Surface nanocrystallization of Ti–45Al–7Nb–0.3W intermetallics induced by surface mechanical grinding treatment

• Surface mechanical grinding treatment was conducted on a Ti–45Al–7Nb–0.3W alloy.
• The γ→α2 phase transformation is observed.
• Nanocrystallized α2 grains (20 nm) are found in the treated surface.
• The micro-hardness of the top surface increases significantly, which is 50% higher than that of the substrate.
• The mechanisms of γ→α2 phase transformation and nanocrystallization are proposed.

Surface mechanical grinding treatment was conducted on a Ti–45Al–7Nb–0.3W intermetallics. The results show that the penetration depth plays an important role in the microstructural evolution. The γ→α2 phase transformation is observed at a penetration depth of 100 μm. Nanocrystallized α2 grains (20 nm) are found in the treated surface at a penetration depth of 200 μm. After the surface mechanical grinding treatment, the micro-hardness of the top surface increases significantly, which is 50% higher than that of the substrate. It is also found that the γ→α2 phase transformation is induced by the localized strain in the surface, while the mechanism for the nanocrystallization is proposed to be the twin–twin intersection.