纳米 TiC 含量对激光粉末床熔融 TiC/Inconel 718 复合材料显微组织及力学性能的影响

Objective Laser powder bed fusion (LPBF) technology for fabricating ceramic particle^-reinforced nickel^-based composites is one of the effective methods to enhance the mechanical properties of Inconel 718 alloy. In the reported studies, the ceramic mass fraction is predominantly below 2%. Although some studies have reported TiC mass fraction up to 5% in Inconel 718 alloy, the impact of TiC particles on mechanical properties has still not been thoroughly investigated. Consequently, the contribution of TiC particles to the mechanical properties in high TiC content TiC/Inconel 718 composites remains ambiguous, and the influence of TiC content on the microstructure is not yet well^-defined. Methods In this study, TiC/Inconel 718 composites with TiC mass fraction of 1.5% and 3.0% were prepared by the LPBF technology. The effects of TiC content on the microstructures and mechanical properties of the composites were systematically analyzed. In addition, the effect of TiC particles on the tensile process of LPBF^-TiC/Inconel 718 composites was analyzed. Results and Discussions The thermal conductivity of TiC is significantly higher than that of Inconel 718 alloy, which accelerates the cooling rate of the composite melt pool. This reduces the primary dendrite spacing in the LPBF^-TiC/Inconel 718 composite, leading to a more uniform microstructure. The layered structure becomes less pronounced, and the microstructure is significantly refined. Furthermore, as the mass fraction of TiC increases, the curvature radius of the fusion line in the LPBF^-TiC/Inconel 718 composite gradually increases, and the melt pool becomes flatter. This further promotes the epitaxial growth of dendrites within the melt pool, enhancing the texture strength of the LPBF^-TiC/Inconel 718 composite. The addition of TiC particles significantly improves the mechanical properties of the LPBF^-TiC/Inconel 718 composite and the yield strength increases when the mass fraction of TiC particles increases. The effect of TiC on the yield strength of the LPBF^-TiC/Inconel 718 composite can be analyzed from three aspects: coefficient of thermal expansion (CTE) mismatch strengthening, load strengthening, and fine grain strengthening. The results show that the contribution of these three strengthening mechanisms to the yield strength is positively correlated with the TiC content. CTE mismatch strengthening and fine grain strengthening are the primary contributors to the increase in yield strength of the LPBF-TiC/Inconel 718 composite, while the contribution of load strengthening is relatively minor. Additionally, during the tensile process of the LPBF^-TiC/Inconel 718 composite, TiC particles may debond and spall, forming pits that act as crack initiation sites and propagation paths. This increases the numbers of potential failure initiation points, thereby reducing the elongation of the composite. Conclusions As the TiC content in the composite increases, a notable transformation occurs in the microstructure of the TiC/ Inconel 718 composite. Specifically, the microstructure becomes more uniform, and the distinct layer^-band structure becomes less pronounced and eventually indistinguishable. This uniformity is attributed to the consistent distribution of TiC particles throughout the matrix, which facilitates a more homogeneous microstructure. The addition of TiC particles does not fundamentally alter the as-deposited microstructure of the composite. Instead, it enhances the characteristic of columnar crystal epitaxial growth, which is a key feature of the as-deposited state. This enhancement is observed through the refinement of the microstructure, where the primary dendrite spacing is significantly reduced from 502.2 nm to 355.3 nm. This reduction in dendrite spacing is a direct result of the increased nucleation sites provided by the TiC particles, leading to a finer and more uniform microstructure. Concurrently, the increased curvature radius of the fusion line in the TiC/Inconel 718 composite plays a crucial role in the growth of dendrites within the melt pool. This directional growth is induced by the geometric changes in the melt pool, which in turn enhances the texture strength of the material. The texture strength increases from 4.27 to 12.76, indicating a significant improvement in the material anisotropic properties and overall mechanical performance. Compared to the as-deposited Inconel 718 composite, which serves as a baseline for comparison, the TiC/Inconel 718 composite exhibits a marked enhancement in mechanical properties. This improvement is evident in the increased yield strength, ultimate tensile strength, and hardness of the composite. However, it is important to note that the elongation of each composite is reduced to varying degrees. This reduction in elongation is attributed to the presence of TiC particles, which can act as stress concentrators and potential crack initiation sites. Despite this decrease in elongation, the overall mechanical performance of the TiC/Inconel 718 composite is significantly superior to that of the as-deposited Inconel 718 composite, making it a promising material for applications requiring high strength and durability.