Evaluation of the wear of plasma-nitrided and TiN-coated HSS drills using conventional and Micro-PIXE techniques

The machining performance of high-speed steel (HSS) twist drills that were plasma-nitrided before applying physical vapor deposition (PVD) titanium nitride (TiN) coating was evaluated and compared with that of representative, commercially TiN-coated drills. The performance criteria were (i) the tool lives from the flank wear land measurements of the drills, and (ii) the wear features from micro particle-induced X-ray emission (Micro-PIXE), SEM and EDS examinations of two representative TiN-coated drills. The flank wear measurements indicated that the pre-nitrided drills had longer tool life than the commercial drills. The wear features of the pre-nitrided drill indicated that the TiN coating was subjected to progressive wear processes. On the other hand, the wear patterns of the commercial drill revealed that the TiN coating experienced interfacial spalling. Plasma nitriding prior to the application of the TiN coating is one explanation for the improvement in the machining performance of the pre-nitrided drills and for the observed differences in the wear mechanisms of the two types of drills.