Compression And Fracture Behavior Of Hierarchical Magnesium Matrix Nanocomposites Reinforced With SiC Particles

Particle reinforced metal matrix composites are widely used in aerospace industry,military equipment and electronic device because of their excellent properties.However,in cases,the application of particle reinforced metal matrix composites is limited by their inverse relationship between strength and toughness.In other words,its toughness decreases with the increase of strength.The study found the SiCp/Mg nanocomposites with designed hierarchical structure have good strength and toughness.It perfectly solved the problem of matching the strength and toughness of particle reinforced composites.However,the compression and fracture behaviors of SiCp/Mg nanocomposites with hierarchical structure have not been studied carefully.In this paper,the microstructure deformation mode,fracture characteristics and toughening mechanism of SiCp/Mg hierarchical nanocomposites was investigated.The main work are as follows:1.We successfully prepared dense and impurity free composite materials by powder metallurgy method.The microstructures characterized by XRD,SEM and TEM.It is determined that the material has obvious hierarchical structure,including soft regions as the dispersed phase and hard regions as the continuous phase.2.The SiCp/Mg nanocomposites with hierarchical structure are tested by quasistatic compression,dynamic compression and bending methods.In general,the SiCp/Mg nanocomposites with hierarchical structure maintain good toughness while improving the strength of the matrix.Its strength and toughness match better comparing with the SiCp/Mg nanocomposites with uniform distribution.3.The deformation,failure,crack propagation mode,and fracture mode of SiCp/Mg nanocomposites with hierarchical structure under compression and bending were characterized and analyzed.As a result,the distribution of the soft phase after deformation in SiCp/Mg nanocomposites shows orientated distribution.The fracture mode is identified as brittle fracture in hard phase and plastic fracture in soft phase simultaneously.The toughening mechanisms under the quasi-static compression include randomly distributed microcracks within the material caused by hierarchical structure,microcrack bridging,and inhibition of crack propagation by soft phase.The toughening mechanism of the dynamic compression is mainly attributable to the adiabatic effect of high strain rate,which causes local melting in the hierarchical structure of the material,thus increasing the plasticity of the material.The toughening mechanisms under bending consist of crack deflection,interfacial debonding,crack bifurcation,crack convergence and blunting of crack tip,thus increasing the fracture toughness and damage tolerance of the material.