Diffusion-controlled growth of fcc-free surface layers on cemented carbides: Experimental measurements coupled with computer simulation

• The reliable atomic mobilities in liquid Co-Ti-Ta-W was established by the modified Sutherland equation.
• Fcc-free surface layer were produced on WC-Ti(C,N)-TaC-Co cemented carbides by one-step and two-step sintering in vacuum.
• The calculated volume fractions and elemental concentration profiles are in good agreement with the experimental data.

The recently developed Arrhenius formula of modified Sutherland equation was employed to calculate the self- and impurity diffusivities in liquid Co, Ta, Ti and W. The reliability of the calculated results was validated by comparing the experimentally measured and theoretically predicted data available in the literature with the presently predicted diffusivities. The obtained atomic mobility parameters were incorporated into Diffusivity Database for Cemented Carbides (CSUDDCC1) developed in our research group. In addition, fcc-free surface layer was produced on WC–Ti(C,N)–TaC–Co cemented carbides by gradient sintering in vacuum. SEM (scanning electron microscopy) coupled with EPMA (electron probe micro analysis) was employed to characterize the microstructure. Moreover, the concentration profiles and distributions of the elements on the gradient WC–Ti(C,N)–TaC–Co cemented carbides were also measured by EPMA. Based on the reliable thermodynamic database (CSUTDCC1) and diffusion database (CSUDDCC1), the volume fractions of different phases and elemental concentration profiles in the WC–Ti(C,N)–TaC–Co cemented carbides were simulated by means of DICTRA (DIffusion-Controlled TRAnsformations) software considering only the diffusion in the liquid binder phase. The simulation results taking the heating and cooling rates into account are in good agreement with the experimental data.