中文摘要：

采用电弧熔炼法制备了Nb-20Si-10Mo、Nb-20Si-10Mo-3M（M=Cr,Al,Ti）（原子分数）四种Nb-Mo-Si基超高温合金。利用SEM、EDS、XRD等实验技术对铸造合金的相组成与组织形态进行了观察和分析。Nb-20Si-10Mo合金由铌固溶体（NbSS）与βNb5Si3化合物两相构成,其铸造组织包含大量片层状共晶（NbSS-βNb5Si3）组织。少量合金元素Cr（3 at%）能够改变Nb-20Si-10Mo合金的相平衡关系,Nb-20Si-10Mo-3Cr的铸造组织中不仅存在NbSS和βNb5Si3,而且还出现少量Cr2Nb相;而添加合金元素Al、Ti（3 at%）并不改变Nb-20Si-10Mo合金的相平衡关系。添加Cr使NbSS-βNb5Si3共晶组织失去了平直片层特征;Al有利于共晶组织中片层状共晶形成;添加Ti使共晶组织呈现羽毛状特征。合金化使Nb与βNb5Si3的晶格常数发生变化：Nb的晶格常数均变小;Nb-20Si-10Mo-3Cr合金中βNb5Si3的c/a值减小,其它3种合金中βNb5Si3的c/a值增大。

英文摘要：

The alloying effects of 3 at%M （M=Cr, Al, Ti） on the phase equlibria and eutectic morphology of Nb-20Si-10Mo cast alloy were studied by SEM, EDS and XRD. All the studied alloys were prepared by arc melting. The Nb-20Si-10Mo cast alloy contains niobium solid solution （Nbss） and βNb5Si3 two phases. A large volume fraction of lamellar eutectic （Nbss-βNb5Si3） appears in the microstructure. The Cr additions change the phase relationship in Nb-20Si-10Mo cast alloy. A Laves phase of Cr2 Nb precipitates together with Nbss, βNb5Si3 in Nb-20Si-10Mo-3Cr cast alloy, while no third phase was observed in 3 at% Al or 3 at%Ti added alloys. The Nbss-Nb5Si3 eutectic structure loses its straight lamellar characteristic in Cr doped alloy, whereas the lamellar characteristic of Nbss-Nb5Si3 eutectic was enhanced by Al additions. The lamellar eutectic morphology changes to featheriness as a result of Ti additions. The lattice parameters of Nb and βNb5Si3 change with the alloying additions ： The lattice parameters of Nb decrease in all the alloys; the c/a value of βNb5Si3 decreases in Nb-20Si-10Mo-3Cr alloy, while the c/a value of βNb5Si3 increases in the other three alloys.