University of Northwestern – St. Paul

Heterogeneous alloy designs can significantly enhance the mechanical properties of metallic materials through synergistic effects. In this work, the cold spray additive manufacturing (CSAM)-assisted brazing is proposed to significantly improve the mechanical properties of Cf/C and superalloy joint. The CSAM process promotes the atomic diffusion and metallurgical reaction between the interlayer and superalloy substrate. The findings indicate that the diffusion of Fe, Cr, Ni and Ti within brazing seam promotes the formation of a novel dual-phase heterogeneous structure, comprising a Cr-rich σ phase and a Ni3Ti phase. The σ and Ni3Ti dual-phase heterogeneous structure significantly improves shear strength through a synergistic strengthening mechanism, achieving an effective combination of strength and toughness. The ductile Ni3Ti phase enhances the deformation capacity, while the hard σ phase serves as a continuous barrier to dislocation movement, thereby significantly enhancing the mechanical properties of the brazed joint. The highest shear strength of the Cf/C and superalloy brazed joint reaches 20.9 MPa using a CSAM NiTi75 interlayer, compared to only 6.1 MPa for the joint brazed with conventional NiTi75 powder filler. This work demonstrates the significant potential of CSAM-assisted brazing to enhance the mechanical properties of brazed joints, offering a novel approach to directly prepare brazing interlayers from metal powders.

The work devises a novel velocity-prediction lightweight diffusion model (VPLDM) for three-dimensional aircraft aerodynamic inverse design under high-dimensional variable constraints. The model uses a lightweight diffusion modeling paradigm based on a multilayer perceptron, and reconstructs the noise predictions of traditional diffusion models into velocity predictions, which improves the design efficiency and design accuracy. Trained on a dataset of three-dimensional aircraft, the model is able to generate new samples from random vectors that meet the constraints of specific aerodynamic performance indicators. VPLDM achieves higher design accuracy while demonstrating approximately 4 times higher sampling efficiency compared to Denoising Diffusion Probabilistic Model. The model can also generate aircraft schemes with significantly different geometries in the design space, which confirms the typical non-uniqueness of solutions to the aerodynamic inverse design problem for aircraft. All generated shapes satisfy the desired aerodynamic characteristics, demonstrating the role of VPLDM in the three-dimensional aircraft aerodynamic inverse design.

Designing precipitation-strengthened FCC/B2 dual-phase high-entropy alloys promotes the development of structural materials with high mechanical performance and lower density. In the present work, Ti and Ta were utilized as alloying elements in a Ni43.9 Co19 Cr10 Fe10 Al15 Mo2 B0.1 alloy to concurrently enhance the precipitation strengthening in both the FCC and B2 phases. In the FCC phase, the alloying elements increased the volume fraction of L12 precipitates and anti-phase boundary energy, thereby enhancing the precipitation-strengthening effect. In the B2 phase, the alloying elements promoted the formation of FCCstructured precipitates with refined inter-precipitate spacing and thus improved the Orowan strengthening contribution. With the harder B2 phase, the more significant hetero-deformation-induced hardening enhanced the alloy strain hardenability. Although ductility decreased, the continuous stacking fault glides and phase transformations in the FCC-structured precipitates contributed to the strength-ductility synergy by preventing intragranular cracking and mitigating crack propagation in the B2 phase. These findings provide valuable insights for the future design and development of precipitation-strengthened FCC/B2 dual-phase high-entropy alloys. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Ceramifiable FRP composites have attracted considerable attention due to their exceptional properties and extensive potential applications as thermal protection materials. However, the service temperature significantly affects their mechanical properties and failure behaviors. To date, systematic studies on the internal damage evolution and failure mechanisms of ceramifiable FRP composites under mechanical loading at elevated temperatures are lacking. In this study, in-situ synchrotron X-ray computed tomography (XCT) is used to obtain the 3D morphology evolution of ceramifiable FRP composites under compressive loading from room temperature to 10 0 0 degrees C for the first time. The internal damage was classified into four kinds (including warp-weft fiber debonding, matrix crack, interfiber failure, and delamination), and identified by a convolutional neuronal network model. At the same time, a detailed and in-depth study was conducted on the internal damage evolution of these four kinds of cracks with the changes in load levels and temperatures. It is found that the main damage types and degrees are highly correlated with temperature. Additionally, the evolution of 3D strain was calculated by digital volume correlation technology, and the correlation between the high-strain region and the fracture location was analyzed. This study provides a new and practical way to quantitatively analyze and automatically track the micro-crack evolution behavior inside ceramifiable composites in 3D view. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

This study deciphered the influence of lamellar alpha ( alpha l ) colony parameters on impact toughness of alpha+ beta titanium alloy with lamellar microstructure. alpha+ beta titanium alloy Ti-5Al-7.5V-0.5Mo-0.5Zr-0.5Si was beta treated and cooled under different cooling rates to obtain alpha l colony with diverse morphology and size. Unotch Charpy impact test revealed that the impact toughness increased with decreased cooling rate and consequent alpha l colony coarsening. Impact load-displacement curves demonstrated that alpha l colony coarsening simultaneously enhanced both impact crack initiation energy and crack propagation energy. In the crack initiation region near U-notch, slip trace analysis indicated that coarse alpha l colony extended dislocation mean free path and triggered multiple slips, which facilitated plasticity prior to U-notch cracking and enhanced Wi . Furthermore, as evidenced by Focus Ion Beam-Transmission Electron Microscopy, the nucleation of {101 2} <1 011 > twin in coarse alpha l colony mitigated deformation heterogeneity, acted as prismatic slip pathway, and provided sustainable < c + a > dislocation sources, thereby further delaying U-notch crack initiation and enhanced Wi . Conversely, fine alpha l colony restrained dislocation mobility and inhibited twin nucleation, leading to inferior U-notch plasticity and resultant low Wi . From U-notch cracking to final fracture, the sustained crack blunting due to substantial plastic deformation of coarse alpha l along the crack path, as well as crack deflection and branching between adjacent coarse alpha l colonies, synergistically enhanced Wp . Conversely, fine alpha l colony impaired the plasticity along the crack path and restrained crack deflection, which was inconducive to Wp . In summary, alpha l colony coarsening played a crucial role in activating multiple toughening mechanisms during both crack initiation and propagation to achieve desirable impact toughness in alpha+ beta titanium alloys with lamellar microstructure. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.