Bai, Qiong (2014-12). Interactions Between Wear Mechanisms in a WC-Co / Ti-6Al-4V Machining Tribosystem. Master's Thesis.
The objective of this research work is to identify and analyze the interactions between wear mechanisms in a machining tribosystem, and to confirm the fundamental physicochemical material interaction behavior through tribometric tests. The machining tribosystem under study involves dry turning of a grade-5 titanium alloy (Ti-6Al-4V) with uncoated tungsten carbide-cobalt (WC-Co) cutting tools. The interactions being investigated involve both individual and combinations of macro and microstructural wear mechanisms that are predominantly force or temperature controlled. The worn surface obtained with different operational parameters was examined by scanning electron microscopy (SEM) and the elemental composition analyzed by energy dispersive spectroscopy (EDS). In addition, the topology of worn tools was characterized through scanning by a 3D optical surface profiler. The following major interactions were observed. At low cutting speeds, adhesion of Ti alloy and minor diffusion of C was observed (which increases with feed). At medium and high cutting speeds, the increased diffusion of Co led to WC grain pullout forming a crater, followed by the adhesion of Ti alloy. Also, at low feed rates C pullout and deposition was observed. Machining process conditions were appropriately represented in ball-on-disc tribometric bench tests to study the associated material behavior - two of the above interactions were confirmed. These led to recommendations to increase productivity by enabling selective wear mechanism interactions (though parameter selection) thus providing a better understanding of how the final worn tool surface is generated.