Surface Integrity of VAR-Cast Ti-48Al-2Cr-2Nb Alloy After W-EDM, Dry Milling and Subsequent Annealing Treatments

The surface integrity of γ-TiAl alloys is critical for the performance and reliability of aerospace components due to their limited ductility and inherent brittleness. Although wire electrical discharge machining (W-EDM), milling and heat treatments are commonly employed during the manufacture of γ-TiAl parts, their combined influence on surface integrity remains insufficiently understood. This study investigates the effects of finishing operations and post-machining heat treatments on a Ti-48Al-2Cr-2Nb alloy produced by vacuum arc remelting (VAR). Specimens were sectioned by W-EDM and subsequently finished by dry milling. Surface integrity was evaluated through metallographic observations, microhardness measurements, and residual stress analysis, while annealing treatments between 700 and 1100 °C for 2 h were applied to assess the recovery of machining-induced alterations. W-EDM generated a cracked surface layer, revealing a significant limitation of this process for γ-TiAl components. Milling removed the damaged layer and produced a defect-free surface, however, it induced a plastically deformed subsurface region about 50 μm thick, accompanied by increased hardness and residual stresses. Annealing at 700 °C provided only partial recovery, whereas treatments at 900 °C and above promoted complete recrystallization of the affected layer, restoring hardness to values close to those of the bulk material. The results demonstrate that milling followed by annealing at 900 °C for 2 h effectively restores surface integrity without altering the bulk microstructure.