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.

Introduction: The spatial heterogeneity of reinforcement distribution strongly influences the mechanical response of particle-reinforced metal matrix composites (PRMMCs). However, the respective roles of local reinforcement concentration and network connectivity in deformation and failure remain unclear. Methods: In this study, two-dimensional mesoscale finite element models of SiCp/6061Al composites with identical global SiC volume fraction but distinct cellular architectures were developed. By varying local SiC volume fraction and reinforcement-rich region connectivity, the effects of heterogeneous particle distributions on stress transfer, strain localization, crack initiation and propagation were investigated. Results: The results demonstrate that moderate reinforcement localization enhances tensile strength by improving stress transfer efficiency, whereas excessive localization accompanied by network discontinuity deteriorates macroscopic load-bearing capability. Furthermore, local SiC concentration primarily determines damage initiation through intensified deformation incompatibility, while reinforcement network connectivity governs subsequent crack propagation behavior. A continuous particle-rich framework promotes efficient load transfer but accelerates crack transmission after damage initiation, whereas a disconnected network enhances crack deflection but reduces strengthening efficiency. Discussion: These findings establish a topology-based design principle for heterogeneous SiCp/Al composites, emphasizing that reinforcement connectivity is essential for achieving a favorable balance between strength and damage tolerance.

Ultrasound-assisted metal additive manufacturing (U-FAAM) has emerged as a promising in situ melt-pool regulation strategy for addressing the challenges of conventional metal additive manufacturing, including process instability, defect formation, and microstructural anisotropy. This review systematically summarizes recent progress in contact and non-contact ultrasound-assisted metal additive manufacturing from the perspective of acoustic energy delivery pathways. The interactions between ultrasonic excitation and melt-pool behavior, thermal transport, solidification-front evolution, defect formation, microstructural transformation, and mechanical performance are comprehensively discussed. Contact ultrasound approaches transmit acoustic energy through solid media. Cavitation can occur only when the melt-side acoustic pressure reaches the required threshold; under such conditions, cavitation-associated effects may act with acoustic streaming and inertial melt flow to enhance mixing, grain refinement, and defect mitigation. Non-contact ultrasound approaches provide improved geometric adaptability and mainly influence melt-pool evolution through acoustic streaming and cyclic pressure fluctuations. The relationships among ultrasonic input conditions, melt-side responses, solidification behavior, and final properties are critically analyzed. Furthermore, current limitations associated with acoustic energy attenuation, coupling efficiency, process scalability, and quantitative characterization of ultrasonic effects within the melt pool are highlighted. This review synthesizes current evidence for ultrasound-driven melt-pool control in the investigated fusion-based AM systems, particularly DED/LDED and WAAM, while recognizing the limited evidence for LPBF.

The network architecture has demonstrated considerable potential for enhancing the strength–ductility synergy in metal matrix composites (MMCs). Intuitively, the intersections of network layers are expected to induce a stress concentration, leading to premature brittle fractures. Introducing chamfers to round the network cells may mitigate the local stress concentration and thereby improve elongation. Here, a numerical simulation framework was developed to investigate the effect of chamfering on the mechanical behavior of a three-dimensional (3D) continuous SiC_3D/Al composite with a network architecture. A Voronoi tessellation algorithm was employed to generate the continuous network structural SiC phase. By inducing ductile and brittle damage criterions in the matrix and reinforcement elements, respectively, the mechanical behavior can be predicted via the finite element method (FEM). The predicted mechanical properties reveal an unexpected trend: chamfering results in a simultaneous reduction in both strength (from 367 MPa to 312 MPa) and elongation (from 4.1% to 2.0%). With chamfering, the enlarged intersection of the network layer bears a lower load, whereas the narrower network plates exhibit higher stress concentrations. As a result, the overall load-bearing capacity of the SiC_3D reinforcement decreases monotonically with an increasing chamfer size f. Furthermore, the non-uniform stress distribution promotes the premature fracture of the SiC_3D, which reduces elongation. Additionally, the crack deflection behavior is suppressed in the chamfered models, leading to decreasing energy dissipation. This unanticipated outcome highlights an important architectural design principle: maintaining uniform geometric dimensions is critical for achieving optimal composite performance.

The strength–ductility trade-off limits the wider application of high-strength titanium alloys in aerospace. Here, a new Ti-3.7Al-3V-3Fe-1.7Mo-0.5Cr alloy is designed based on d-electron alloy design theory and molybdenum equivalence, and the dual-phase microstructure is tailored by varying the cooling rate after solution treatment, which governs both the phase fraction and the spatial connectivity of the primary α (α_p) and β phases. In the furnace-cooled (FC) condition, the α_p phase exhibits the highest fraction (76%) and a continuous network with isolated β islands, whereas higher cooling rates (AC and WQ) yield lower fractions (50% and 38%) and a continuous β matrix, confirming that decreasing cooling rate promotes α_p connectivity and β isolation. Consequently, the FC sample achieves a tensile strength of 1250 MPa and a total elongation of 18.4%, significantly higher than those of the AC (14.0%) and WQ (10.0%) samples. This interconnected architecture enhances dislocation storage and work hardening, while enabling effective load transfer and strain compatibility between phases, thereby suppressing strain localization and interface debonding. In situ SEM observations further confirm that high-density α_p/β interfaces, crack deflection, and deformation twinning also play a key role in enhancing damage tolerance. These findings identify phase connectivity as a key microstructural parameter for overcoming the strength–ductility trade-off in α/β titanium alloys.