Study of wear mechanisms of cemented carbide tools during machining of single-phase niobium

In particle accelerator facilities, single-phase niobium is used in superconducting accelerator components. Machining induced surface quality of such components is strongly connected to the functionality of accelerators. In this study, tool wear development and its influence on the surface quality of Nb workpiece have been investigated in longitudinal turning. Uncoated cemented carbide cutting tools were used under finishing conditions (cutting speed vc = 300 m/min and feed f = 0.05 mm/rev) up to the wear criterion of VBmax = 300 μm. A detailed analysis of wear mechanisms of the cutting tool was conducted with help of high resolution electron microscopy (SEM and TEM). Further, the results obtained were correlated with controlled diffusion couples experiments under high pressure – high temperature conditions (2 GPa and 1000 °C). Diffusion of carbon from WC and formation of NbC was found to occur on the niobium – cemented carbide interface. Electron microscopy of the worn tools reports identical mechanisms of diffusion and chemical interaction which lead to rapid flank wear, yet formation of NbC on the rake completely inhibits tool degradation and thus acts as tool protection layer.