Contact fatigue behaviour of CVD coated cemented carbides in dry and wet conditions

Cycling contact fatigue indentation tests in dry and wet conditions were conducted in cemented carbides CVD-coated with Ti(C,N)/a-Al2O3 and Zr(C,N)/a-Al2O3 systems. In dry contact experiments, all imprints presented a deformed area where the coating was still present after the test. Formation of cracks was visible at the edge of the contact point of the imprint. On the other hand, under wet conditions, almost all imprints presented a ring where the a-Al2O3 had been removed, driven by a corrosion-fatigue process. Exceptionally, for Cr-containing cemented carbides combined with Zr(C,N)/a-Al2O3 coating, no delamination of a-Al2O3 was observed after the test under wet conditions. This result suggests that the combination of fine-grained cemented carbides and coating systems with low coefficient of thermal expansion may be of advantage to resist degradation by cyclic contact fatigue. Furthermore, the response to fatigue by contact loads can be enhanced by tailoring/combining cemented carbides and CVD coating systems which present higher chemical stability, and both higher intrinsic plasticity and resistance to plastic deformation.