Lightweight and high-strength textured fibrous Si3N4 3D scaffold seeded with β-Si3N4 particles prepared via freeze casting

• Published in: Journal of materials science & technology Vol. 194; pp. 75 - 86
• Main Authors: Zhi, Qiang, Zhao, Shan, Hou, Baoqiang, Zhang, Nanlong, Li, Feng, Wang, Bo, Yang, Jianfeng
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 20.09.2024
• Subjects: Directional freeze-casting; Fibrous Si3N4 scaffold; High strength; Lightweight; Seeds; Seeds; Fibrous Si3N4 scaffold; High strength; Lightweight; Directional freeze-casting
• ISSN: 1005-0302; 1941-1162
• DOI: 10.1016/j.jmst.2023.12.075

•Fine β-Si3N4 seeds with a high aspect ratio were synthesized via liquid phase sintering.•The directional freezing of α-Si3N4 suspensions with β-Si3N4 seeds addition was employed to fabricate fibrous β-Si3N4 3D scaffolds with textured lamellar walls.•The fibrous grains oriented were synthesized through epitaxial growth on preferentially oriented seed.•The lightweight scaffolds possessed both high porosity and high strength.•The superior compressive strength was attributed to the denser lamellar walls with well-oriented fibrous grains and high-density bridging grains between them. Highly porous Si3N4 ceramics with unidirectionally aligned pore channels are gaining significant attention across various fields due to their outstanding functional capabilities. However, achieving high strength in such unidirectional highly porous Si3N4 ceramics remains challenging. Herein, we design and fabricate a novel β-Si3N4 scaffold composed of directionally aligned lamellar walls with a textured microstructure by directionally freeze casting of α-Si3N4 suspensions with fine elongated β-Si3N4 seeds addition, followed by liquid phase sintering. During the sintering, the scaffold exhibited anisotropic shrinkage, and fibrous β-Si3N4 grains were synthesized through epitaxial growth on the seeds preferentially oriented or the nuclei originated from α-Si3N4 powders, resulting in the grains aligned parallel to lamellar walls and bridged the walls. Seed additions of 7 to 15 wt% were beneficial for the optimized distribution of the two types of β-Si3N4 grains, which contributed to the excellent resistance to bucking-induced fracture for the walls. Compared with other unidirectional porous Si3N4 prepared by freeze-casting in the literature, the Si3N4 scaffold exhibited outstanding compressive strength, ranging from 2.8 to 22.0 MPa, as the porosity decreased from 94.4 % to 88.0 % and the density increased from 175 to 365 mg/cm3. The lightweight and strong Si3N4 scaffolds are promising candidates for engineering applications in harsh environments. [Display omitted]