Tungsten carbide oxidation presents a significant challenge limiting its high-temperature applications. This hard, wear-resistant material excels in cutting tools, dies, and wear parts, but exposure to oxygen at elevated temperatures triggers degradation.

(tungsten carbide oxidation)

The oxidation process begins noticeably around 400-500°C. Atmospheric oxygen reacts chemically with the tungsten carbide grains. The primary reaction is WC + 5/2 O2 → WO3 + CO2. This forms tungsten trioxide (WO3), a voluminous, brittle oxide, and carbon dioxide gas.

This reaction has detrimental consequences. The formation of WO3 creates significant internal stresses due to its larger molar volume compared to WC. This leads to cracking and spallation of the oxide layer. Crucially, the escaping CO2 gas creates pores and voids within the material structure. This combination of oxide formation and gas evolution causes severe material loss, surface pitting, and a catastrophic disintegration phenomenon known as “pest oxidation” at certain temperatures, destroying structural integrity.

Oxidation significantly accelerates tool wear mechanisms like flank wear and crater wear in machining applications. It reduces hardness and strength, leading to premature failure. The rate increases dramatically with rising temperature.

(tungsten carbide oxidation)

Mitigation strategies are essential. Applying protective coatings (like Al2O3, TiAlN, TiCN) creates a barrier against oxygen diffusion. Alloying with elements forming stable oxides (e.g., chromium) can improve inherent oxidation resistance. Careful control of the cobalt binder phase chemistry and microstructure also plays a role. Limiting operating temperatures below the critical oxidation threshold remains the simplest, though often impractical, defense. Understanding and managing tungsten carbide oxidation is vital for extending component life in demanding environments.
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