**5. References**


[10] Gao L, Kear B (1995) Low Temperature Carburization of High Surface Area Tungsten Powders. Nanostruct. Mater. 5: 555-569.

18 Tungsten Carbide – Processing and Applications

 Availability of theoretically explained backgrounds for governing the reaction temperature and velocity and component conversion completeness, which provide the possibility of obtaining high quality products of the preset structure at optimum terms; Low requirements to the initial mixture quality since partial self-purification of SHS

products from admixtures takes place during the combustion process;

Possibility of industrial production of nanosized materials.

nanosized materials is commercially important.

I. Borovinskaya, T. Ignatieva and V. Vershinnikov

**Author details** 

**Acknowledgement** 

**5. References** 

241-255.

p.

comments and suggestions.

Mater. 13: 281-296.

of Materials. 97 p.

Tungsten Carbides. J. de Phys. IV. 5: 967-974

Hertfordshire UK: Int.Carbide data. p.88

and Silicides. New York: The MacMillan Company. 447 p.

Simple equipment using various approaches of physical influence on the substance;

*Institute of Structural Macrokinetics and Materials Science, Chernogolovka Moscow Russian* 

The authors wish to express their deep thanks to Academician A.G.Merzhanov for useful

[1] Rafaniello W (1997) Critical powder characteristics. In: Weimer A, editor. Carbide, nitride, and boride materials synthesis and processing. London: Chapman æ Hall. 671

[2] Schubert W, Bock A, Lux B (1995) General aspects and limits of conventional ultrafine WC powder manufacture and hard metal production. Int. J. Refract. Metals Hard

[3] Jia K, Fischer T, Gallois B (1998) Microstructure, hardness and toughness of nanostructured and conventional WC-Co composite. Nanostruct. Mater. 10: 875-891. [4] Spriggs G (1995) A history of fine grained hard metal. Int. J. Refract. Met. Hard Mater. 13:

[5] Cottrell A (1995) Chemical bonding in transition metal carbides. London: The Institute

[6] Tägtström P, Högberg H, Jannson U, Carlsson J.-O (1995) Low Pressure CVD of

[7] Schwartzkopf P, Kieffer R (1953) Refractory Hard Metals: Borides, Carbides, Nitrides

[9] Brookes K (1992) World Directory and Handbook of Hard Metals and Hard Materials.

[8] Rieck G (1967) Tungsten and its Compounds. Oxford: Pergamon Press. 138 p.

Nowadays, the number of ultra-dispersed materials produced in industry is restricted. Development of industrial production technologies and widening of application fields of

	- [28] Borovinskaya I, Vishnyakova G, Savenkova L (1992) Мorphological features of SHS boron and aluminum nitride powders. Int. J. of SHS. 1: 560-565.

**Chapter 2** 

© 2012 Kumar and Kurokawa, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

© 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

**Spark Plasma Sintering of Ultrafine WC Powders:** 

Nano grained cemented tungsten carbide (*n*-WC) is currently being researched for many potential applications in manufacturing processes. An example is the near net shape manufacturing of aspheric glass lenses. With the advent of optical technology and electrooptic systems, conventional spherical lenses are now being replaced by aspheric lenses of smaller dimensions and lower curvatures to be accommodated inside flat cellular phones and DVD readers. A cost effective method of fabricating such small aspheric lenses is by molding the glass gob in a suitable preform or mold at temperatures near the glass transition temperature (*Tg*). WC-based cemented carbides are a natural choice for the mold because of their high hot hardness and low coefficient of thermal expansion, CTE (which is compliant with the CTE of glass). A major issue in this near net shape fabrication method is that the surface finish of the carbide mold should be extremely smooth as otherwise the glass component will also reproduce the surface roughness of the mold. This eventually leads to aberration of the lens and a loss of precision, consequently necessitating the need for an extra grinding or polishing step after the manufacturing process. Ultra-fine grained carbides, owing to their small grain size, can be polished to extreme smoothness of the order of 2-3 nm or lesser. To facilitate the lens' release from the mold, usually Ir or Re coatings are applied on the mold surface. Generally, this arrangement works well for near net shape mass production of small aspheric lenses and is commonly used in lens manufacturing industries. Another instance where *n*-WC assumes commercial importance is in the micromachining industry where often extremely small holes have to be drilled into hard substrates. The drill-bit in such applications is made of WC with a very small curvature at its tip which is possible only if the grain size is in the nano-metric range. Larger grains lead to blunting when the tip undergoes brittle intergranular fracture resulting in chipping off a

**A Combined Kinetic and Microstructural Study** 

A.K. Nanda Kumar and Kazuya Kurokawa

Additional information is available at the end of the chapter

large chunk of the material from the drill tip.

http://dx.doi.org/10.5772/55291

**1. Introduction** 

