Xiaonan Lu

Titanium matrix composites (TMCs) possess excellent properties, which are widely applied in various high-end fields. An ultrafine multi-scale network structure may further enhance the TMCs. Then, the application potential is widened. Here, the in situ synthesized TC4-B-Si composites were prepared by selective laser melting technology, to achieve ultrafine microstructure by inducing ultra-rapid heating/cooling process. The preparation process–structure–performance relationships were investigated. It was found that an appropriate laser energy density leads to high-density TMCs with stable molten pools and good interlayer bonding. With the decreasing energy density, the in situ generated TiB network structure is refined from the sub-micron scale to the nano-scale. The most Si atoms are supersaturated solid-dissolved in the titanium matrix. In addition, the TiB distribution becomes heterogeneous. Due to the co-effect of grain refinement and reinforcement distribution, the microhardness shows a rising and then falling trend, with decreasing energy density. With a good balance of these two factors, the maximum value of microhardness reaches 454 HV. Therefore, controlling process parameters is a feasible way to achieve multi-structures, and thus enhanced properties. This method is expected to be used on various lightweight and wear-resistant structural components.

Finite element method (FEM) is a powerful tool to predict the properties and reveal the mechanisms of metal-matrix composites (MMCs) with very complex architectures and novel microstructures. Recent studies have demonstrated the effectiveness of network reinforcement architectures on simultaneous strengthening and toughening. Here, as a key factor in modeling network architecture, the critical microstructure size was studied via FEM. We found that a critical microstructure size of 23 [ ]m (cell count [ ]20) existed in the FEM model, beyond which the crack deflection may be feasibly induced from particle-rich to matrix regions, leading to crack propagation in the ductile matrix cells and thus high strength and elongation. While, with cell size 20–23 [ ]m in SiC/6061Al model, the composite strength and elongation remained intact, implying that the maximal microstructure size is 23 [ ]m for effective network architecture simulations.

Recent works have experimentally proven that metal matrix composites (MMCs) with network architecture present improved strength–ductility match. It is envisaged that the performance of architecturally designed composites is particularly sensitive to reinforcement strength. Here, reinforcing particles with various fracture strengths were introduced in numerical models of composites with network particle distribution. The results revealed that a low particle strength (1 GPa) led to early-stage failure and brittle fracture. Nevertheless, a high particle strength (5 GPa) delayed the failure behavior and led to ductile fracture at the SiC/Al–Al macro-interface areas. Therefore, the ultimate tensile strengths (UTS) of the network SiC/Al composites increased from 290 to 385 MPa, with rising particle strength from 1 to 5 GPa. Based on the composite property, different particle fracture threshold strengths existed for homogeneous (~2.7 GPa) and network (~3.7 GPa) composites. The higher threshold strength in network composites was related to the increased stress concentration induced by network architecture. Unfortunately, the real fracture strength of the commercial SiC particle is 1–2 GPa, implying that it is possible to select a high-strength particle necessary for efficient network architecture design.