C/N ratios in TiCN-TiC-WC-Cr3C2-Ni cermets can be intentionally modified by changing the composition of the presintering atmosphere. This affects not only the sinterability but also the final microstructure of these materials. Melting occurs at lower temperatures as the nitrogen content of the presintering atmosphere rises. However, the final densities are lower due to the precipitation of free carbon. Grain growth of the carbonitride phase is accelerated in samples presintered in N2 due to the activation of solution reprecipitation kinetics. Finally, the precipitation of the Cr-rich M7C3 carbide can also be controlled by the appropriate selection of the presintering atmosphere up to 7.8 wt.% Cr contents.

Microbeam testing is proposed as a new method for analysing the mechanical properties of individual microstructural features in WC-Co hardmetals; i.e. portions of WC grains or a single metallic ligament. Firstly, cantilever microbeams with dimensions below the microstructural scale of the material are machined by means of a focused ion beam (FIB). Afterwards, these beams are bended to fracture by means of an instrumented nanoindenter. In this way, both portions of WC grains and binder phase ligaments are broken while simultaneously recording the load and the vertical displacement of the nanoindenter tip. These cracking events are detected as sudden steps in the load vs. displacement curves. Afterwards, a scanning electron microscope is used to measure the distance from the main crack to the beam clamping. From these data, the stresses at which portions of cobalt ligaments and WC grains fail are estimated from linear elastic theory and FEM models.

In TiCN-W-Cr-Ni cermets produced by liquid phase sintering melting occurs at lower temperatures as their Cr content increases. For low Cr additions (up to 4 wt.%) eutectic temperatures are close to those found in the TiC-WC-Ni system. For 8 wt.% Cr and above, temperatures are similar to those found in the Cr-Ni-C system. The precipitation of M7C3 carbides is observed to start at 8 wt.% Cr in samples sintered at 1425 degrees C for 1 h. This sets a limit for the Cr solubility in the binder phase of these cermets around 18 wt.%. The dissolution of WC and Cr3C2 particles starts at temperatures as low as 1150 degrees C, but that the homogenization of the binder phase is only achieved after melting. The carbonitride phase exhibits the typical precipitation of inner and outer rims onto Ti(C,N) cores. However, a fine precipitation of Ni-rich particles is found inside Ti(C,N) cores, likely related to coalescence phenomena.