Effect of Ce Addition on the Machinability of Ti-6Al-4V Alloy

Ti alloys are difficult to machine, accounting for 50-75% of the final component price, necessitating urgent improvements in machinability to increase their demand in several fields. This study found that adding small amounts of Ce (0.1-2.0wt.%) significantly improves the machinability of Ti-6Al-4V alloy. Here, we systematically analyzed microstructural changes due to Ce addition and their effects on machinability and tensile properties. We found that adding 0.3wt.% Ce results in fine (80-100nm) Ce-oxides dispersion throughout the matrix, which effectively reduces chip length (192mm -> 12.5mm) and increases tensile strength from 840MPa to 956MPa without a significant decrease in ductility; however, the reduction in cutting torque was minimal (2.5Nm -> 2.3Nm). On the other hand, when 1.4wt.% Ce was added, Ce-oxide particles were not only finely distributed within the matrix but also coarsely (3 mu m-5 mu m) located along the prior beta grain boundaries, resulting in significant reductions in both chip length (192mm -> 4.5mm) and cutting torque (2.5Nm -> 1.9Nm). In this case, the tensile strength increased from 840MPa to 909MPa, but ductility slightly decreased due to cleavage fracture. Therefore, the addition of 1.4wt.% Ce is suitable when reducing cutting torque is more important than ductility, while 0.3wt.% Ce is preferable when reducing chip length and maintaining ductility are critical. This study is expected to contribute to expanding the industrial application of Ti components by reducing the machining costs of Ti alloys.