Effect of WC or NbC addition on lattice parameter of surrounding structure in Ti(C_0.7N_0.3)-Ni cermets investigated by TEM/CBED

The changes in the lattice parameters of the solid solutions in the Ti(C_0.7N_0.3)-WC-Ni and Ti(C_0.7N_0.3)-NbC-Ni systems were first shown quantitatively by the CBED (Convergent Beam Electron Diffraction) technique together with TEM (Transmission Electron Microscopy) microstructure characterization. The extent of the changes in the lattice parameters between core and rim differs in the case of WC and NbC additions. No change in the lattice parameters is observed in the Ti(C_0.7N_0.3)-WC-Ni cermets, in contrast to the Ti(C,N)-NbC-Ni cermets where significant changes in the lattice parameters are observed. The difference in the parameters is correlated with the core/rim structure, which disappears in the Ti(C,N)-NbC-Ni cermets when a large amount of NbC is added, and is discussed based on thermodynamic arguments. Large strain in the core and rim structure, especially near the core/rim interface, is also observed from the HOLZ (High Order Laue Zone) line splitting.