filled with cobalt during HIP (Hot Isostatic Pressing) treatment. The size of the cobalt pool is determined by comparing metallographic images. The presence of cobalt pools in cemented carbide may affect the material’s wear resistance and strength.
CYC is equipped with all the testing equipment for the above-mentioned properties and indicators of cemented carbide. Each batch of products undergoes these tests to ensure they meet quality standards before being delivered to customers.
