A Methodology to Systematically Investigate the Diffusion Degradation of Cemented Carbide during Machining of a Titanium Alloy

Using Ti6Al4V as a work material, a methodology to systematically investigate the diffusion degradation of cemented carbide during machining is proposed. The methodology includes surface characterization of as-tested worn inserts, wet etched worn inserts, metallographic cross-sectioned worn inserts as well as the back-side of the produced chips. Characterization techniques used include scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Auger electron spectroscopy (AES) and time of flight secondary ion mass spectroscopy (ToF-SIMS). The results show that the characterization of wet etched worn inserts gives quick and useful information regarding the diffusion degradation of cemented carbide, in the present work the formation of a fine crystalline W layer (carbon depleted WC layer) at the tool-work material interface. The present study also illuminates the potential of AES analysis when it comes to analyzing the degradation of cemented carbide in contact with the work material during machining. The high surface sensitivity in combination with high lateral resolution makes it possible to analyze the worn cemented carbide surface on a sub-µm level. Especially AES sputter depth profiling, resulting in detailed information of variations in chemical composition across interfaces, is a powerful tool when it comes to understanding diffusion wear. Finally, the present work illustrates the importance of analyzing not only the worn tool but also the produced chips. An accurate characterization of the back-side of the chips will give important information regarding the wear mechanisms taking place at the tool rake face–chip interface. Surface analysis techniques such as AES and ToF-SIMS are well suited for this type of surface characterization.