| In the traditional metal matrix composite design process,it is a common way to increase the strength of the composites by adding hard second phases.The addition of the reinforcing phase is often a disorderly and uniform distribution.Although the microstructure of these composites improves the strength,it also greatly reduces the plasticity and toughness,limiting its greater development prospects.However,in nature,after a long evolutionary process,organisms have a more delicate microstructure than the materials designed by humans,such as the nacre.The nacre layer is composed of 95%calcium carbonate and 5%organic medium,and presents a layered stacking structure of calcium carbonate sheets and organic medium.Because of its structure,the nacre layer improves its strength,and its toughness and plasticity are also significantly improved.In order to better reproduce the layered nacre structure on the basis of composites and obtain both better strength and toughness,this paper focused on the bionic nano-layered graphene(reduced graphene oxide,rGO).Based on the preparation of Al-matrix composites,an innovative graphene dispersion method was proposed.That is,the self-assembly behavior of GO on the surface of Al flakes was achieved by modifying the graphene oxide(GO)with silane coupling agent.The main research results of this paper are as follows:(1)Chemical modification of GO using silane coupling agent(3-aminopropyltriethoxy-silane)APS.By heating at 70℃ with magnetic stirring for 4h,APS can be hydrolyzed to produce silanol and occurred dehydration condensation reaction with GO.Through FTIR and XPS analysis,it can be found that C-O-Si covalent bonding occurred between GO and APS.Raman spectroscopy analysis showed that GO was modified with APS.The I_D/I_G ratio increased from 0.89 to 0.95 after the process,indicating that the addition of APS did not significantly affect the original planar structure of GO.(2)Through a series of bottom-up assembly processes,including ball milled Al powder,semi-powder metallurgical blending,drying,thermal reduction and hot-pressing sintering processes,the typical layered structure of the typical nacreous features was effectively replicated.In particular,APS/GO was applied as the reinforcing phase,which was evenly coated on the surface of the Al powder,and the dispersibility was also improved to further strengthen the composites.Through investigating the ball milling process,it was found that the thickness of the Al powder gradually decreased with the continuous increase of the ball milling time,and the shape gradually changed into flakes.In order to make the scale of the microstructure after sintering similar to that of the nacre,and considering the influence of the deformation of the powder in the subsequent hot-press sintering process,the ball milling time for preparing the flake Al powder was optimized at 4 hours.After SEM analysis,it was characterized that APS/GO was tightly coupled with the surface of the flake Al powder,and the number of GO layers was very low,and the dispersibility was good.Without the use of APS modified GO,delamination occurred.(3)The microstructure of the sintered composites basically reproduced the pearl layered stacking structure.Characterized by SEM and TEM,the GO layer and the Al layer were alternately distributed and uniform.The GO and the amorphous alumina formed on the surface of the Al powder were tightly bound,and no obvious defects such as holes appeared at the interface.And the number of GO layers was 10 or less,which showed that the dispersibility after APS modification is good.The test results of the mechanical properties showed that the Vickers hardness of 0.15 wt.%rGO/Al was 40%higher than that of pure Al,which was 33.1±5.8 HV.The compression strength was 58%higher than that of pure Al.The maximum deformation rate was also increased from 41.9%to 51.7%.Through the addition of GO and he nacre-like structure,the strength and structure of the composites were comprehensively improved.This study shows that the chemical modification of GO with silane coupling agent APS can effectively improve the bonding between Al powder and GO,and strengthen the interface relationship between GO and Al powder to form a strong bonding.This design of connecting GO and metal matrix through covalent bonds is a great significance to the design of bionic structure of GO reinforced metal matrix composites.And through the realization of the nacre structure,the strength and structure were greatly improved at the same time,which provides an experimental basis and theoretical basis for the development of high-strength and high-plastic metal matrix composites. |
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