On tool wear in drilling of wrought and additively manufactured Ti6Al4V alloy under nanofluid-assisted minimum quantity lubrication

Additive manufacturing (AM) technologies have enabled the production of complex titanium alloy (Ti6Al4V) components for aerospace and biomedical applications. However, these components often require subsequent machining as a post-processing step, where the high temperatures involved and the alloy's poor thermal conductivity may accelerate tool wear and compromise surface finish. Minimum quantity lubrication (MQL) with vegetable-based oils offers a sustainable alternative to conventional flood cooling, though its performance is limited by low heat dissipation and reduced pressure resistance. To enhance lubrication efficiency, nanoparticles may be dispersed in the base oil. In this study, a nanofluid composed of 0.1 wt% Al2O3 nanoparticles and 0.32 wt% SLS surfactant in soybean oil was tested along with pure soybean oil during drilling of two Ti6Al4V as-received states: wrought and electron beam melted (EBM). The cutting fluids were characterized for thermal conductivity, viscosity, wettability, and tribological behaviour. Fifty holes were drilled per condition, showing tool adhesion and abrasion as the main wear mechanisms, but with adhesion less severe when cutting the EBM alloy. In addition, the nanofluid reduced the worn area of the cutting edges by 42 % in the wrought alloy and by 75 % in the EBM alloy, effectively mitigating abrasive wear and chipping. Hole surface roughness values remained consistently low (Ra < 0.9 µm) across all conditions. Overall, the nanoparticles promoted a rolling effect at the tool-workpiece interface, with a superior response on the EBM alloy, ascribed to its higher hardness and acicular microstructure, possibly inducing more stable nanoparticle interactions and improved lubrication performance.