Study On The Preparation And Performance Of Carbon Nanotubes Reinforced Alumina Matrix Composites

Carbon Nanotubes?CNTs?is regarded as a good reinforcement for ceramic matrix composites,for the excellent electrical,thermal,mechanical properties and good chemical stability.The enhancement effect of CNTs can't reach the expectation in theory.It was affected by many factors such as the dispersion of carbon nanotubes in the ceramic substrate,the interface bonding strength between the CNTs and the substrate materials and the structural integrity of CNTs.Therefore,how to get the CNTs dispersed homogeneously in the ceramic at the same time keep the structure of CNTs in the process of preparation,and improve the interface bonding strength,is the key to improve the CNTs reinforced effect.In this study,CNTs reinforced alumina matrix composite materials with excellent mechanical properties were prepared by molecular level mixing method and sintered by hot press.Firstly CNTs were dispersed in aluminum salt solution,then through adjustment of PH value,make the solution system to form a precipitate and CNTs were coater by it.then after the suction filter,washing and drying,CNTs/hydrated alumina composite powder was prepared.Finally,after presintering and hot-pressing sintering CNTs reinforced alumina matrix composites were prepared.The results showed that with the addition of NH₃.H₂O precursor AlCl₃·6H₂O turned to hydrated alumina,Generated hydrated alumina coated CNTs or formed tiny particles in suspension,Then,they were filtered and rinsed,the filter cake was dry in different ways.The powder prepared by spray drying was better than other drying methods.The powder has high degree of sphericity and the diameter of the powder was 0.5⁵um,most of CNTs was coated in spherical particles,a small number of CNTs exposed on the surface of particles.No obvious reunion CNTs or free from the particles CNTs was found,After presintering,the crystal water was removed,hydrated alumina turn to?-Al₂O₃.With the reduce of volume,so the composite powder got some certain pore in the surface.The powder preparation method used in this study could reduce the destroy of the structure of the CNTs,the dispersion of CNTs will be better too.Hot press was used in this paper to sinter composite powder and prepare the composite block,the mechanical properties relative density,hardness,bending strength and fracture strength was measured,Raman spectroscopy was used to detect the integrity of the structure of CNTs,FESEM was used to analyze the microstructure structure of the composite.After hot press sintering at1500?,the mechanical properties of composites with different CNTs concentrations were researched.With the increase of content of CNTs the bending strength and fracture toughness gradually increase,however,relative density and hardness decreased a little bit,On the addition of 2wt%of CNTs the flexural strength and fracture toughness reached 498.3MPa and 5.69 MPa·m^1/2?55.3%and 84.7%higher than pure Al₂O₃?,respectively.when the content of CNTs is more than 2wt%,the mechanical properties of composite materials falling fast,at the same time,other mechanical properties fell too.2wt%content of CNTs composite powder which sintering at 1700?get higher relative density and hardness than sintering at 1500?,but there is no increase on the bending strength and fracture toughness,reduced by 3.0%and 0.4%respectively.Through the analysis of Raman spectra,proved that the CNTs structure remains relatively complete in this experiment.The improved mechanical properties of the composites were analyzed according to the microstructure of the composites.Through the analysis of the CNTs pull out form,get the conclusion that there are some bonding between CNTs and the substrate but not too much.At the same time we found the evidence of the strengthening mechanism such as the pull out of CNTs the bridge of CNTs,and the crack deflection mechanism.The improvement of mechanical properties is the achievement for the work together of these three mechanisms.