Influence Of Soft Phase Size On The Compression Performance And Failure Mechanism Of SiC/Mg Nanocomposites

Magnesium matrix composites have excellent properties such as high strength,light weight and so on.They have broad application prospects in aerospace,automobile industry and electronic products.However,its low strength and weak anti-damage ability limit its wide application in industry.In recent years,more and more researches have begun to improve the properties of materials by introducing ductile phase into the materials.The strength and toughness of the metal matrix composites are improved by using this heterogeneous material design idea.In this thesis,heterogeneous magnesium matrix nanocomposites with different soft phase sizes were prepared by high-energy ball milling combined with vacuum hot pressing.Their microstructure and compression properties were analyzed.Especially,the influence of soft phase size on the failure mode of magnesium matrix nanocomposites was emphatically studied.The main research contents and results are as follows:1.The dense SiC/Mg nanocomposites were prepared by traditional powder metallurgy method.The phase composition of SiC/Mg nanocomposites with different soft phase sizes was analyzed by SEM,EDS,XRD.The results showed that the SiC/Mg nanocomposites with different soft phase sizes had the same phase composition.The XRD results showed that there was no other impurity phase besides a small amount of Mg₂Si and Mg O in the composites.The hard phase of the material was mainly composed of nano-reinforced particles and magnesium,and the soft phase was mainly composed of pure magnesium matrix.The average soft phase sizes of the three SiC/Mg nanocomposites were about 3?m,4.5?m and 16?m,respectively.2.The quasi-static compression properties of SiC/Mg nanocomposites with different soft phase sizes were tested,and the influence of soft phase size on the material properties was analyzed.The mechanical properties of different microstructure in materials were tested and analyzed by nano indentation test.The results showed that the size of soft phase has a significant effect on the compressive properties of the nanocomposites.When the average size of soft phase was reduced from 16?m to 3?m,the compressive strength and ultimate strain of the material were increased by about 26.5%and 40.4%.The elastic moduli of soft and hard phases in the nanocomposites with different soft phase sizes were significantly different.The elastic moduli of hard phases and interface in the nanocomposites with soft phase sizes of 3?m are significantly higher than those nanocomposites with larger soft phase sizes.3.The effect of the size of soft phase on the fracture behavior of SiC/Mg nanocomposites was studied by analyzing the crack propagation behavior and fracture surface of SiC/Mg nanocomposites.The results showed that the size of soft phase significantly affected the fracture mode of the material.In the compression process of SiC/Mg nanocomposites with 3?m soft phase size,the crack was initiated in the hard phase region,then,a large number of microcracks were generated,and the nanocomposite was finally fractured in the form of multiple shear bands.In the compression process of SiC/Mg nanocomposites with 16?m soft phase size,the crack was initiated at the interface between the soft and hard phases,then,it expanded to form the main crack,and the nanocomposite finally broke with an angle of about45°to the direction of the applied stress.The unique hard and soft phase structure significantly improved the toughness of SiC/Mg nanocomposites.A large number of microcracks generation during compression were the main reason for the relatively better toughness of SiC/Mg nanocomposites with small soft phase size.