The Research On Strengthing Of Nb/Nb₅Si₃In-situ Composites

Nb/Nb₅Si₃in-situ composites has been considered as the most potential of hightemperature structural materials because of high melting point, high stiffness, lowdensity and high temperature strength, therefore it is significance of mastering the lawabout the influence of sintering parameter, developing the SPS casting process ofNb/Nb₅Si₃in-situ composites and researching the Strengthening method of Nb/Nb₅Si₃in-situ composites.In this paper the Nb/Nb₅Si₃in-situ composites were successfully fabricated bySpark Plasma Sintering （SPS） technology. The microstructures of the composites wereanalyzed by scanning electron microscopy （SEM）, X-ray diffraction （XRD） andelectron probe microscopy （EPMA）. The microstructure and mechanical properties ofNb/Nb₅Si₃in-situ composites would be influenced by sintering parameter, SPScasting process, alloying and CNTs. The result suggested that:1. The Nb/Nb₅Si₃in-situ composite was fabricated by SPS, it was made up of Nband Nb5Si3, and Nb dispersed and solution in the Nb5Si3. The microstructure andmechanical properties of Nb/Nb₅Si₃in-situ composites would be influenced bysintering parameter. The microstructure would be denser and the hardness would behigher by increased sintering temperature, extended holding time and increased theaxial pressure.2. The eutectic （Nb+Nb5Si3） would be found in Nb/Nb₅Si₃in-situ compositeswhen the SPS sintering temperature above1680℃. The main reason was that thereaction about Nb and Si was very severe, and released large amounts of heat. So thepart temperature in the sample was raised, Nb and Nb5Si3were melted, the eutectic（Nb+Nb5Si3） would be produced in cooling process.3. The microstructure and mechanical properties of Nb/Nb₅Si₃in-situ compositeswould be influenced by Al, Ti, and Y2O3. The hardness of composites would decreasewith the content of Al, Ti increased. The hardness would be increased by themoderate content of Y2O3（less than2wt%）.4. The microstructure and mechanical properties of Nb/Nb₅Si₃in-situ compositesalso would be influenced by alloying elements. The hardness of composites would be increased by W and Cr, and it would be increased first then decreased with the contentof Cr increased. The hardness of composites would be increased with the content of Wincreased. Cr is the most important influencing factor of the hardness of Nb/Nb₅Si₃in-situ composites and then is W, Ti, Y2O3in turn. The optimization alloying schemeof Nb/Nb₅Si₃in-situ composites is Nb-20Si-5Al-15Ti-3Cr-8W-2wt%Y2O3.5. The antioxidation at high temperature of Nb/Nb₅Si₃in-situ composites wouldbe significant affected by alloying. The ant oxidation would be improved by Cr andY2O3. With the content of Cr increased the oxide rate has been decreased first then hasbeen increased. When the content arrived at3at%the oxide rate was the minimum.With the content of Y2O3increased the oxide rate has been decreased. Cr is the mostimportant influencing factor of the antioxidation at high temperature of Nb/Nb₅Si₃in-situ composites and then is Y2O3, Ti, W in turn. The optimization alloying schemeof Nb/Nb₅Si₃in-situ composites is Nb-20Si-5Al-15Ti-3Cr-8W-2wt%Y2O3.6. The hardness of Nb/Nb₅Si₃in-situ composites would be improved by CNTsand it would be increased first then decreased with the content of CNTs increased.When the content of CNTs arrived at2wt%, the hardness of composites was the best.Anew phase Nb4C3would be produced, when the content of CNTs more than2wt%.The hardness of Nb/Nb₅Si₃in-situ composites would be decreased, if do acidtreatment with CNTs.