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S. Wawrzik, C. Buchegger, M. Wetzel, W. Lengauer:
"Rim-Nitrided WC Powder: Preparation, Properties and Use for Hardmetals";
Talk: 18. Plansee Seminar 2013, Reutte; 06-03-2013 - 06-07-2013; in: "Proceedings", (2013), 10 pages.

Nitrogen uptake of commercial WC powders of different grain size was studied by high-pressure
nitridation up to 150bar N2 and temperatures up to 1350°C. The nitrided powders were characterised by
XRD, chemical analysis and TEM. Interestingly, it was found that a perceptible amount of nitrogen
dissolves in WC. As the diffusion rate of N in WC is extremely slow, nitridation occurs in the outermost
rim of the WC particles. Upon appropriate nitridation conditions the powders are even purified with
respect to the oxygen level.
Sintering experiments were performed with these powders for a possible use in the preparation of
hardmetals. It turned out that nitrogen can retard low temperature grain growth and thus hardmetals of
reduced grain size and narrow grain-size distribution can be obtained. Mass-spectrometric delubing
experiments (EGA-MS) showed that the powders lose nitrogen (and CO) upon sintering. The nitrogen
loss of finer powders starts at around 800°C and ends when the eutectic temperature is reached.
Coarser powder lose nitrogen at around 1200-1250°C. Thus, porosity is avoided as compared to the use
of homogeneous W(C,N) powders. The CO evolution of nitride powders is reduced due to a lower
oxygen content after nitridation.

Nitrogen uptake of commercial WC powders of different grain size was studied by high-pressure
nitridation up to 150bar N2 and temperatures up to 1350°C. The nitrided powders were characterised by
XRD, chemical analysis and TEM. Interestingly, it was found that a perceptible amount of nitrogen
dissolves in WC. As the diffusion rate of N in WC is extremely slow, nitridation occurs in the outermost
rim of the WC particles. Upon appropriate nitridation conditions the powders are even purified with
respect to the oxygen level.
Sintering experiments were performed with these powders for a possible use in the preparation of
hardmetals. It turned out that nitrogen can retard low temperature grain growth and thus hardmetals of
reduced grain size and narrow grain-size distribution can be obtained. Mass-spectrometric delubing
experiments (EGA-MS) showed that the powders lose nitrogen (and CO) upon sintering. The nitrogen
loss of finer powders starts at around 800°C and ends when the eutectic temperature is reached.
Coarser powder lose nitrogen at around 1200-1250°C. Thus, porosity is avoided as compared to the use
of homogeneous W(C,N) powders. The CO evolution of nitride powders is reduced due to a lower
oxygen content after nitridation.

hardmetal, cemented carbides, nitrogen, nitridation, grain growth, grain size