Preparation And Properties Research Of Titanium Matrix Composite Reinforced With In-situ Synthesized Cnts

Titanium matrix composites own the excellent advantages of low density, highspecific strength, good corrosion resistance and high temperature performance, whichenable them to be candidate structural materials for aviation and aerospace. Carbonnanotubes (CNTs) have been considered to be the ideal reinforcement materials formetal matrix composites because of its high specific strength, high specific modulusand excellent comprehensive performance. To bring out the excellent properties,CNTs should achieve a homogeneous dispersal and good interface bonding with thematrix, and avoid reacting with the substrate in the consolidation process. Thus,exploring new preparation methods of CNTs/Ti composites has important theoreticaland practical value for the aerospace application.In this thesis, uniformly dispersed CNTs were in-situ synthesized on Ti powderby chemical vapor deposition method. The influence of the processing parameters,such as the type of catalyst and carbon source gas, synthesis temperature, synthesistime and the ratio of carbon source in the gas mixture on the structure, distribution andproductivity were investigated, and the growth mechanism of CNTs was discussed. Theresults indicate that the CNTs follow a kind of top-growth pattern on the titaniummatrix. Homogeneously dispersed CNTs on the Ti powder surface with uniformdiameter, high purity and crystallization can be obtained by synthesizing at550℃for30min with1.5wt.%-Co as catalyst and C2H2as carbon source, and the volumetricratio of acetylene to argon is1:30. The obtained CNTs-Ti composites powder laid thefoundation for preparation of bulk composite materials with uniformly dispersedreinforcement.The in-situ synthesized CNTs-Ti composite powder was manufactured toCNTs/Ti composites by powder metallurgy method of hot-pressing sintering undervacuum, and the influence of CNTs content and hot-pressing temperature on themicrostructure, mechanical properties and friction and wear properties of compositeswas investigated. It was found that the relative density of composites reached96%ata hot-pressing temperature of900℃, and it implies that composite materials couldform a compact structure at a relatively low temperature by the hot-pressing process. With the increase of hot-pressing temperature in the range of this experiment, thehardness and compressive yield strength of the CNTs/Ti composite increase. Theaddition of CNTs leads to fine grains. However, extra content of CNTs and increaseof high sintering temperature could accelerate the reaction between CNTs and Timatrix to form TiC phase near the particle interface. Relatively high compressiveyield strength was achieved with the increase of CNTs content less than2.0wt.%.The wear resistance performance was improved with the addition of CNTs throughthe mechanism of grain refinement and the carbon layer acting as the lubricant. Thefriction form of the CNTs/Ti composites includes debris wear, abrasive wear andoxidative wear.