Wei Wei

Nb-Si-based ultrahigh-temperature alloys are promising structural materials for advanced aero-engines, but their defect behavior is strongly influenced by processing routes. In this study, Nb-Si-based alloys were fabricated by directional solidification (DS), electron beam powder bed fusion (EB-PBF), and directed energy deposition using two deposition strategies (DED and Pull-DED). Their densification, phase constitution, grain structure, silicide morphology, and cracking behavior were systematically investigated. All specimens exhibited relative densities above 99.3%. NbSS and γ-Nb₅Si₃ were detected in all specimens, whereas α-Nb₅Si₃ was observed only in the DS specimen. DS produced a coarse, directionally aligned microstructure, whereas EB-PBF exhibited the most pronounced refinement of both NbSS grains and silicides, with an average equivalent NbSS grain size and average silicide size of 7.65 ± 1.79 μm and 0.87 ± 0.25 μm, respectively. Among the additively manufactured specimens fabricated from the same pre-alloyed powder, EB-PBF and DED produced fine, discrete silicides, whereas Pull-DED exhibited a silicide volume fraction of 44.64% and relatively coarse silicides continuously extending along the deposition direction. Cracks preferentially initiated and propagated within coarse, continuous silicides in the DS and Pull-DED specimens, while the refined and discontinuous silicides in EB-PBF and DED restricted cracking to localized damage. These results demonstrate that processing routes govern cracking behavior by controlling grain structure and the size, morphology, and spatial continuity of silicides, highlighting EB-PBF as an effective route for microstructural refinement and crack suppression in Nb-Si-based ultrahigh-temperature alloys.

The rise of high-performance functional devices has driven significant breakthroughs in various research fields, with ultrafast laser processing offering unprecedented opportunities for advanced device fabrication. This review summarizes recent progress and future prospects for ultrafast laser in fabricating functional optical, semiconductor, and sensor devices. Central to these advances is a deeper understanding of ultrafast laser–matter interaction physics, including nonlinear optical effects, multiphoton ionization, avalanche ionization, and laser-induced plasma dynamics. These phenomena govern carrier excitation, energy deposition, and subsequent structural modification. We further review how such interactions enable controlled refractive index changes, selective ablation, and nanoscale material structuring in photosensitive, dielectric, semiconductor, and metallic substrates. Key applications are then reviewed, including ultrafast laser fabrication of optical devices (e.g., optical waveguide devices, optical data storage elements, optical elements, and artificial compound eyes, integrated photonic devices), semiconductor devices (e.g., semiconductor light-emitting devices, photodiodes, solar cells, and photodetectors), and sensors (e.g., fiber optic sensors, flexible sensors, and biochemical sensors). Recent breakthroughs showcase ultrafast laser-induced precision in device miniaturization, improved optoelectronic characteristics, and integration of complex functions (e.g., topological photonic circuits fabricated via sub-100-nm laser writing, 5D optical data storage in glass with > 1 TB/cm3 density, perovskite solar cells achieving 25.7% efficiency through laser-induced phase engineering, alongside plasmonic biosensors with 100× sensitivity enhancement, and stretchable graphene sensors for wearables). Finally, this review discusses core challenges, such as enhancing the scalability of ultrafast laser processes for industrial-scale production and optimizing laser-material interactions to improve device reliability and performance. Future efforts should address key challenges such as the limited scalability of ultrafast laser processing and the incomplete understanding of laser–matter interactions at ultrafast timescales. Integrating ultrafast lasers with AI-driven control, beam shaping, and advanced materials such as 2D heterostructures may enable smarter and more multifunctional device platforms. A unified theoretical framework is also needed to guide precise and efficient fabrication. These directions highlight critical opportunities for bridging current limitations and enabling transformative advances. While not exhaustive, this review lays a foundation for further research into the transformative potential of ultrafast laser in functional device fabrication.