脉冲激光对激光粉末床熔融 TiB₂/Inconel 718 复合材料微观组织与性能的影响

Objective Ceramic-particle-reinforced metal matrix composites are widely used in aerospace, energy, automotive, and other fields owing to their lightweightness, high strength, thermal-fatigue resistance, thermal-corrosion resistance, and designability. Laser powder bed fusion is an effective method for preparing ceramic-particle-reinforced nickel-based composites. However, the ceramic particles in the formed material are unevenly distributed, thus resulting in the unstable performance of the material. Methods In this study, TiB₂/Inconel 718 composite was selected as the research object. Pulse laser was employed during laser powder bed fusion experiments. By changing the laser power (P), spot spacing (P_d), and exposure time (T_e), the effect of laser-energy density on the forming quality, microstructure, and hardness of the composite material was investigated. The ImageJ software was used to statistically analyze the primary dendrite spacings of the samples. Furthermore, the relationship between the primary dendrite spacing and laser linear-energy density was established. Results and Discussions As the laser volumetric energy density increases gradually, the density of the composite material increases gradually. At low energy densities, the composite material exhibits few fusion defects. After the laser volumetric energy density reaches 165.1 J/mm³, the density stabilizes at 8.0 g/cm³. Under the pulsed-laser mode, the as-deposited microstructure shows columnar dendrites parallel to the build direction, i.e., the high-gradient epitaxial growth effect is dominant. The pulse laser enables a more uniform temperature field of the molten pool, thus rendering the dendrites finer and more uniform. However, under an extremely high energy density, the molten pool is more unstable, thus resulting in disordered dendrite orientations. Conclusions Pulse laser significantly reduces the heat input during the forming process, which causes low fusion levels. As the pulse-laser energy density increases, the low fusion level is mitigated and the sample density increases. Nanosized TiB₂ particles are evenly distributed at the dendrite trunks and interdendritic areas, which is attributed to the stirring effect of the pulse laser on the melt pool. As the laser linear energy density (E_l) increases, the primary dendrite spacing (λ₁) increases linearly based on the equation λ₁ = 0.4896 + 0.0031E_l. Additionally, the hardness of the TiB₂/Inconel 718 composite fabricated via pulsed-laser powder bed fusion can reach 365.8 HV. However, when the laser energy density is beyond the threshold of 240 J/mm³, the microhardness level decreases, which is attributed to the excessive energy input, thus causing the melting of TiB₂ particles and hence the formation of defects.