Microstructural analysis of wear micromechanisms of WC–6Co cutting tools during high speed dry machining

• Microstructure damage of WC-6Co uncoated carbide tools during dry turning of AISI 1045 steel was studied.
• Disarrangement of the WC-6Co microstructure due to the severe tribological conditions on tool contact surfaces was observed.
• Dislocation formation and intergranular microcrack (at WC/WC or at WC/Co interfaces) micromechanisms were identified.
• Plastic deformation and intragranular microcraking of the WC grains were observed.
• Plastic deformation of the WC-6Co material and extrusion or removal of binder phase between the WC grains were observed.

This original study investigates the damages of WC–6Co uncoated carbide tools during dry turning of AISI 1045 steel at mean and high speeds. The different wear micromechanisms are explained on the basis of different microstructural observations and analyses made by different techniques: (i) optical microscopy (OM) at macro-scale, (ii) scanning electron microscopy (SEM), with back-scattered electron imaging (BSE) at micro-scale, (iii) energy dispersive spectroscopy (EDS), X ray mapping with wavelength dispersive spectroscopy (WDS) for the chemical analyses and (iv) temperature evolution during machining. We noted that at conventional cutting speed Vc ≤ 250 m/min, normal cutting tool wear types (adhesion, abrasion and built up edge) are clearly observed. However, for cutting speed Vc > 250 m/min a severe wear is observed because the behavior of the WC–6Co grade completely changes due to a severe thermomechanical loading. Through all SEM micrographs, it is observed that this severe wear consists of several steps as: excessive deformation of WC–6Co bulk material and binder phase (Co), deformation and intragranular microcracking of WC, WC grain fragmentation and production of WC fragments in the tool/chip contact. Thus, the WC fragments accumulated at the tool/chip interface cause abrasion phenomena and pullout WC from tool surface. WC fragments contribute also to the microcutting and microploughing of chips, which lead to form a transferred layer at the tool rake face. Finally, based on the observations of the different wear micromechanisms, a scenario of WC–6Co damages is proposed through to a phenomenological model.