Tribological behavior of hot-pressed boron carbide with oxidation

Abstract

The oxidation behavior at 973–1 273 K and the effect of oxidation on the room-temperature tribological properties of hot-pressed boron carbide ceramic were investigated. Oxidized samples were studied by X-ray diffractometer and scanning electron microscopy. It is demonstrated that the oxidation results in the formation of a thin transparent B₂O₃ film, and the oxide film is severely cracked during cooling due to the thermal expansion mismatch between the oxide film and B₄C substrate. B₂O₃ reacts with moisture in air to form boric acid, which is a kind of solid lubricant. The sliding friction factors of oxidized B₄C pair are about 0.05–0.08, compared to 0.25–0.35 of the as-received B₄C pair. When the oxidation temperature is up to 1 273 K, severe unstability and increase of friction factor are observed. Visual inspection of the wear track reveals that the lubricant film is broken and some debris particles occur on and around the rubbing surfaces, because the friction interface is rough by the severe etching of grain boundaries.

Keywords

oxidation / boron carbide / friction factor / boron oxide / boron acid

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