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

Abstract

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 N 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.

Experimental investigation of tool wear characteristics and analytical prediction of tool life using a modified tool wear rate model while machining 90 tungsten heavy alloys

“…Such disarrangement could be due to abrasion that would lead to micro-cracks at WC/WC or at WC/Co interfaces or chipping due to the alternative stress. 4,10 Consequently, few deep grooves or slip line traces on the surface of WC grains on the worn flank surface were observed. In addition, a prominent adhesion layer was also found.…”

“…6–8 Chen et al 9 evaluated abrasiveness index and observed diffusion, chemical, abrasive and micro-chipping as the major cause for rapid crater wear, while dry machining high chromium cast iron using polycrystalline cubic boron nitride (PCBN) inserts. Similarly, Kagnaya et al 10 observed severe wear near chip/tool contact due to abrasion and pullout phenomena during dry machining on AISI 1045 steel using tungsten carbide (WC)-6Co uncoated carbide tools and Zhang et al also evaluated tool failure for TC21 alloy under dry machining using coated carbide tools, and from scanning electron microscopic (SEM) analysis, it was found that adhesion and chipping were significant factors responsible for tool failure. Tang et al 11 found that the predominant wear mechanism changed as the hardness of the work material changed for PCBN tool during dry machining of AISI D2 hardened steel by varying the hardness in the range of 40–60 hardness Rockwell C (HRC) under similar cutting conditions.…”

Experimental Characterization of Tool Wear Morphology and Cutting Force Profile in Dry and Wet Turning of Titanium Metal Matrix Composites (Ti-MMCs)

“…Therefore, the tribological friction and wear can be attributed to areas of two new surfaces, in which the slip speed between the two new surfaces at the small edge of the cutting in these regions is close to zero [28,29]. Hence, it seems that the flatness and cleanliness of the contact surface can be attributed to static friction [30]. Adhesive chips on the tool surface may act as a barrier against abrasion wear.…”

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“…Kagnaya et al investigated the effects of cutting parameters on cutting tool wear, nding that cutting temperature increases with cutting speed and cutting tool wear increases with cutting temperature. Moreover, cutting forces decreases as cutting speed increases [23]. Das et al studied the effects of cutting parameters on cutting tool wear, and found that machining depth and cutting speed are the most important parameters that affect cutting tool wear and that cutting tool wear increases continuously with cutting speed and decreases as feed rate increases.…”