Fig. 1. Morphology of TC4 alloy powder

Fig. 2. Specimen preparation process. (a) Schematic diagram of device; (b) 3D model and scanning path; (c) physical objects during printing process; (d) schematic diagram of sampling in corrosion resistance performance test; (e) schematic diagram of sampling in friction and wear test

Fig. 3. Surface morphologies of formed specimens under different nitrogen volume fractions. (a) Pure argon gas; (b) 25%; (c) 50%; (d) 75%; (e) 100%

Fig. 4. Microstructures of formed specimens under different nitrogen volume fractions. (a) 0%; (b) 25%; (c) 50%; (d) 75%; (e) 100%

Fig. 5. Microstructures of formed sample in pure nitrogen atmosphere. (a) Top part; (b) central part; (c) interlayer junction

Fig. 6. Nitrided microstructures of formed specimen under nitrogen-containing atmosphere. (a) Microstructure morphology at low nitrogen content location; (b) microstructure morphology at high nitrogen content location

Fig. 7. XRD spectra of formed specimens under different nitrogen volume fractions

Fig. 8. Surface microhardness values of formed specimens under different nitrogen volume fractions

Fig. 9. Friction coefficients and wear losses of formed specimens under different nitrogen volume fractions. (a) Friction coefficient; (b) average friction coefficient and wear loss

Fig. 10. Wear track morphologies and three-dimensional contour diagrams of formed specimens under different nitrogen volume fractions. (a)(a1)(a2) 0%; (b)(b1)(b2) 25%; (c)(c1)(c2) 50%; (d)(d1)(d2) 75%; (e)(e1)(e2) 100%

Fig. 11. Polarization curves of formed specimens in SBF under different nitrogen volume fractions

Fig. 12. Metallographic diagrams of low-power formed specimens. (a) Overall metallographic diagram; (b) enlarged view of area A

Fig. 13. Cross-sectional morphology and nitride distribution. (a) Cross-sectional morphology; (b) nitride distribution

Fig. 14. Diagram of nitrogen action mechanism. (a) Mechanism of nitrogen action on surface of molten pool; (b) enlarged view of area A