The main components of cemented carbide balls are a highly hard and wear-resistant metal carbide (usually tungsten carbide WC) and a metal binder (usually cobalt Co). The structure can be understood as: hard tungsten carbide particles are encapsulated and bonded by the relatively soft metal cobalt, forming an extremely hard yet moderately tough composite material.
I. Main Components of Tungsten Carbide Balls
Tungsten carbide balls are not composed of a single metal, but rather a two-phase composite material.
1. Hard Phase - Tungsten Carbide (WC)
Proportion: Typically 70% to 97% of the total volume, it serves as the alloy's skeleton and main body.
Function: Provides extremely high hardness, wear resistance, and thermal stability. Tungsten carbide's hardness is much higher than that of steel and approaches that of diamond, enabling tungsten carbide balls to withstand intense friction and wear. Other Carbides: Titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), etc. may be added to cemented carbide for certain special applications to improve its red hardness (ability to maintain hardness at high temperatures) and corrosion resistance.
2. Binder Phase - Cobalt (Co)
Composition: Typically 3% to 30% of the total volume, it acts as the alloy's "binder."
Function:
Binding: During the sintering process, the molten cobalt metal infiltrates and envelops the tungsten carbide particles, firmly bonding them together.
Providing Toughness: Pure tungsten carbide is very brittle. The addition of cobalt significantly improves the material's toughness and impact resistance, making it less prone to brittleness.
Other Binders: In certain applications where corrosion resistance is particularly important, nickel (Ni) or iron-nickel (Fe-Ni) alloys may be used as binders in place of cobalt.
Relationship between Composition and Performance:
Lower cobalt content increases the hardness and wear resistance of the cemented carbide, but reduces toughness.
A higher cobalt content improves the toughness of the cemented carbide, but also reduces its hardness and wear resistance.
Therefore, the performance of tungsten carbide balls is customized by adjusting the cobalt ratio depending on the application (for example, precision grinding or high-pressure valve balls).
II. Microstructure of Tungsten Carbide Balls
The typical microstructure of cemented carbide is a two-phase composite.
1. Structural Characteristics: The microstructure consists of a polycrystalline tungsten carbide phase and a continuously distributed cobalt phase.
2. Formation Process: During sintering, the binder phase, cobalt, melts to form a liquid phase. Through a dissolution-reprecipitation mechanism, the tungsten carbide particles coarsen and become densely packed. After final solidification, the cobalt phase forms a continuous film that encapsulates and firmly bonds the tungsten carbide grains.
3. Phase Distribution: The tungsten carbide grains are mostly not in direct contact with each other, but are primarily connected by a thin film of cobalt. This structure achieves an organic combination of high hardness and high toughness phases at the microscale.
III. Key Properties of Tungsten Carbide Balls (Determined by Composition and Structure)
1. Extremely High Hardness: HRA can reach 90-93, significantly higher than hardened steel (approximately HRC 60-65).
2. Extremely High Wear Resistance: Service life is tens or even hundreds of times longer than that of steel balls.
3. High Compressive Strength: Able to withstand significant pressure without deformation.
4. Adequate Toughness: Compared to completely brittle materials like ceramics, the cobalt binder phase imparts a certain degree of resistance to impact and bending.
5. Good Chemical Stability: Excellent resistance to acids, alkalis, and oxidation (especially at low cobalt content).
6. Low Thermal Expansion Coefficient: Minimal dimensional change with temperature, resulting in excellent stability.
IV. Key Applications of Tungsten Carbide Balls
Based on these properties, tungsten carbide balls are widely used in:
1. Precision Grinding Media: Used in equipment such as ball mills and vibratory mills to grind high-hardness materials (such as ceramic powders, magnetic materials, and carbide powders). 2. Core components of industrial valves and pumps: Serves as the valve ball in ball valves, controlling the flow of corrosive, highly abrasive, or high-pressure fluids (e.g., in the oil, natural gas, and chemical industries).
3. Precision bearings: Used in high-speed, high-precision, and corrosion-resistant applications (e.g., precision instruments and medical devices).
4. Measurement and testing: Serves as probes in precision measuring instruments such as coordinate measuring machines and micrometers.
5. Other applications: Armor-piercing projectile cores, sinkers in fishing gear, etc.
