Liquid-phase sintering microstructures

Wang, C.M., Mitomo, M., and Emoto, H., Microstructure of liquid phase sintered superplastic silicon carbide ceramics , J. Mater. Res. 1997, 12, 3266-70. 

Typical microstructures developed by solid state sintering, liquid phase sintering and firing a porcelain are shown in Fig. 5.20. 

The compacted powder mixtures of these materials are usually liquid phase sintered with Ni or Ni-Co binder metal alloys. The microstracture features a core-and-rim stracture of the hard phase with a molybdenum- and carbon-rich (Ti,Mo)C rim and a titanium- and nitrogen-rich Ti(C,N) core. This microstructure can be made visible in the SEM (Figure 16). The metallurgy of the phase reactions is not... 

Figure 1. Microstructure of a ceramic produced by liquid phase sintering showing rounded grains, some residual porosity, and the intergranular glassy phase resulting from the liquid phase. (From R. W. Davidge, Mechanical Behavior of Ceramics, copyright 1979, p. 14. Reprinted with the permission of Cambridge University Press.)...

Fig. 4 Microstructure of a liquid phase sintered mullite ceramic with a relative density >99%. The ceramic had elongated grains with a grain size of > 5 pm and had a residual glassy phase surrounding the mullite grains...

In liquid-phase sintering, densification and microstructure development can be assessed on the basis of the liquid contact or wetting angle, (j), formed as a result of the interfacial energy balance at the solid-liquid-vapour intersection as defined by the Young equation ... 

Key words a-silicon carbide, liquid phase, sintering, mechanical properties, microstructure... 

V.A.lzhevskyi, L.A.Genova,A.H.ABressiani, J.C.Bressiani Liquid phase sintered SiC processing and Transformation controlled microstructure tailoring. Material research, 2000,3[4]131-138... 

MICROSTRUCTURE OF LIQUID PHASE SINTERED SILICON CARBIDE CERAMICS WITH HIGH FRACTURE TOUGHNESS ... 

Microstructure of Liquid Phase Sintered Silicon Carbide Ceramics... 

Figure 1 shows the features of polished surface and fracture section of two kinds of liquid-phase sintering of SiC ceramics. As can be seen, the microstructure of PLS sample (Fig. la) and HP sample (Fig. lb) is very uniform with small grains and the grains gq> was filled with liquid, forming the dense bodies. 

The ternary system W-C-Co is shown in Fig. 24 at 1423°C [102]. WC coexists with the Co phase and forms a pseudobinary lower melting eutectic between WC and Co. This eutectic facilitates full densification during liquid phase sintering. The carbon content must be kept close to the theoretical value because a decrease in total carbon content will lead to the formation of q carbides (W, Co>6C which are brittle and harmful to the performance of these materials. In modern hardmetals, also f.c.c. carbides such as TaC, NbC and TiC are admixed which increase the high-temperature performance. Figure 25 shows a microstructure of a modem WC/Co-based hardmetal containing about lOweight-% of f.c.c. carbides TiC, TaC, and NbC. 

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