Characterisation and wear response of metal-boride coated WC–Co

Wear resistant transition metal boride coatings have received comparatively little investigation. In the present work, a series of CrB2, Mo2B5 and WB coatings were successfully applied to WC–6wt.%Co cutting tool inserts using unbalanced magnetron sputtering technology. The CrB2 coatings were fully crystalline and had a {1 0 1} preferred orientation, while the Mo2B5 coatings although containing some crystallinity were mainly amorphous. The WB coatings on the other hand were produced in the crystalline and the amorphous states (designated WB(XL) and WB(AMOR) respectively). A range of hardness and scratch resistance was observed, the hardest coating being CrB2 (HV ∼2764 at room temperature), while the toughest was the WB(AMOR) coated WC–Co, the latter showing high resistance to both adhesive and cohesive failure. Machining tests carried out on commercial purity titanium (CP-Ti) revealed that the WB(XL) coated WC–Co inserts were the most resistant to rake face wear. Such wear, attributed to a combination of discrete plastic deformation and dissolution-diffusion mechanisms, was minimised by the ability of the WB(XL) coatings to display a combination of good high temperature hardness (strength) and chemical inertness with respect to CP-Ti.