Abstract 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.

中文翻译：

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硬质合金刀具单相铌加工磨损机理研究

摘要 在粒子加速器设施中，单相铌用于超导加速器组件。此类部件的加工诱导表面质量与加速器的功能密切相关。在这项研究中，研究了纵向车削中刀具磨损的发展及其对 Nb 工件表面质量的影响。未涂层硬质合金刀具在精加工条件下使用（切削速度 vc = 300 m/min 和进给 f = 0.05 mm/rev），磨损标准为 VBmax = 300 μm。借助高分辨率电子显微镜（SEM 和 TEM）对刀具的磨损机制进行了详细分析。此外，获得的结果与高压-高温条件（2 GPa 和 1000 °C）下的受控扩散偶实验相关。发现碳从 WC 扩散并形成 NbC 发生在铌 - 硬质合金界面上。磨损刀具的电子显微镜显示相同的扩散和化学相互作用机制导致快速后刀面磨损，但在前刀上形成的 NbC 完全抑制了刀具退化，从而起到刀具保护层的作用。