Fig. 1 Number of publications on SLM and EBM as keywords (Scopus, 30 December 2020)

Fig. 2 A schematic of a LPBF system [41]

Fig. 3 A schematic of electron beam melting (EBM)

Fig. 4 Schematic of a powder-fed, b wire-fed DED process [89]

Fig. 5 Central schematic represents an overview of the AM: a unreinforced Al7075 powder, b reinforced Al7075 powder, c Al7075 tend to solidify by columnar growth of dendrites, d suitable nanoparticles can induce heterogeneous nucleation and facilitate equiaxed grain growth, e many alloys exhibit intolerable microstructure with large grains and periodic cracks when AM using conventional approaches, as illustrated by the inverse pole figure, f functionalizing the powder feedstock with nanoparticles produces fine equiaxed grain growth and eliminates hot cracking [102]

Fig. 6 EBSD images of block specimen at different energy densities: a 44 J/mm3, b 66 J/mm3, c 111 J/mm3, d 222 J/mm3, e 333 J/mm3, and f 375 J/mm3 [112]

Fig. 7 a-c SEM images, d EBSD orientation map, e grain size distribution of the LPBF Al composites [103]

Fig. 8 a Scanning TEM (STEM) high-angle annular dark-field (HAADF) image showing the diamond(111)/Al interfacial area where Al4C3 interfacial layer and plate-like particles are developed, b the EDX spectrum of a typical interfacial particle is shown, c-f are elemental EDX maps for Al, O, Si, and C, respectively [118]

Fig. 9 Tensile properties of the pure AlSi10Mg, AlSi10Mg-Gr composites at different laser powers; a YS, b UTS, and c Elongation [119]

Fig. 10 The hardness of the pure AlSi10Mg, AlSi10Mg-Gr composites at different laser powers [119]

Fig. 11 Schematic representation of the formation of the TiB phase through an in situ reaction between Ti and TiB2: a starting powder mixture showing the fine distribution of TiB2 particles surrounding the larger Ti powders before sintering, b in situ formed needle-shaped TiB as well as semi-formed TiB, and unreacted TiB2 particles during sintering [137]

Fig. 12 a Particle shape and morphology of the starting TiB2 powder, b TEM images showing the microstructures of the SLM-processed Ti-TiB composite showing needle-shaped TiB particles embedded in a matrix of α-Ti grains with lamellar structure [146]

Fig. 13 a SEM and b bright-field TEM images of Ti-TiB composite materials after LPBF processing [149]

Fig. 14 High-magnitude morphologies of microstructures located on the top surface of LPBF-processed B4C/Ti composite parts at different laser power: a 125 W, 800 mm/s; b 150 W, 800 mm/s [158]

Fig. 15 Vickers microhardness and typical compressive true stress-strain curves of Ti-64, 0.5 wt% B4C (TMC1) and 1.0 wt% B4C (TMC2) [145]

Fig. 16 Mechanical properties of Ti-6Al-4V composite in the presence of the various amount of B4C: a Vickers hardness, b Young's modulus [33]

Fig. 17 Room temperature tensile stress-strain curves of a Ti-6Al-4V alloy; b Ti-6Al-4V-1.5wt% B4C [33]

Fig. 18 Tensile stress-strain curves of a Ti-6Al-4V; b Ti-6Al-4V-1.5 wt%B4C, at 500 °C [33]

Fig. 19 SEM analysis of fracture surface of a Ti-6Al-4V; b Ti-6Al-4V-1.5wt% B4C, at 500 °C [33]

Fig. 20 Comparison of open-cellular, mesh design models (unit cells) and corresponding EBM-fabricated mesh structures in decreasing order of density. a Octet truss, b G structure 3 (G3), c Rhombic dodecahedron, d Dode medium [142]

Fig. 21 TEM images of the printed composite: a bright-field (BF) micrograph, b morphology and distribution of reinforcements, c morphology of reinforcements replicated from the matrix and the SAED pattern of a TiC nanoparticle, d morphology and distribution of TiC nanoplatelets and the corresponding SAED pattern [143]

Fig. 22 a Tensile stress-strain curves of as-printed Ti-6Al-4V alloy and composite, b SEM fractography of the tensile fractured composite, c schematic illustration of the strengthening [143]

Fig. 23 Compressive stress-strain curves of 316L composites containing 5 vol% (solid) and 10 vol% (dashed) TiB2 nanoparticles [160]

Fig. 24 Change in a microhardness, b potentiodynamic polarization curves of 316L stainless steel SiC composites with the amount of SiC. The polarization test is carried out in 3.5 wt% NaCl solution while being exposed to air, and samples A, B, C, and D contain 4, 8, 12, and 16 wt% SiC, respectively [159]

Fig. 25 a SEM image of the stainless steel composite reinforced with 12 wt% V, b EDS line of the VC precipitate, c microhardness of the samples, d the wear behaviour of the samples. Specimens 1, 2, and 3, respectively, contain 9, 12, and 15 wt% V [161]

Fig. 26 a Optical microscope photographs of monolithic and composite sections, at 2.5 $\times$ magnification, b Vickers hardness of the monolithic and composite samples [164]