Chemical Effects on Formation and Propagation of Comb Cracks in Coated Cemented Carbide Milling Inserts

Abstract: The report aims to investigate the influence of chemical reactions on comb crack formation and propagation in coated cemented carbide milling inserts with different compositions. A series of novel experimental techniques have been developed and applied to understand oxidation and corrosion effects on comb cracks. Furthermore microstructure changes in the region of the comb cracks on worn milling inserts were studied by high resolution microscopy. It has been observed that the main effect of the oxidation and corrosion on comb cracks is connected to an attack of the binder phase, affecting its composition, distribution and morphology. Different comb crack types for dry and wet milling have been observed. In the presence of cooling media (wet machining) inserts present lateral cracks (fatigue induced) connected to the principal comb crack, which form at regions where the binder has been strongly corroded. Despite the addition of Cr and (Ta,Nb)C enhance both the oxidation and corrosion attack resistance have a minor effect on the formation and propagation of comb cracks. Schematic models based on the experimental results and scientific discussions are presented to understand the influence of oxidation and corrosion in the formation and propagation of comb cracks.