**6. References**

396 Sintering of Ceramics – New Emerging Techniques

Fig. 22. SEM micrograph of the AL5 sample sintered under HPHT.

Fig. 23. SEM micrograph of the AL7 sample sintered under HPHT.

the properties of the cemented carbide investigated.

In this chapter the cemented carbide (WC10wt.%Co) powder doped with different rare-earth elements (La2O3 and CeO2) sintered under HPHT conditions was investigated. The method used can be an alternative for WC10wt.%Co dense pellets processing. High final densities near theoretical density have been obtained. It was also found that the incorporation of rare-earth elements positively influenced the physical and mechanical properties of the cemented carbide. These properties include increased densification, increase in coercive field, axial compressive strength, axial elasticity, microhardness and wear resistance. This behavior is due to the addition of rare-earth elements leads to decreased porosity of the cemented carbide. Moreover, it was observed that the lanthanum oxide (La2O3) was more effective in improving

**4. Conclusion** 

Arbilla, G.; Corrêa, S.M. & Carvalho, M.S. (1996). *Ciência Hoje*, Vol. 21,No. 122


**Part 5** 

**Conventional Sintering** 


**Part 5** 

**Conventional Sintering** 

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North, B.; Pfouts, W.R. & Greenfield, M.S. (1991). Pressure Sinter and HIP on Cemented

Pan, Q. (1993). Effects of Rare-Earth Oxide on the Properties of WC-Co Cemented Carbide,

Ramalho, A.M. (1998). A Influência da Construção e dos Materiais sobre o Estado de

Rodrigues, M.F.; Bobrovnitchii, G.S.; Quintanilha, R.; Cândido, R.; Silva, G. & Figueira, M.

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Silva, A.G.P. (1996). Study on Sintering and Grain Growth of WC-Based Hard Metals,

Thümmler, F. & Oberacker, R. (1993). *Introduction to Powder Metallurgy*, The Institute of

White, C. (1998). History of Powder Metallurgy, In: *Handbook of Powder Metal Technologies* 

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**18** 

*Brazil* 

**Mechanisms of Microstructure** 

Adriana Scoton Antonio Chinelatto1, Elíria Maria de Jesus Agnolon Pallone2,

**Control in Conventional Sintering** 

Ana Maria de Souza1, Milena Kowalczuk Manosso1, Adilson Luiz Chinelatto1 and Roberto Tomasi3

*2Department of Basic Sciences – FZEA - São Paulo University* 

*1Department of Materials Engineering - State University of Ponta Grossa* 

*3Department of Materials Engineering - Federal University of São Carlos* 

The manner and mechanisms involved on the sintering process are essential investigation to achieve the required microstructure and final properties in solids. During the conventional sintering of a compacted powder, densification and grain growth occur simultaneously through atomic diffusion mechanisms. Many researchers have been working on reducing the grain size below 1 μm aiming to improve some properties, such as strength, toughness and wear resistance in ceramics (Greer, 1998; Inoue & Masumoto, 1993; Morris, 1998). In order to obtain ultra-fine ceramic microstructures, nanocrystalline powders can be used. Although the sinterability of nanoparticles is superior to that of fine particles due to the higher sintering stress, densification of these powders is often accompanied by grain growth

Hot pressing sintering (He & Ma, 2000; Porat et al., 1996), spark plasma sintering (Gao et al., 2000; Chakravarty et al., 2008) or pulse electric current sintering (Zhou et al., 2004) are typical techniques employed to produce nanostructured ceramics. However, many of these techniques are not economically viable depending on the use of the final product. Thus, conventional pressureless sintering is still a more attractive sintering method to produce ceramic products, mainly due to its simplicity and cost compared to other methods. In the conventional pressureless sintering, a controlled grain size with high densification could be achieved by adequate control procedures of the heating curve — herein defined as the

One hypothesis to the heating curve control can be achieved by improving the narrowing of grain size distribution in a pre-densification sintering stage followed by a final densification stage namely at a maximum densification rate temperature (Chu et al., 1991; Lin & DeJonghe, 1997a, 1997b). In a thermodynamics point-of-view, another hypothesis is regarded to control the heating schedule at temperature ranging the active grain boundary diffusion. Note, however, that the grain boundary migration is sufficiently sluggish and the

maximization of the final density with minimum grain growth.

**1. Introduction** 

(Suryanarayana, 1995).
