Tungsten Carbide Powder (WC) Description
Tungsten carbide powder (WC) is the main raw material for manufacturing hard alloys, with the chemical formula WC. Tungsten carbide has a metallic luster and its hardness is similar to diamond, being a good conductor of both electricity and heat.
Tungsten carbide is insoluble in water, hydrochloric acid and sulfuric acid, but easily dissolves in a mixed acid of nitric acid and hydrofluoric acid. Pure tungsten carbide is brittle, but the addition of small amounts of metals such as titanium or cobalt can reduce its brittleness. When used in steel cutting tools, tungsten carbide is often mixed with titanium carbide (TiC), tantalum carbide (TaC) or their mixtures to improve impact resistance. Tungsten carbide is chemically stable.
The appearance of tungsten carbide powder is gray, and its color changes from dark to light as the particle size increases. It can dissolve in various carbides, especially showing high solubility in titanium carbide to form TiC-WC solid solutions.
Benefits of Adding Cobalt (Co) and Chromium (Cr) Elements to Tungsten Carbide (WC) Powder
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Benefits of Adding Cobalt (Co)
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Binding Phase Effect:
Cobalt, as the primary binding phase, significantly improves the flexural strength (up to 2000-4000 MPa) and toughness of WC-Co cemented carbide while reducing brittleness.
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Promotion of Densification:
Due to its relatively low melting point (1495°C), cobalt forms a liquid phase during sintering, facilitating the rearrangement of WC particles and increasing density (up to over 99%).
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Balance of Wear Resistance:
The cobalt content (typically 3-20 wt%) can adjust the balance between hardness (HRA 88-93) and wear resistance, making it suitable for cutting tools, molds, etc.
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Limitation in Corrosion Resistance:
Cobalt is prone to corrosion in acidic environments, so WC-Co alloys are not suitable for highly corrosive conditions.
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Benefits of Adding Chromium (Cr)
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Enhanced Oxidation Resistance:
Chromium forms a dense Cr?O? oxide film on the surface, significantly improving the alloy’s high-temperature oxidation resistance (up to over 800°C).
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Improved Corrosion Resistance:
Particularly suitable for acidic/alkaline environments (e.g., chemical seals), it can partially replace more expensive nickel (Ni)-based binders.
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Grain Refinement:
Chromium inhibits the growth of WC grains during sintering, refining the microstructure and enhancing hardness (HV 1500-2000) and wear resistance.
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Modification of Binding Phase:
In the WC-Co-Cr system, chromium improves the uniform distribution of the cobalt phase, reducing localized stress concentration.
Synergistic Effect of Cobalt and Chromium
In the WC-Co-Cr ternary system, the Co+Cr composite binding phase combines high toughness (contributed by Co) and corrosion resistance (contributed by Cr), making it suitable for marine environments or chemical pump/valve components. For example:
