Part 4: Classification and Application Fields of Cemented Carbide
Chapter 10: Classification of Cemented Carbide
As a high-performance material, the classification of cemented carbide (WCCo, etc.) directly determines the precise matching of materials, manufacturing processes and application scenarios. The classification is not only based on composition (WC 70%-95%±1%, Co 5%-30%±1%) and microstructure (grain size 0.5-10 μm±0.01 μm), but also covers performance (hardness HV 800-2000±30, wear resistance <0.06 mm ³ /N · m ± 0.01 mm ³ /N · m) and function (corrosion resistance weight loss <0.1 mg/cm ² ± 0.01 mg/cm ² , conductivity ~10 MS/m±0.1 MS/m). A reasonable classification system provides a theoretical basis and practical guidance for applications in aerospace (tool life >5000 hours ±500 hours), mining (drill impact resistance >10 ⁶ times ±10 ⁵ times) and electronic manufacturing (mold accuracy <1 μm ±0.1 μm).
From a theoretical point of view, the classification of cemented carbide is the product of the combination of materials science and engineering applications. Its core lies in maximizing performance through the optimization of composition and structure. WC provides high hardness and wear resistance as a hard phase, and Co enhances toughness as a bonding phase. The adjustment of the ratio of the two directly affects the mechanical properties and thermal stability of the material. In addition, the grain size of the microstructure is inversely proportional to the hardness through the Hall-Petch relationship. Fine-grained cemented carbide (<2 μm) performs well in high-precision machining, while coarse grains (>5 μm) are more suitable for impact resistance scenarios. Performance parameters such as wear resistance and corrosion resistance reflect the long-term reliability of the material in complex environments, and electrical conductivity provides possibilities for electrical machining processes. Furthermore, grain boundary engineering (such as doping with rare earth elements Ce or Y) can optimize the bonding force between grains and enhance the fatigue resistance of the material. This theory provides a new direction for the design of new cemented carbides.
The classification method has evolved from empirical summary to scientific system. Early classification mainly relied on the ratio of components (such as WC/Co ratio of WCCo), while modern methods combine XRD (X-ray diffraction) and SEM (scanning electron microscopy) techniques to accurately characterize phase composition and grain distribution. International standards (such as ISO 513) further standardize the classification and divide cemented carbide grades according to application fields and performance indicators. In theory, multi-dimensional analysis (such as the comparison between WCCo and WCTiCNi) reveals the effect of TiCN addition on hardness (>HV 1600±30) and high temperature resistance, while the introduction of self-lubricating functions (such as MoS₂ doping ) expands the prospects for special applications. In addition, thermodynamic calculations (such as Gibbs free energy analysis) support phase diagram optimization and guide the design of multiphase cemented carbides (such as WCCoTiCN), reflecting the integration of classification and material genome engineering.
From the application perspective, the scientific nature of the classification directly affects material selection. For example, the requirements for tool life in the aerospace field have driven the development of ultrafine-grained cemented carbides (<1 μm), whose high hardness (>HV 1800) comes from the grain refinement strengthening theory. The mining field requires impact-resistant cemented carbides, and the coarse-grained structure improves fracture toughness (>15 MPa·m ½ ) by reducing dislocation density. In electronic manufacturing, mold accuracy depends on nanoscale grain control, and combined with surface modification technology (such as PVD coating), wear resistance and dimensional stability are further improved. The theoretical support for these application requirements comes from the classification system’s systematic mapping of performance-structure-process.
This chapter starts with the significance and methods of cemented carbide classification, and deeply explores the scientific basis, method evolution and international standards of classification. Through multi-dimensional analysis of composition (WCCo, WCTiCNi), performance (hardness, wear resistance, corrosion resistance) and function (conductivity, self-lubrication), the construction and application of the classification system are systematically explained. This chapter connects Chapter 9 (Multifunctional WCTiCNi, hardness>HV 1600±30), laying the foundation for subsequent application areas (Chapter 11).
10.1 Significance and method of cemented carbide classification
The classification of cemented carbide is the core link of materials science and engineering applications, and runs through the entire process of material research and development, process optimization and practical application. Its significance lies in the fact that through a systematic classification method, the accuracy of material selection can be directly improved (the matching rate can theoretically reach 95%±2%), the production process can be optimized to reduce costs (theoretically 10%±2%), and the accuracy of performance prediction can be improved (theoretically 90%±2%). Classification requires comprehensive consideration of multiple factors, including chemical composition (tungsten carbide WC accounts for 70%-95%±1%), bonding phase (such as cobalt Co or nickel Ni accounts for 5%-30%±1%), microstructural characteristics (such as grain size range 0.5-10 μm±0.01 μm) and functional characteristics (such as theoretical value of friction coefficient <0.2±0.01, theoretical value of resistivity <12 μΩ·cm±0.1 μΩ·cm). A scientific classification system can not only reveal the intrinsic physical and chemical laws of cemented carbide, but also promote the realization of standardized production (the qualified rate can be close to 99%±1%), and support its wide application in cross-industry fields such as aerospace, mining, electronic manufacturing, automobile industry, energy equipment, medical devices and national defense and military. From a theoretical perspective, the classification system optimizes the matching degree between material design and application by establishing a mapping relationship between composition-microstructure-performance, reflecting the latest progress in cutting-edge research fields such as material genome engineering and multi-scale analysis. In addition, the classification also provides important support for sustainable manufacturing, such as effectively responding to the needs of green manufacturing and environmental protection by reducing material waste (theoretical value <2%±0.5%) and improving resource utilization efficiency (theoretical value>98%±1%). At present, with the rapid development of additive manufacturing technology (such as 3D printing cemented carbide) and intelligent production mode (such as AI-assisted design), the classification system needs to further integrate dynamic adjustment mechanisms to adapt to the diverse requirements of emerging processes for material properties and processing conditions, such as potential applications in space exploration or high-precision quantum computing equipment manufacturing.
This section systematically discusses the scientific basis and industrial value of classification, the evolution of classification methods (from composition to function), and international standards and industry practices. It comprehensively explains the significance and methods of classification by combining basic material theory (such as phase diagram analysis, thermodynamic principles), experimental analysis techniques (such as scanning electron microscopy SEM, energy dispersive spectroscopy EDS, theoretical resolution <0.1 μm±0.01 μm) and international standards (such as ISO 513, ASTM B276). For example, WC10Co (theoretical grain size 0.5 μm±0.01 μm) is classified as a cutting tool material due to its high hardness (theoretical value HV 1800±30) and excellent wear resistance (theoretical wear rate 0.05 mm³ / N · m ± 0.01 mm³ / N · m), while WC10Ni (theoretical resistivity 11 μΩ·cm±0.1 μΩ·cm) is suitable for components such as electrical contacts and EDM electrodes due to its conductive properties. This diversity of classification not only reflects the complexity of material properties, but also provides basic support for intelligent manufacturing. For example, data-driven classification models (such as machine learning predictive performance) can improve design efficiency (theoretical value can be increased by 15%±2%), thereby shortening the R&D cycle and reducing testing costs.
10.1.1 Scientific basis, industrial value and application
10.1.1.1 Scientific basis and classification principles
The scientific basis for the classification of cemented carbides is based on a deep understanding of the chemical composition, microstructure and physicochemical properties of the materials. The chemical composition usually includes tungsten carbide WC as a hard phase (theoretical proportion of 70%-95%±1%), cobalt Co or nickel Ni as a bonding phase (theoretical proportion of 5%-30%±1%), and a small amount of functional additives (such as titanium carbide TiC, theoretical proportion of 0%-10%±0.1%). The microstructural characteristics include grain size (theoretical range 0.5-10 μm±0.01 μm), grain boundary density (theoretical value 10 ¹ ⁴ m ⁻ ² ± 10 ¹³ m ⁻ ² ) and phase distribution uniformity, which are characterized by scanning electron microscopy (SEM, theoretical resolution <0.1 μm±0.01 μm) and energy dispersive spectroscopy (EDS). The physicochemical properties include hardness (theoretical range HV 800-2000±30), density (theoretical value 14.5 g/cm ³ ± 0.1 g/cm ³ ), fracture toughness (theoretical range K ₁ c 8-20 MPa·m ¹ / ² ± 0.5), wear resistance (theoretical wear rate <0.06 mm ³ /N · m ± 0.01 mm ³ /N · m) and corrosion resistance (theoretical corrosion current density i_corr<10 ⁻ ⁶ A/cm ² ± 10 ⁻ ⁷ A/cm ² ).
The theoretical basis for classification includes phase diagram analysis and thermodynamic calculations. For example, the WCCo binary phase diagram shows that its liquidus theoretical temperature is about 1300°C±10°C, which reveals the key stage of phase equilibrium and particle rearrangement during sintering; thermodynamics quantifies the stability of each phase through Gibbs free energy (theoretical value ΔG<0 kJ/mol±10 kJ/mol), among which the formation enthalpy of WC (theoretical value ΔH_f~40 kJ/mol±5 kJ/mol) is significantly lower than the oxidation enthalpy of Co (theoretical value ΔH_ox~200 kJ/mol±10 kJ/mol), providing theoretical support for the development of corrosion-resistant materials. In addition, the Hall-Petch relationship shows an inverse relationship between grain size and hardness, with fine grains (theoretical value <2 μm±0.01 μm) theoretically increasing hardness to HV 1800±30, while coarse grains (theoretical value >5 μm±0.01 μm) increase toughness to K₁c > 15 MPa·m¹ / ² ± 0.5 . Performance tests verify theoretical predictions through international standards (such as ASTM G65 wear test and ASTM G59 corrosion test) to ensure the scientificity and consistency of classification. The ultimate goal of classification is to achieve a theoretical performance prediction accuracy of more than 90%±2% and an application matching rate of more than 95%±2%, and lay the foundation for nano-scale cemented carbide (such as theoretical grain value <0.2 μm±0.01 μm) in high-end applications such as high-precision microelectronic molds.
10.1.1.2 Classification Mechanism and Performance Analysis
The performance of cemented carbide comes from the synergistic effect of WC hard phase and Co bonding phase. WC has high chemical bond energy (theoretical value ~700 kJ/mol±10 kJ/mol) and hexagonal crystal structure (Mohs hardness theoretical value>9), which provides excellent hardness and wear resistance for the material; Co uses face-centered cubic (FCC) crystal structure (theoretical elongation 1%±0.1%) as bonding phase, absorbs energy through plastic deformation and enhances the material’s crack resistance. The classification mechanism is based on the following key parameters:
chemical composition
WC is used as the main phase (theoretical proportion 70%-95%±1%), Co or Ni is used as the bonding phase (theoretical proportion 5%-30%±1%), and additives (such as TiC theoretical proportion 5%-10%±0.1%) are used to adjust high temperature performance and corrosion resistance.
Microstructure
The theoretical range of grain size is 0.5-10 μm±0.01 μm, which directly affects the mechanical properties. The theoretical value of grain boundary bonding strength >100 MPa±10 MPa determines fatigue resistance and fracture toughness.
Physical and chemical properties
Theoretical hardness range is HV 800-2000±30, theoretical wear resistance value wear rate <0.06 mm³ / N · m ± 0.01 mm³ / N · m , theoretical corrosion current density i_corr< 10⁻⁶A / cm² ± 10⁻⁷A / cm² .
Phase diagram analysis shows that the WCCo system forms a liquid phase at a theoretical temperature of 1300°C±10°C, promoting particle rearrangement and material densification (theoretical relative density>99.5%±0.1%), while the addition of TiC or TaC can theoretically improve high-temperature stability (theoretical value>1000°C±20°C). Thermodynamic calculations further show that the chemical stability of WC (theoretical formation enthalpy ΔH_f~40 kJ/mol±5 kJ/mol) is superior to the oxidation tendency of Co (theoretical oxidation enthalpy ΔH_ox~200 kJ/mol±10 kJ/mol), providing a theoretical basis for the development of corrosion-resistant cemented carbide. Experimental analysis reveals grain uniformity (theoretical deviation <0.1%±0.02%) through SEM observation (such as WC10Co sample), and EDS analysis confirms the uniformity of Co phase distribution (theoretical deviation <0.1%±0.02%). These microstructural features are closely related to macroscopic properties. Performance test results show that the theoretical wear rate of WC6Co is 0.04 mm ³ /N · m ± 0.01 mm ³ /N · m, making it suitable for high-precision wear-resistant applications, while the theoretical wear rate of WC20Co is 0.08 mm ³ /N · m ± 0.01 mm ³ /N · m, making it more suitable for heavy-duty cutting conditions requiring high toughness.
10.1.1.3 Analysis of influencing factors
The accuracy and practicality of cemented carbide classification are affected by a variety of factors and need to be optimized through systematic analysis. These factors include material composition, microstructure, process parameters, test conditions, external environment and post-processing process, which are discussed in detail below:
Composition deviation
The theoretical fluctuation of the bonding phase Co content of ±1%±0.1% will cause the hardness to change by a theoretical value of ±50. When the TiC content exceeds the theoretical value of 10%±0.1%, the fracture toughness K₁c will theoretically decrease by 10%±2%, while the VC content exceeding 0.5%±0.01% may lead to excessively fine grains (theoretical value <0.3 μm±0.01 μm), increasing the processing brittleness by a theoretical value of 5%±1%. In addition, the TaC content exceeding 5%±0.1% can theoretically increase the high temperature hardness by 10%±2%, but it will also increase the production cost by about 15%±3%.
Grain size
The theoretical range of grain size is 0.5-1 μm±0.01 μm, which can significantly increase hardness (theoretical value>HV 1800±30) and reduce wear rate (theoretical value<0.04 mm³ / N · m ± 0.01 mm³ / N · m). However, when the grain size exceeds 5 μm±0.01 μm, the wear resistance increases by 20%±3% in theory, and the toughness increases (K₁c increases by 15%±2% in theory), but the surface finish decreases in theory (Ra>0.8 μm±0.1 μm). Although nano-grains (theoretical value<0.2 μm±0.01 μm) can increase hardness to a theoretical value>HV 2000±50, abnormal grain growth is prone to occur (theoretical probability>5%±1%), and the sintering temperature needs to be controlled within the theoretical value<1350°C±10°C.
Test conditions
Theoretical load of 10 kg ± 0.1 kg will affect the theoretical value of hardness test deviation < ± 30, when the test speed exceeds 0.1 m/s ± 0.01 m/s, the wear rate will increase by 5% ± 1% in theory, and the ambient humidity will exceed 50% ± 5%, which will cause the corrosion current density i corr to increase by 10% ± 2% in theory, and when the test temperature exceeds 200 ° C ± 10 ° C, the material may undergo thermal softening (theoretical hardness decreases by 5% ± 1%). These conditions need to be standardized to ensure the repeatability of the test results.
Sintering process
The theoretical sintering temperature of 1450°C±10°C can ensure that the material density reaches the theoretical value>99.5%±0.1% and forms a uniform microstructure, but when it exceeds 1500°C±10°C, it will theoretically lead to an increase in phase segregation of 15%±3% and grain growth (theoretical value>10 μm±0.01 μm), thereby reducing the hardness by about 10%±2%. Sintering pressure exceeding 30 MPa±2 MPa can theoretically further improve density (theoretical value>99.8%±0.1%), but it will increase equipment cost by about 5%±1%. Sintering atmosphere (such as Ar or H₂ ) can theoretically reduce oxidation (theoretical value of oxygen content <0.01%±0.001%), otherwise the corrosion resistance will theoretically decrease by 20%±3%.
additive
Cr₃C₂ of 0.5 %±0.01% can improve corrosion resistance by 40%±5% and refine grains (theoretical value <1 μm±0.01 μm), but when it exceeds 1%±0.01%, the fracture toughness K₁c theoretically decreases by 10%±2%; the theoretical addition of VC of 0.2%±0.01% can refine grains (theoretical value <0.5 μm±0.01 μm) and improve hardness by 10%±2%, but when it exceeds 0.5%±0.01%, it will theoretically induce secondary phase precipitation (theoretical value>2%±0.5%) and reduce toughness by about 5%±1%. The theoretical addition of TaC of 2%±0.1% can improve high temperature hardness (theoretical value>HV 1900±30), but it will increase the thermal expansion coefficient (theoretical increase of 5%±1%), which needs to match the base material.
External environment and usage conditions
Operating temperatures exceeding 800°C±20°C theoretically lead to softening of the Co phase (theoretical decrease in hardness by 15%±2%), acidic environments (theoretical pH value <4±0.5) theoretically increase the corrosion current density i_corr by 30%±5%, and the probability of microcrack formation theoretically exceeds 10%±2% when the impact load exceeds 500 J±50 J. These factors require the classification system to take into account service life prediction (theoretical value >5000 hours±500 hours) and potential failure mode analysis.
Post-processing
Grinding can theoretically reduce the surface roughness to Ra<0.2 μm±0.05 μm, but it will introduce residual stress (theoretical value>200 MPa±20 MPa); coating (such as TiN) can theoretically improve wear resistance by 30%±5%, but the probability of peeling under high load is theoretically more than 5%±1%; heat treatment (such as low-temperature annealing at 600°C±10°C) can theoretically relieve stress by 20%±3%, but the hardness is theoretically slightly reduced by <5%±1%.
For example, WC10Co is classified from high hardness to medium hardness because its grain size theoretically exceeds 5 μm±0.01 μm, and its hardness theoretically drops to HV 1500±30; WC10Ni with a theoretical amount of 15%±0.1% TiC added is classified as wear-resistant and conductive rather than high toughness because of its insufficient fracture toughness (theoretical value K₁c ~ 8 MPa·m¹ / ² ± 0.5 ). The comprehensive analysis of these factors ensures the scientificity and practicality of the classification system, enabling it to adapt to complex working conditions and diversified market demands.
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