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Preparation and characterization of high damage-tolerance nacre-inspired magnesium alloy matrix composites with high carbon nanotube contents

Sun, Xun, Guo, Rui-Fen, Shaga, Alateng, Hu, Zhi-Jie, Shen, Ping, Zhang, Zhi-Qiang, Jiang, Qi-Chuan
Carbon 2020 v.162 pp. 382-391
alloys, carbon nanotubes, magnesium, magnesium oxide, pressing, silica
A nacre-like magnesium matrix composite with high carbon nanotube (CNT) contents (up to 4.40 wt%) was successfully prepared under the combined effects of bidirectional freeze casting, pressureless infiltration, and hot pressing. The bidirectional freeze casting was carried out to fabricate large-scale parallelly layered CNT scaffolds. The spontaneous infiltration of an AZ91 magnesium alloy was achieved using nano-silica as the wetting promoter, and MgO and Mg₂Si (reaction products) provided the strength of the as-synthesized composites. Furthermore, the hot pressing increased the average thickness ratio of reinforcing phase/alloy layers in the AZ91/CNT composites from 0.89 (before hot pressing) to 1.46 (after hot pressing) and also significantly improved the specific strength from 142.3 MPa/(g⋅cm⁻³) to 158.7 MPa/(g⋅cm⁻³) without sacrificing the specific toughness ((17–18) MPa⋅m¹/²/(g⋅cm⁻³)). The resultant composites were mainly strengthened by CNTs, reaction products, and the strong interfacial bonding between CNTs and the Mg matrix. The key toughening mechanisms for the as-prepared composites were crack deflection, branching, and CNT pull-out. This study provides a new idea for the economical and efficient preparation of lightweight and damage-tolerant composites with high CNT contents.