Machinability and tool wear mechanism in the high-speed milling of TiAl alloys with different microstructures

Titanium aluminides (TiAl) are potential candidates for replacing nickel-based superalloys in aircraft engines. This is due to TiAl alloys’ superiority in high-temperature strength, low density, and corrosion resistance. However, the room-temperature brittleness is one of the main problems of TiAl alloys, which will induce the difficulties of machining and poor surface quality of machined components, further hindering their wide application in the aerospace industry. This work focuses on the machinability and tool wear of TiAl alloys with different microstructures obtained at heat-treatment temperatures of 1150 °C, 1290 °C and 1370 °C. The machinability is evaluated by cutting forces, chip morphologies, machined surface quality, subsurface microstructure and tool wear by milling experiments at spindle speeds of 2000–6000 rpm. The cutting forces at 6000 rpm are decreased by ∼25–26 % compared to those at 2000 rpm. The surface quality is improved at a spindle speed of 4000 rpm (surface roughness is decreased by a maximum of ∼21 %). The tool flank wear (VBmax) at the spindle speed of 6000 rpm is increased by ∼37–42 % compared to those at 2000 rpm. Further, the lamellar chip formation mechanism of TiAl alloys is revealed. The lamellar plastic deformation of the machined subsurface is analyzed. The dominant tool wear mechanism is adhesive wear. The machinability of TiAl alloys is improved by high-speed cutting since thermal softening facilitates the brittle-ductile transition at cutting regions. Conversely, the limitation is that the extra heat generation under higher speed cutting will increase tool wear and degrade surface finish. The formation of lamellar chips also increases the machining difficulty. These findings provide an understanding of machinability and tool wear behavior in high-speed machining of TiAl alloys with different microstructures for aerospace applications.