Effect of mechanical surface treatments on Ti–6Al–4V direct metal deposition parts

The effect of surface treatments, including aggressive milling, rotational burnishing, and nonrotational burnishing, on Ti–6Al–4V DMD (direct metal deposition) parts was investigated. Particular emphasis is on the question of whether these surface treatments could induce the plastically deformed and work-hardened layer that was proven to enhance the fatigue resistance of titanium alloys and was a key step for recrystallization. Through the microhardness examination and microstructure analysis, it was found that the rotational burnishing process was able to work harden the material deeper than 1000 μm, while the work-hardened layer generated by the nonrotational process was ∼600 μm and that for aggressive milling was less than 10 μm. Because surface finish is another critical factor for the resistance of fatigue crack initiation, it was also evaluated for these treatments.