Study of Porosity in Uncoated Cemented Carbide Tools During Titanium Alloy Machining.

Abstract: During high speed machining of titanium alloys both the tool and workpiece material diffuse into one another affecting the surface integrity of the cutting tool edge and leading to fracture. One proposed mechanism by which the tool integrity is compromised results from the possible formation of porosity in to subsurface of the tool substrate close to the tool cutting edge. In this study the porosity in uncoated cemented carbide tools during titanium alloy machining is investigated. In order to simulate the diffusion process, diffusion couples between titanium and WC-6%Co are studied at various pressure (0 - 2.5 GPa) and temperature (800-1200 °C) conditions. Cross sectioned diffusion couples were analysed with SEM and XEDS. Pore formation was identified in two of the 6 samples that were analysed. The cause is unknown but believed to be Kirkendall porosity, where vacancies nucleate due to a net flux of vacancies towards the insert. As part of this study worn milling and turning inserts were also investigated. No voids were observed during analysis of the cross sectioned turning insert. In one milling insert groups of cavities are found in the binder phase, however, these are believed to not be formed by diffusion wear, but rather by plastic deformation. The presence of voids along the cutting edge is observed in one insert, the origin of these cavities are unknown. It’s the first time that porosity in titanium machining has been the focus of a study and it progresses the field forward.