Density is a fundamental physical property of cemented carbides. A consistent density indicates a uniform distribution of the carbide phase and the binder metal within the material. To control the density, precise weighing of raw materials is crucial during the powder mixing stage. The sintering process also has a significant impact on density. Over - sintering may cause excessive shrinkage and changes in density, while under - sintering can lead to a lower - than - expected density due to incomplete densification. Regularly measuring the density of finished products using methods such as the Archimedes' principle helps ensure that the density falls within the specified range, which is typically between 9 - 15 g/cm³ depending on the composition of the cemented carbide.
Coercivity reflects the ability of a magnetic material to resist demagnetization. In cemented carbides, it is related to the grain size and distribution of the carbide phase and the binder metal. A proper coercivity value indicates a well - dispersed and fine - grained structure. To control coercivity, factors such as the particle size of the raw powders, the milling process, and the sintering conditions need to be carefully managed. During powder milling, the milling time and intensity should be optimized to achieve the desired particle size and distribution. The sintering temperature and time also play a vital role in determining the coercivity. By closely monitoring and adjusting these parameters, the coercivity of the cemented carbide can be maintained within the required range.
Magnetic saturation is an important magnetic property that is related to the amount of binder metal in the cemented carbide. It provides information about the uniformity of the binder phase distribution. To ensure the correct magnetic saturation value, the proportion of the binder metal (usually cobalt) added during the powder mixing process must be accurately controlled. Any deviation in the binder content can lead to changes in magnetic saturation. Additionally, the sintering process should be carried out under proper conditions to prevent the formation of abnormal phases that could affect the magnetic properties. Regular magnetic saturation measurements using appropriate magnetic testing equipment can help detect any variations and allow for timely adjustments.
Hardness is one of the most critical properties of cemented carbides, as it directly affects the material's wear resistance and cutting performance. The hardness of cemented carbides is mainly determined by the carbide phase and its grain size, as well as the amount and distribution of the binder metal. To control hardness, high - quality carbide powders with appropriate particle sizes should be selected. The milling process should be designed to break down the agglomerates and ensure a homogeneous mixture. During sintering, the temperature and time should be carefully adjusted to achieve the desired grain growth and phase transformation. Post - sintering heat treatment can also be used to fine - tune the hardness. Regular hardness testing using methods such as the Rockwell or Vickers hardness tests helps ensure that the hardness meets the application requirements.
Porosity refers to the presence of voids or pores within the cemented carbide. High porosity can significantly reduce the mechanical properties and corrosion resistance of the material. To control porosity, the powder compaction process is of utmost importance. Adequate pressure should be applied during compaction to ensure a high - density green body. The sintering atmosphere also affects porosity. A proper sintering atmosphere, such as a vacuum or a controlled gas environment, can prevent the formation of pores caused by gas entrapment or oxidation. In addition, the particle size and shape of the raw powders can influence porosity. Fine and spherical powders tend to result in lower porosity. Regular inspection of the porosity using techniques such as metallographic analysis or X - ray tomography helps detect and address any porosity issues.
The presence of cobalt pools in cemented carbides is an undesirable phenomenon. Cobalt pools are areas where the binder metal (cobalt) has agglomerated, which can lead to a non - uniform distribution of properties and reduced performance. To avoid cobalt pools, the powder mixing process should be thorough to ensure a homogeneous distribution of the binder metal. The milling time and intensity should be sufficient to break up any cobalt agglomerates. During sintering, the heating rate and temperature should be carefully controlled to prevent the excessive movement and agglomeration of the binder metal. Microstructural analysis using techniques such as scanning electron microscopy (SEM) can be used to detect the presence of cobalt pools and take corrective measures.
Free carbon or graphite in cemented carbides can have a negative impact on the material's properties. It can cause brittleness and reduce the strength of the material. To control free carbon, the carbon content in the raw materials should be accurately measured and adjusted. The sintering process should be carried out in an environment that minimizes the loss or gain of carbon. For example, a proper sintering atmosphere can prevent carbon from reacting with other elements or escaping from the material. Chemical analysis techniques, such as combustion analysis, can be used to determine the carbon content and ensure that it is within the acceptable range.
The phase composition of cemented carbides is crucial for their performance. The correct balance between the carbide phase (such as WC) and the binder phase (usually Co) is essential. To control the phase composition, the raw materials' purity and stoichiometry should be carefully controlled. The milling and sintering processes should be optimized to ensure the proper formation and transformation of phases. X - ray diffraction (XRD) analysis is a commonly used technique to determine the phase composition. By regularly analyzing the phase composition, any deviations from the desired phase structure can be detected early, and appropriate adjustments can be made to the manufacturing process.
Transverse rupture strength is a measure of the material's ability to withstand bending stress. It is an important property for applications where the cemented carbide is subjected to high - load conditions. To control the transverse rupture strength, factors such as the grain size, porosity, and phase composition need to be managed. Fine - grained structures with low porosity generally exhibit higher transverse rupture strength. The sintering process should be optimized to achieve a dense and homogeneous structure. Additionally, the surface finish of the material can also affect the transverse rupture strength. Any surface defects or cracks can act as stress concentrators and reduce the strength. Regular testing of the transverse rupture strength using a three - point or four - point bending test helps ensure that the material meets the strength requirements.
In summary, controlling the quality of cemented carbides requires a comprehensive approach that involves careful management of raw materials, precise control of manufacturing processes, and regular testing and analysis of key properties. By closely monitoring and adjusting these parameters, high - quality cemented carbides with consistent performance can be produced.
