Fabrication And Mechanical Properties Of Mg-based Composites Reinforced By SiC Whisker Scaffolds With Three-Dimensional Interpenetrating-Phase Architecture

The quest for more-efficient energy-related technologies necessitates the development of lightweight,high-performance structural materials with exceptional strength and toughness.Mg and Mg alloys,as important lightweight metal materials,have attracted great attention due to their excellent properties,such as low density,high specific strength and good damping properties;however,their extensive applications are limited by their low strengths.The strengths of Mg and Mg alloys can be effectively enhanced by introducing reinforcement phases into their matrices,i.e.,via fabricating Mg-based composites.In this regard,silicon carbide whisker(SiCw)is attractive for incorporating with Mg because of its exceptional mechanical properties and a large aspect ratio.Nevertheless,the mechanical properties of Mgbased composites demonstrate a strong dependence on their microstructures.Indeed,many natural materials like bone and nacre have highly sophisticated structures with complex hierarchical designs and exhibit properties far exceeding those expected from a simple mixture of their components.Here,new Mg-based composites reinforced by SiC whisker scaffolds with threedimensional interpenetrating-phase architecture were fabricated through pressureless infiltration of the melt of pure Mg or AZ91D-Mg alloy into the porous scaffolds of SiC whiskers.These whiskers were preferentially stacked in-plane within lamellae in the composites using gravity-assisted sedimentation and subsequent densification during the fabrication process.The microstructures and mechanical properties of the composites,particularly their fracture toughness,were characterized and analyzed.The wettability between the SiC whisker scaffolds and the melt was improved by introducing surface reactions between them which was accomplished by a preoxidation treatment of the scaffolds before infiltration.The pre-oxidation temperature was adjusted to ensure an adequate filling of the scaffolds without voids while avoiding the formation of excessive reaction products.The resulting composites exhibited a high hardness and flexural strength with some extent of fracture toughness as evidenced by stable crack propagation with rising R-curve behavior.In comparison to the use of pure Mg as a matrix,the composites infiltrated with AZ91D-Mg alloy contained a larger amount of coarsened precipitates,and thereby exhibited apparent brittleness despite an increase in the hardness and strength.This study may provide useful guidance for optimizing the fabrication and mechanical properties of Mg-based composites reinforced by SiC whiskers,thereby promoting their potential applications as lightweight structural materials.