Wear of nanostructured tool coatings bonded to turning inserts dry turning a tantalum tungsten alloy

The machining of tantalum alloys using nanostructured coatings bonded to tungsten carbide turning inserts are investigated and presented in this thesis. Turning experiments were conducted on an alloy composed of 98 wt.% tantalum and 2 wt.% tungsten, and tool wear was quantified at moderate cutting speeds. A post-test only experimental design was used to compare the effect of PVD coated tools against an uncoated tool. Surface roughness experiments were compared to theoretical values at various depths of cut, cutting speed, and feed rate. Experimental data was compiled to quantify tool wear and compared to known wear mechanisms. High-speed video recordings of the machining operation were analyzed to determine the mechanisms of chip formation in addition to tool life and tool wear. Titanium-based coatings were found to extend the tool life when compared to an uncoated tool. Measured surface roughness was found to be higher than the calculated theoretical values. The wear mechanisms were classified as chipping and notch wear when machining this particular alloy. The existence of a built-up edge was prevalent during the machining experiments, and the machining chips collected during the analysis were compared to existing chip formation models. A high-speed video montage of the metal chips leads the author to designate a new mechanism of chip formation when machining this particular alloy and is known as the 'continual capricious chip formation mechanism', which is described in section 5.4. The thesis has shown that the machining of this tantalum alloy machines unlike any other metal alloy as discussed in the literature.