Influence of binder metal and surface treatment on the corrosion resistance of (W,Ti)C-based hardmetals

The effect of a nitridation surface treatment on the microstructure and corrosion resistance of Co and Ni-binder (W,Ti)C-based hardmetals with additions of (Ta,Nb)C was investigated. Nitridation treatment produces a surface layer with a higher hard phase (Ti,Ta,Nb,W)(C,N) content. The near-surface layer thickness and microstructure are affected by the choice of binder (Co respectively Ni). The corrosion resistance of the hardmetals was characterized using linear sweep voltammetry. The microstructure of the hardmetals was determined before and after corrosive attack by optical microscopy and SEM. The results of the corrosion tests and microstructure analyses are interpreted in terms of the correlation between the hardmetal morphology and porosity and ion transport through the interface binder-electrolyte. The nitridation treatment of the hardmetals strongly increases the resistance to aggressive corrosion media for hardmetals both with Co and Ni-binder phase and thus may positively influence the hardmetal lifetime in cutting applications in chemically aggressive environments.