Fig. 1 Microstructure and composition of the materials. a SEM image of the W alloy; b SEM image of WC powders

Fig. 2 Schematic diagram of the DED platform and process

Fig. 3 Micro morphologies in the WC-Ni-Co melting injection zone. a Initial microstructure of the WC coating; b-e EDS mapping of the W, C, Ni and Co elements

Fig. 4 Unmelted WC particles in the single DED track. a SEM image of the top view in the transverse section of the single track; b schematic diagram of the transverse section of the single track

Fig. 5 Transverse sections of the single tracks with different process parameters. (Some cross-sections of the tracks (10-15 mm/s) were quoted from our previous research [23]). a Forming quality of the single tracks with different process parameters; the track at a scanning speed of 5 mm/s and a power of b P = 1000 W, c P = 1250 W, d P = 1500 W, e P = 1750 W; the tracks at a scanning speed of 10 mm/s and a power of f P = 1500 W, g P = 1750 W [23]; the tracks at a power of 2500 W and a scanning speed of h 25 mm/s, i 30 mm/s

Fig. 6 SEM morphology and EDS maps of the pore in the base material below the fusion line. a SEM image of the pore; b-d elemental mapping distribution of W, Ni, and Co

Fig. 7 SEM image and EDS elemental distribution of the pore at the fusion line. a SEM image of the pore with an spherical shape; b-d elemental distribution of W, Ni, and Co

Fig. 8 Interfacial microstructures at the fusion line in different tracks. a Interfacial microstructure was W2C phase; b the interfacial microstructure was W + W2C phase; c the half-melted area in the tungsten alloy below the fusion line

Fig. 9 Numerical simulation results of the DED track. a Temperature field of the melting process; b a comparison of the melt pool size between the experimental and the simulation results; c the size of the vaporization area with a temperature range of 2730-2785 °C; d the half-melted area of the tungsten alloy

Fig. 10 Size of the vaporization area with a temperature range of 2785-2730 °C and solidification rate of the tracks with different DED process parameters. a Tracks at 2500 W with changed scanning speeds; b the tracks at 10 mm/s with changed laser powers

Fig. 11 Cross-section and microstructure of the track without powder feeding. a Macroscopic cross-section of the track (2500 W, 15 mm/s); b SEM image of the microstructure in the yellow box marked in Fig. 11a; c cross-section of the track (2500 W, 15 mm/s, the surface was preheated by a laser beam (1000 W, 10 mm/s)); d macroscopic cross-section of the track (2000 W, 10 mm/s); e macroscopic cross-section of the track (2000 W, 5 mm/s)

Fig. 12 Schematic diagram of vaporization of the binder phase and pore formation process. a Formation of a half-melted zone below the fusion line; b the evaporation of Ni/Co in the vaporization area; c the floating process of pores; d the merge of pores in the melt pool