Fig. 1. Schematic of WLMD forming device and forming principle. (a) Forming device^[16]; (b) illustration of the paraxial WLMD principle^[20]; (c) illustration of the coaxial WLMD principle^[21]

Fig. 2. Three wire directions of the paraxial WLMD^[25]. (a) Pushed configuration; (b) perpendicular configuration; (c) pull configuration. Contact point position between wire and molten pool^[28]. (d) Front-wire-feeding mode; (e) center-wire-feeding mode; (f) rear-wire-feeding mode

Fig. 3. Three typical technical principles of coaxial wire feeding^[33]. (a) Coaxial wire feeding inside three-beamlaser; (b) coaxial wire feeding insidemulti-beam laser; (c) coaxial wire feeding through annular laser beam

Fig. 4. Schematic of process modeling for power density in coaxial wire feeding laser additive manufacturing^[39]

Fig. 5. Titanium alloy formed by equipment for WLMD with coaxial wire feeding^[40]. (a) Coaxial wire feeding deposition machine; (b) laser beam shape analysis in different planes; (c) formed cuboid out of Ti-6Al-4V; (d) cross and longitudinal section of the formed cuboid

Fig. 6. Formation diagram of titanium alloy microstructure^{[46, 53]}. (a) Change of phase content of α + β titanium alloy with temperature; (b) phase transformation at different cooling rates; (c) flaky α phase at the top layer; (d) net-basket microstructure in the middle

Fig. 7. Titanium alloy prepared by underwater WLMD^[57]. (a) Schematic of underwater WLMD experimental system; (b) cuboid and its microstructures prepared by underwater WLMD

Fig. 8. Simulation of WLMD titanium alloy^[63]. (a) Model meshing and residual stress distributions; (b) residual stress distributions along different paths

Fig. 9. Effects of ultrasonic micro-forging treatment on the microstructure and properties of WLMD titanium alloy^[64]. (a) Grain morphology of samples under different amplitudes and forging forces; (b) microhardness of samples under different amplitudes and forging forces