Research On The Preparation And Mechanical Properties Of Carbon Nanotubes Reinforced Composites

Carbon nanotubes (CNTs) are ideal reinforcement for polymer or metal matrix composites due to their outstanding mechanical, thermal, optical and electrical properties. Eopxy and Ti6A14V were chosen for matrix in this study, multi-walled carbon nanotubes (MWCNTs) were reinforcement. The effect of content, length and dispersion of MWCNTs on the mechanical properties and fracture behavior were studied. And based on the experimental results, a modified Halpin-Tsai model was obtained. Epoxy and Ti6A14V were chosen as matrix. MWCNTs reinforced hollow glass microspheres (HGMs)/epoxy syntactic foam was prepared, and the effect of MWCNTs on density, compression properties and water absorption of syntactic foam were investigated. TiC/Ti6A14V composites were fabricated by using in situ casting method, MWCNTs as carbon sources. The effect of MWCNTs on TiC morphology, microstructure, mechanical properties and fracture behavior of composites were studied, the reinforcement mechanism was also discussed.The results of the study are showed bellow:1. Both the modulus of MWCNTs/epoxy have the peak value when the content of MWCNTs is 0.3wt.%. But with increasing the content of MWCNTs, the dispersion is getting worse, aggregation of MWCNTs will result in decrease of mechanical properties. Longer MWCNTs are beneficial to effective loading transfer, which can improve the mechanical properties of MWCNTs/epoxy composites. Good dispersion of MWCNTs can be achieved under ultrasonication treatment because of the cavitation effect, especially when the content of MWCNTs is high. The reinforcement mechanisms of CNTs mainly are CNTs bridging and crack deflection.2. A modified Halpin-Tsai model was obtained base on the literature. The value of the semi-empirical parameter p, related to the degree of CNT aggregation, increases with increasing the content of CNTs. The differences between the predicted value and experiment results of modulus of CNTs/polymer composites are around ±5%. Even if the content of CNTs is high, the differences are only about ±10%. If the polymer matrix is brittle materials, and we assume that the strain does not change after adding CNTs, and the stress-strain curve of CNTs/polymer composites is linear, the modified Halpin-Tsai model can also be used to predict the fracture toughness of CNTs/polymer composites according to the Griffith theory. The predicted value of fracture toughness of CNTs/polymer composites fit the experimental data well, the difference are about ±10%。3. Adding 0.3wt.% MWCNTs does not change the density of HGMs/epoxy syntactic foam much. When the content of HGMs is 70vol.%, the theoretical density is much higher than real density due to the higher viscosity of HGMs/epoxy mixture and voids generated during preparation of specimens. The compression strength of HGMs/epoxy syntactic foam improves by 17-25% after adding MWCNTs, which is attributed to the blocking and bridging cracks of MWCNTs. Adding MWCNTs and increasing the content of HGMs will both decrease the water absorption of HGMs/epoxy syntactic foam because of the hydrophobicity of MWCNTs and HGMs. But the voids defects will lead to the water absorption increase.4. TiC reinforced Ti6A14V composites can be fabricated by using in situ casting method through adding MWCNTs as carbon sources. MWCNTs will decrease the grain size, and also change the solidification process of composites. The formation of primary dendritic TiC was restrained, and the TiC morphology changes from dendritic to finer equiaxed shape. The tensile strength of TiC/Ti6Al4V composites by adding MWCNTs improves by 10.6%, and the strain decreases from 1.41% to 1.04%. Most of TiC particles are uniform and discountinuously distributed on the grain boundary. The Ti6A14V matrix is riven by TiC particles, so the fracture behavior is typical brittle intergranular fracture because the cracks propagate along the grain boundaries of composites. The pulling-out and rupture of TiC particles are considered as the major reason which cause the improvement of mechanical properties of the composites.