Research On Structure And Properties Of Alloying Nb/Nb₅Si₃ Composites Doped With Nickel Coated Carbon Nanotubes

Carbon nano-tube reinforced metal matrix composites has become a much discussed topic of today’s research in metal matrix composites.There have been well developed research overseas in this area while the research in China has just started with a major problem that lies in the singularity of preparation methods.A lot more can be further explored.This article studies the influence of nickel plated multi-walled carbon nano-tubes on the properties of composites and the difference between the influence of nickel plated and non-nickel plated carbon nano-tubes.It was done through preparing multiple Nb/Nb₅Si₃ matrix composites reforced by different compositions of nickel plated multi-walled carbon nano-tubes,using spark plasma sintering（SPS）.The article will also elaborate on my exploration on the ball milling process,preparation methods and alloying of composites.The research findings are as followed:1、 The longer the ball milling process on composite powder,the smaller the composite grain,and more damage to the microscopic structure of carbon nano-tube.When the ball milling time reaches 16 h,the carbon nano-tube is almost completely decomposed into elemental carbon and exists within the composite,adversely affecting the performance of composite.If the ball milling time is short,the microscopic structure of carbon nano-tube is protected but the composite grain will become too big,affecting the performance of the composite.A ball milling time of10 h is good enough to evenly separate the carbon nano-tube without causing great damage to its microscopic structure,hence being able to enhance the overall performance of the composite to a better extent.2、Alloying has remarkable influence on the performance of the composite.The addition of over 3wt% Cr will greatly improve the oxidation resistance of the composite with a reaction between the newly added Cr and Nb which gives Cr2 Nb as product.However,when more than 5wt% Cr is added,the reaction will yield a3-phase coexisting structure of Nbss/Nb₅Si₃/Cr2 Nb,which has a low density and thus a negative effect on the performance of the composite.3 、 The addition of 2wt% Al will significantly increase the toughness of composite,to a maximum value of 6.94 Mpa.m1/2.The added Al will react with Nb and Si to form Al3Nb10Si3 which is concentrated between the phase regions of Nb and Nb₅Si₃.This will increase the hardness of Nb₅Si₃ phase.However,an extensive addition of Al will yield AlNb3 which exists within the Nb phase,decreasing thehardness of the Nb phase.The addition of Al will lower the density of the composite as well.The density drops to 6.75g/cm3 when 6wt% Al is added.4、When Ti is added,it will replace Nb to react with Si,giving Ti₅Si₃ and Ti₅Si₄ as products.These compounds exist with the Nb phase.The addition of 1wt% of Ti significantly increases the fracture toughness by 37.6% as compared to a composite without Ti.However,when over 2wt% of Ti is added,the toughness starts to drop.The addition of Ti increases the density/hardness and reduces the porosity of the material.The hardness of the composite is increased by 30% and porosity is decreased by 45%upon the addition of 2wt% Ti.When only 1wt% is added,the density of the composite is 7.4473g/cm3,only a 3.5% increase as compared to a non-Ti composite.