Peculiarities of vacuum annealing of nanocrystalline WC powders

The effect of vacuum annealing temperature on the phase and chemical composition, particle size, and microstrains of nanocrystalline powders of tungsten carbide WC with particles from 20 to 60 nm in size has been studied using X-ray diffraction and electron microscopy methods. It is established that nanocrystalline WC powders stored in air, contain from 1 to 2 wt.% of impurity oxygen. It is found that vacuum annealing of WC nanopowders at a temperature up to 1400 °C is accompanied by appreciable decarburization and variation in the phase composition due to carbon desorption as a result of interaction with impurity oxygen. Annealing leads to coarsening of powder particles caused by intergrowth of aggregated nanoparticles and to decreasing microstrains.

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► Stored in air nanocrystalline powders of tungsten carbide WC with particles from 20 to 60 nm in size contain from 1 to 2 wt.% of impurity oxygen.
► Vacuum annealing of WC nanopowders at a temperature up to 1400 °C is accompanied by appreciable decarburization and variation in the chemical and phase composition.
► During annealing, the relative loss of carbon is proportional to the content of impurity oxygen which desorbs from WC mainly as carbon oxide.