Owing to its outstanding physical and mechanical properties, polycrystalline diamond (PCD) is ideal for cutting titanium alloys. However, the high temperature and stress caused by the interaction of tool surface and chip flow lead to different types of wear. This paper investigates the wear mechanisms of PCD tools in three different tribological regions: sticking zone, transition zone, and sliding zone, when machining titanium alloy Ti6Al4V. The tribological behavior of PCD tools in the wear processes were analyzed through both experiments and theoretical calculations. Analytical models of stresses and temperature distribution were developed and validated by turning experiments. PCD tools, consisting of diamond grains of different sizes: CTB002 (2 μm), CTB010 (10 μm), and CTM302 (2–30 μm), were used to cut Ti6Al4V at the normal cutting speed of 160 m/min and high cutting speed 240 m/min. It was found that adhesion, abrasion and diffusion dominated the wear process of PCD tools in different worn regions. Microscopic characters showed that the wear mechanisms were different in the three tribological regions, which was affected by the distribution of stresses and temperature. “Sticking” of workpiece material was obvious on the cutting edge, abrasion was severe in the transition zone, and adhesion was significant in the sliding zone. The shapes and morphological characters in different worn regions were affected by the stresses distribution and the types of PCD materials.

The significant amount of heat and friction generated in machining Ti-6Al-4V affect the cutting performance and result in serious problems such as severe tool wear and poor surface quality. Graphene oxide (GO) nanoparticles have excellent thermal conductivity and high lubrication capability and have emerged as a promising solution to the heat and tribology issues. As an additive material, GO nanoparticles mixed in base fluids may lead to significant increase in thermal conductivity and lubrication capability, which in turn, could result in smaller cutting forces and lower cutting temperature in the cutting zone. This paper presents new models of using GO nanofluids in turning processes which can accurately predict the change in cutting temperature and cutting forces. The cutting temperature model was created by considering the thermal conductivity and specific heat of the GO nanofluids along with their heat transfer coefficient and friction coefficient, whereas the cutting force model was developed by taking into account friction, tool geometry and the friction coefficient associated with the thermal properties of nanofluids.