Machinability and tribology investigation of nano-hybrid cryogenic-mql cooling system in milling titanium alloys for biomedical implant / Nurul Dayana Binti Mohd Noor

Centre for Mathematical Sciences

Thesis (Master) -- Universiti Malaysia Pahang Al Sultan Abdullah– 2025

Includes bibliographical references

Recent advancements have led to a significant increase in the demand for titanium alloys, particularly within the biomedical sectors. However, their poor machinability attributed to low thermal conductivity, high chemical reactivity, and a high strength-toweight ratio results in rapid tool wear, elevated cutting temperatures, and poor surface finish. Conventional cooling and lubrication methods often fail to effectively mitigate these challenges. This study investigates an advanced nano-hybrid cryogenic Minimum Quantity Lubrication (MQL) system for the end milling of Ti-6Al-4V using a PVDcoated carbide tool. A full factorial experimental design was employed to assess the influence of machining parameters, including cutting speeds (130 and 150 m/min) and feed rates (0.2 and 0.5 mm/rev), on tool wear and surface integrity. Two nanofluids SiO₂ and Al₂O₃, each containing 20 nm particles at a 1% concentration were evaluated. The SiO₂-based system significantly improved machinability by reducing adhesive and abrasive tool wear, extending tool life by 90%, and achieving a surface roughness of 0.2 μm, which is suitable for biomedical applications. This superior performance is attributed to SiO₂'s effectiveness in minimizing surface roughness and crack formation. In contrast, the Al₂O₃ nanofluid resulted in comparatively higher abrasive wear. The dominant wear mechanism observed was built-up edge formation leading to flank wear. Tribological analysis indicated negligible differences in the coefficient of friction between both nanofluids, confirming comparable lubrication efficiency. Optimal machining performance was achieved at a cutting speed of 130 m/min and a feed rate of 0.2 mm/rev. In conclusion, the proposed nano-hybrid cryogenic MQL system effectively addresses the limitations of conventional cooling methods, offering a sustainable and highperformance solution for improving tool life, wear resistance, and surface integrity in titanium alloy machining thereby supporting sustainable practices aligned with biomedical standards