Laser powder bed fusion (LPBF), as a typical additive manufacturing process, has the unique capability to consolidate powder in a layer-by-layer fashion according to user-defined configurations, using a laser as the energy source. Some typical metals, such as aluminum alloys, Ti alloys, Ni alloys, and stainless steel, have been successfully manufactured via LPBF and widely used in the aerospace, automobile, and marine industries. Inconel 718, an austenitic Ni-Cr-based superalloy, has an improved balance of creep, tensile properties, and corrosion resistance at 700 °C. To further improve the high-temperature performance of Inconel 718, incorporating hard and temperature-resistant ceramic particles within the Inconel matrix to produce metal matrix composites is regarded as a promising method. TiC particles are the most common ceramic reinforcements owing to their high melting point, high hardness, low density, and excellent friction and wear properties. In this study, LPBF was applied to prepare TiC-particle-reinforced Inconel 718 matrix composites with different TiC contents, and the effect of TiC content on the forming quality, microstructure, and mechanical properties of Inconel 718 composites was investigated.

The powders used were gas-atomized spherical Inconel 718 powder with a particle size distribution of 15-53 μm and irregularly shaped TiC powder with an average size of 1 μm. Powders with 0.5% (mass fraction) TiC and 1% TiC were prepared using a roller mixer. The TiC/Inconel 718 composite specimens were then fabricated with a BLT-S200 selective laser melting system using the optimized process parameters in an argon atmosphere. In addition, homogenization and solution aging heat treatment were performed on some of the tensile specimens. Subsequently, a roughness tester was used to evaluate the surface quality of the specimens. The porosity and defect distribution of the specimens were examined using optical microscopy (OM) and industrial computed tomography. The microstructures of the composites were observed using OM and scanning electron microscopy (SEM). Archimedes' method was used to measure the relative densities of the specimens. Vickers hardness was measured, and the tensile properties were examined using an electronic universal testing machine at room temperature. Moreover, the fracture morphology of the composite was characterized by SEM.

Compared with the as-deposited Inconel 718 superalloy, the addition of 0.5% and 1% TiC particles has little effect on the surface roughness of the sample. By adding 0.5% and 1% TiC particles, the increase in roughness of different surfaces of the composite block can be controlled within 5% (Fig. 3). The surface-forming quality of the Inconel 718 superalloy and its composites is good. The polished section of the Inconel 718 sample did not exhibit any apparent pores. However, several near-circular pores are observed in the polished section of the TiC/Inconel 718 samples (Fig. 4). The diameters of the pores in the Inconel 718 superalloy and its composites are concentrated between 20 and 70 μm, and most of the pores in the samples are <50 μm. The number of pores in the composites significantly increases with TiC content (Fig. 5). The relative densities of 0.5% TiC/Inconel 718 and 1% TiC/Inconel 718 are 99.55% and 99.32%, respectively (Table 2). The OM images of the section along the deposition direction of all samples exhibit the interlaced “fish scale” structure as normally observed in LPBF-fabricated metal parts (Fig. 6). The high-resolution SEM image reveals typical epitaxial crystallization in the microstructure of the Inconel 718 superalloy and its composites (Fig. 7). In addition, the reinforcing particles are homogeneously dispersed within the matrix, and their irregular edges and corners almost disappear (Fig. 8). The hardness of the composites increases with the TiC content. When the TiC content is increased to 1%, the hardness of the composite increases from 273 HV (Inconel 718) to 302 HV (Table 3). Compared with the as-deposited Inconel 718 superalloy, the tensile strength and yield strength of the 0.5% TiC/Inconel 718 composite increase by 36 and 34 MPa, respectively, but the elongation decreases slightly. When the TiC content is increased to 1%, the average tensile strength, yield strength, and elongation of the 1% TiC/Inconel 718 composite reach 1111 MPa, 781 MPa, and 20.6%, respectively. Compared with the heat-treated 718 superalloy and its composites, the addition of TiC particles also increases the tensile strength and yield strength and reduces the elongation (Fig. 9). Numerous pores and a few cracks are observed in the tensile fractures of the TiC/Inconel 718 composites [Figs. 10(c) and 10(d)]. The high-resolution SEM image and scanning results of the Ti element distribution show that TiC particles are distributed in these pores, which is the reason for the decreased elongation of the composites.

TiC/Inconel 718 composites were manufactured using the LPBF process. The surface-forming quality of the Inconel 718 superalloy and its composites is good, and adding 0.5% and 1% TiC particles can enable control of the increase in the roughness of different surfaces of the composite block to within 5%. Compared with the pore distribution of the Inconel 718 superalloy, the number of pores in the composite with 0.5% TiC particles increases by 37.5%; when the TiC content increases to 1%, the number of pores in the composite increases significantly, and the relative density of the composite decreases from 99.70% (Inconel 718) to 99.32%. The microstructure of the TiC/Inconel 718 composite is similar to that of the Inconel 718 superalloy, and typical epitaxial crystallization is observed, in which TiC particles are uniformly distributed in the matrix of TiC/Inconel 718 composites. With an increase in TiC content, the average Vikers hardness of the composites gradually increases from 273 to 302 HV. Compared with the Inconel 718 superalloy prepared via LPBF, the tensile strength and yield strength of the 1% TiC/Inconel 718 composite increase by 66 and 45 MPa, respectively. The addition of TiC particles improves the tensile strength and yield strength but decreases the elongation.