**Author details**

50 Tungsten Carbide – Processing and Applications

microstructure.

from the WC phase.

**7. Conclusions** 

findings:

and Chaim and Reinharz [Chaim R and Reinharz Bar-Hama, 2010] have suggested, this GB complexion leads to a plastically softened surface layer which can activate rapid atomic diffusion and promote particle rearrangement and creep leading to very low activation energies during sintering. At high temperatures, the 'particle' identity is lost and grain growth rate also increases. The thickness of the recrystallized layer decreases in comparison to the grain size, although the GB is still an active diffusion route until complete densification is achieved. This idea is consistent with our observed kinetic results and the

**Figure 23.** XRD of the samples interrupted at different temperatures. The WO3 phase is seen at almost all low temperatures, while the final compact only shows WC and graphite. All the primary peaks are

The SPS behaviour of *n*-WC appears to be a complex process involving size effects, field effects, chemical reactions and anomalously rapid diffusion. Experimental observations described in this work show evidence of planar defects, possible GB reconstruction and agglomeration that can contribute to the lowering of the sintering activation energy. In our analysis and from the current volume of literature cited to support our view, it is clear that the fundamental aspects of sintering pertaining to nano particles particularly in the presence of an electromagnetic field can be largely different, for which an exact theory is yet to be developed. A few significant results of this work are given below to summarize our A.K. Nanda Kumar *Dept. of Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio, USACentre for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo, Japan* 

Kazuya Kurokawa *Centre for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo, Japan* 

### **Acknowledgement**

This work was carried out while AKNK was a foreign researcher at Hokkaido University, Japan. The project was partly funded by the Ohtaseiki Co., Ltd., Japan. AKNK also wishes to express his deep sense of gratitude to Prof. K Kurokawa, for having introduced him to this work and for providing financial support during his stay in Japan. Profs. A Yamauchi and N

Sakaguchi are also gratefully acknowledged for their timely help with the SPS and TEM work and also for many discussions during the course of this work.

Spark Plasma Sintering of Ultrafine WC Powders: A Combined Kinetic and Microstructural Study 53

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