The microstructure of tungsten carbide and titanium carbide base cermets has been evaluated on the basis of wettability of the carbide phase. Incomplete wetting was found to result in a coalescence of the carbide phase leading to an apparent increase in the carbide particle size. Improvement in the wettability of the nickeltitanium carbide systems by the addition of molybdenum was found to promote the dispersion of the carbide phase and to lead to improved hardness and impact resistance.

315volume fraction of pores according to the Loeb equation. Depending on the extent of the pores, the conductivities of the other specimensfall into the region bonded by the dashed and solid lines in Fig. 1. These results demonstrate the importance of the shape and distribution of pores in their effect on conductivity. It is therefore important that the pore structure be ascertained before any of the relations between porosity and conductivity are employed. Unless the pore structures correspond to the model on which the relations are based, errors in the calculated conductivities may result. ( 5 ) Effect of Grain BoundariesThe thermal conductivity measurements on specimens of differing crystal sizes (Figs. 4 to 8) show that identical values were obtained when the effect of porosity and impurities was taken into account. These results support the conclusions reached in the theoretical analysis and indicate that for the range of grain sizes, materials, and temperatures considered, the effect of grain boundaries on thermal conductivity is negligible. Further confirmation has been obtained by the identical values between the aggregates and single crystals at temperatures below 300°C. Finally, the temperature dependence of the polycrystalline aggregates also indicates that in dense pure materials, no other resistance except the lattice resistivity is operative.(1956).

The modes of fracture and slip in cemented carbides were observed. Fracture and slip patterns in cemented carbides were found to vary with the microstructures which in turn were determined by the relative surface energies of various phases. The influence of particle size and metal binder content in cemented Tic and WC was also investigated. The fracture and slip in these systems are discussed in terms of the role of the metal film surrounding the carbide grains.

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