The Research Of Improving Antioxidation At High Temperature Of Nb/nb5si3in-situ Composite

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, however, it has not been use widely as hightemperature structural materials for its poor performance about antioxidation at hightemperature. So the object of this subject is researching to improve the antioxidationat high temperature of Nb/Nb5Si3in-situ composites.In this paper the Nb/Nb₅Si₃in-situ composites were successfully fabricated bySpark Plasma Sintering （SPS） technology. The antioxidation at high temperature isimproved by alloying. The material oxidation rate is obtained by circular oxidationexperiment. The microstructures and their antioxidation mechanism of the compositeswere analyzed by optical microscopy （OM）, scanning electron microscopy （SEM）,X-ray diffraction （XRD） and electron probe microscopy （EPMA）. The main purposeof this paper was that researched the influence of alloying elements and exploredthe mechanism about Nb/Nb5Si3in-situ composites.The following results have been obtained by the research:1. The antioxidation at high temperature of Nb/Nb5Si3in-situ composites havebeen improved by Al element. With the content of Al increased the oxide rate hasbeen reduced and when the content arrived at15at%the oxide rate has down to1/11of original composites. The Al₂O₃has been found in the oxide scales because of Alelement. Because the Al₂O₃could be formed continuous oxide layers, theantioxidation at high temperature of Nb/Nb₅Si₃in-situ composites is improved.2. The antioxidation at high temperature of Nb/Nb₅Si₃in-situ composites alsocan be improved by Ti element. With the content of Ti increased the oxide rate hasbeen reduced and when the content arrived at24at%the oxide rate has down to1/6.5of original composites, at800℃. TiO₂and Ti₂Nb₁0O₂9have been found in the oxidescales because of Ti element. They could form the protection scales and theantioxidation at high temperature of Nb/Nb₅Si₃in-situ composites is improved.3. The antioxidation at high temperature of Nb/Nb₅Si₃in-situ composites wouldbe significant affected by Cr element. With the content of Cr increased the oxide rate has been decreased first then has been increased when the composites were oxidizedat800℃and1100℃. When the content arrived at3at%the oxide rate was minimumand the content arrived at5at%the oxide rate was maximum.4. The antioxidation at high temperature of Nb/Nb₅Si₃in-situ composites wouldbe influenced by W element. With the content of W increased the oxide rate has beenincreased first then has been decreased when the composites were oxidized at800℃and when the content arrived at8at%its antioxidation was the best. With the contentof W increased the oxide rate has been decreased first then has been increased whenthe composites were oxidized at1100℃and when the content arrived at5at%itsantioxidation was the best.5. The antioxidation at high temperature of Nb/Nb₅Si₃in-situ composites wouldbe influenced by Y₂O₃. With the content of Y2O3increased the oxide rate has beendecreased when the composites were oxidized at800℃and when the contentarrivedat2wt%the oxide rate was the minimum. With the content of Y₂O₃increased theoxide rate has been increased first then has been decreased when the composites wereoxidized at1100℃and when the content of Y2O3arrived at2wt%the oxide rate wasthe maximum.6. Cr is the most important influencing factor of the antioxidation at hightemperature of Nb/Nb₅Si₃in-situ composites and then is W, Y₂O₃, Ti in turn. Theoptimization alloying scheme of Nb/Nb5Si3in-situ composites is22at%Ti,3at%Cr,8at%W,2wt%Y₂O₃when the composites were oxidized at800℃. Cr also is the mostimportant influencing factor of the antioxidation of composites and then is Y₂O₃, Ti,W in turn. the optimization alloying scheme of Nb/Nb5Si3in-situ composites is20at%Ti,3at%Cr,5at%W,2wt%Y₂O₃when the composites were oxidized at1100℃.7. Al, Ti and Cr were added into Nb/Nb5Si3in-situ composites in order to getdense and integral oxide scales. The reaction about Nb and O would be cut off bythose alloying, because they could interaction with O and increase the number ofsolute. The adhesion and the integrity of oxide scales would be improved by addingY2O3into Nb/Nb₅Si₃in-situ composites. The appearance of microstructure would bechanged, the niobium particles would be refinement and the hardness of Nb/Nb₅Si₃in-situ composites would be improved by W, because it could dispersed and solutionin the composites.