Performance of MoS2-alloyed-TiAlSiN-Coated Cutting Tools in Dry Turning of Ti-6Al-4V Alloy

Machining titanium alloys is challenged by high friction and temperature at the tool–workpiece interface, leading to rapid tool wear and poor surface integrity. While cutting fluids during machining have been used to avert this, they have been observed to induce irreversible chemical reactions with the machined surfaces, while also presenting manufacturers with additional cutting fluid purchase, use, and disposal costs, in addition to environmental and health concerns. This has motivated a shift towards dry machining. This study investigates the performance of MoS2-alloyed TiAlSiN thin film coatings (referred to as n:MoS2) deposited by magnetron sputtering on tungsten carbide cutting tools for dry rough turning of Ti-6Al-4V alloy. After deposition, the MoS2-alloyed coatings maintained mechanical properties comparable to the TiAlSiN thin films (H ~ 10 GPa and H/E ~ 0.06), while significantly improving the tribological behaviour of the coated tools (coefficient of friction: TiAlSiN ~ 0.16 and n:MoS2 ~ 0.13). Moreover, the n: MoS2-coated tools exhibited reduced and steady cutting temperatures, smoother chip flow, and the lowest flank wear, VBB (~0.191 mm), corresponding to wear reductions of approximately 71% compared to the as-manufactured (VBB = 0.651 mm) and 20% relative to TiAlSiN-only coated tools (VBB = 0.239 mm). The enhanced performance was attributed to the effective self-lubrication and improved heat dissipation at the cutting interface. These results demonstrate the strong potential of MoS2-alloyed TiAlSiN coatings for enabling high-performance, environmentally sustainable dry machining of titanium alloys.