Fig. 1. Dimension of preprepared trapezoidal groove on Ti-6Al-4V substrate

Fig. 2. Underwater and in-air directed energy deposition and photos of as-repaired samples. (a) Schematic of underwater directed energy deposition (UDED); (b) actual manufacturing process of UDED; (c) as-repaired sample by UDED; (d) schematic of in-air directed energy deposition (in-air DED); (e) actual manufacturing process of in-air DED; (f) as-repaired sample by in-air DED

Fig. 3. Microstructures of repaired zone of Ti-6Al-4V repaired by UDED and in-air DED. (a)-(c) Microstructures repaired by UDED; (d)-(f) microstructures repaired by in-air DED

Fig. 4. Electron back scatter diffraction (EBSD) maps showing the microstructures. (a) Microstructure repaired by UDED; (b) microstructure repaired by in-air DED; (c) inverse pole figure of microstructure repaired by UDED; (d) inverse pole figure of microstructure repaired by in-air DED

Fig. 5. Transmission electron microscopy (TEM) analysis. (a) TEM image of the top region of UDED microstructure; (b) bright field image showing α′ lath martensite in the middle region of UDED microstructure; (c) selected area electron diffraction (SAED) pattern of UDED microstructure; (d) TEM image of the top region of in-air DED microstructure; (e) bright field image showing α lath in the middle region of in-air DED sample; (f) SAED pattern of in-air DED microstructure

Fig. 6. Microhardness analysis of three samples. (a) Microhardness distribution of repaired zone; (b) average microhardness

Fig. 7. Polarization curves of UDED specimen, in-air DED specimen and substrate in 3.5% NaCl solution. (a) Potentiodynamic polarization curves; (b) Tafel polarization curves

Fig. 8. Electrochemical impedance spectroscopy (EIS) of UDED Ti-6Al-4V, in-air DED Ti-6Al-4V, and substrate. (a) Nyquist plot; (b)(c) Bode plots; (d) equivalent simulated circuit used for EIS analysis

Fig. 9. SEM images and energy dispersive spectroscopy (EDS) analysis of the surfaces before and after corrosion tests. (a) Surface of UDED Ti-6Al-4V before corrosion test; (b)-(d) surface of UDED Ti-6Al-4V after corrosion test and EDS analysis of lumps in corrosion pits; (e) surface of in-air DED Ti-6Al-4V before corrosion test; (f)-(h) surface of in-air DED Ti-6Al-4V after corrosion test and EDS analysis of lumps in corrosion pits; (i) surface of the substrate after corrosion test