Sustainable Nano-fluid-Assisted MQL Machining of Titanium Alloys: A Review of Trends, Barriers, and Future Pathways

This review presents an integrated assessment of the current state-of-the-art in sustainable machining, with particular emphasis on advanced lubrication and cooling strategies for titanium alloys. Given the high strength, low thermal conductivity, and chemical reactivity of titanium alloys, selecting environmentally responsible and effective machining approaches is essential. The review critically examines the growing use of nanoparticle-amended vegetable oils in Minimum Quantity Lubrication (MQL) systems, highlighting their tribological advantages, enhanced heat dissipation, improved wettability, and positive influence on tool wear, cutting forces, surface integrity, and overall machining efficiency. Complementary sustainable techniques including cryogenic cooling, hybrid cooling–lubrication methods, waste-reduction practices, and energy-efficient process optimization are also evaluated to position nano-enhanced MQL within the broader framework of green manufacturing. The discussion further incorporates sustainable manufacturing principles focused on reducing machining stages, minimizing material and energy consumption, and improving operational efficiency. By synthesizing current knowledge and identifying critical research gaps related to nanoparticle stability, high-speed lubrication delivery, mist formation, and environmental impact, this review contributes to directorial future studies toward more resource-efficient, eco-friendly, and high-performance machining solutions for titanium alloys.