Preparation And Mechanical Properties Of CNT-CF/LAS Multiscale Reinforced Ceramic Matrix Composites

In this paper,the chemical vapor deposition method,nickel acetate was used as the catalyst precursor,and cyclohexane was used as the gas phase carbon source.The carbon nanotubes(C_NT)were synthesized in situ on the surface of continuous carbon fiber?C_F?,and more C_NT-C_F was produced.Grade reinforcement;explore the growth rule of carbon nanotubes by controlling catalyst concentration and growth temperature;further study the growth mechanism of carbon nanotubes;composite C_NT-C_F multiscale reinforcement prepared under different conditions to lithium aluminum silicon C_NT-C_F/LAS composites were successfully prepared in?LAS?ceramic matrix;the effects of multiscale reinforcement on the mechanical properties and failure modes of the composites were investigated.Mainly get the following research results:The concentration of the catalyst solution has a great influence on the growth of carbon nanotubes.The suitable catalyst concentration is 2 wt%.Under this catalyst concentration,the carbon nanotubes are uniformly distributed;the growth temperature has a great influence on the morphology of the carbon nanotubes.: The growth temperature of 500 °C-600 °C,the length of carbon nanotubes is the shortest,the thickness of carbon nanotubes is about 200-400 nm,and the defects are less;the growth temperature of 700 °C-800 °C,carbon nanotubes The layer thickness reaches 2-3 ?m,and the bamboo-like and bead-like morphology begins to appear in the nanotubes.At the growth temperature of 900 °C,the length distribution of the carbon nanotubes is uneven,and a large number of bamboo and rosary-like shapes appear.At the same time,the phenomenon of curling is more serious,and the carbon nanotube layer is about 3 ?m.The growth mechanism of carbon nanotubes is a gas-solid-solid mechanism at low temperatures,a gas-liquid-solid mechanism at high temperatures,and a top-end model in the growth mode.The prepared carbon nanotubes are multiwalled carbon nanotubes,which affect the growth rate of carbon nanotubes.The direct factors of morphology are temperature and carbon source atmosphere.The unstable local atmosphere will cause the bamboo tube to appear bamboo,beaded and curled.Using cyclohexane as carbon source,a layer of pyrolysis is prepared on the surface of carbon fiber.Carbon?Py C?,this layer of pyrolytic carbon has little effect on the growth of carbon nanotubes.The mechanical properties of C_NT-C_F/LAS composites prepared by C_NT-C_F have not been improved but have decreased.The main reason for the performance degradation is the introduction of nickel,etching carbon fiber at high temperature,causing original cracks on carbon fiber,causing rapid breakage of carbon fiber;C_F?P?/LAS composites prepared by C_F?P?,bending properties It has increased by 19% to 505 MPa,and it does not break immediately at the maximum load during the fracture process,showing a certain toughness.The fracture toughness and fracture work of the composite are improved,and the fracture toughness and fracture work are increased respectively 17% and 34%,reaching 8.8 MPa?m1/2 and 3.5 k J?m-2.The main reason for the strengthening is that after the introduction of pyrolytic carbon,the crack can propagate at the interface between the pyrolytic carbon layer and the carbon fiber,absorbing more fracture work;C_NT-C_F?P?/prepared by C_NT-C_F?P?.The flexural strength of LAS composites reached 602 MPa,and the fracture toughness and fracture work reached 10.7 MPa?m1/2 and 4.6 k J?m-2.The C_NT/LAS layer present in the C_NT-C_F?P?/LAS composite can deflect the crack by the carbon nanotubes,which improves the mechanical properties of the material;the strength of the C_NT/LAS layer for material properties is related to the thickness of the C_NT layer.The thicker the C_NT layer,the larger the thickness of the C_NT/LAS layer,the better the strengthening effect,and the morphology of the carbon nanotubes has little effect on the performance.