The Nb 10Si (mole fraction, %) alloy was fabricated using the vacuum arc melting method and heat treated at 1850?℃ and 1?550?℃ for 2～100?h in Ar atmosphere. The microstructure of the alloy has been investigated usi...The Nb 10Si (mole fraction, %) alloy was fabricated using the vacuum arc melting method and heat treated at 1850?℃ and 1?550?℃ for 2～100?h in Ar atmosphere. The microstructure of the alloy has been investigated using X ray diffractometry(XRD), scanning electron microscopy (SEM) equipped with X ray energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM). The results show that 1?550?℃, 100?h is an optimum heat treatment condition to acquire the equilibrium Nb+Nb 5Si 3 two phase microstructure. The microstructure of Nb 10Si alloy in the as cast condition consists of continuous Nb 3Si matrix and dispersed Nb particles, which implies that the alloy is in the metastable equilibrium state. In the case of 1?850?℃, 2?h heat treatment the Nb particles are coarsened evidently. However, in the heat treatment condition of 1?550?℃ for 25～100?h the growth of Nb particles is unconspicuous. After heat treated at 1?550?℃, Nb 3Si phase transforms into the equilibrium Nb 5Si 3 and Nb phase with the increase of heat treatment time gradually. TEM observations reveal that the interface of Nb phase and Nb 5Si 3 phase is clean and some twins with about 10?nm in width are found.展开更多
Dense Nb/Nb5Si3 composites were fabricated via spark plasma sintering technology using Nb, Si, and Al elemental powders as raw materials. The microstructttres of the synthesised composites were analyzed through scanni...Dense Nb/Nb5Si3 composites were fabricated via spark plasma sintering technology using Nb, Si, and Al elemental powders as raw materials. The microstructttres of the synthesised composites were analyzed through scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. The results show that the composites consisted of residual Nb particle phase and Nb5Si3 phase. The microstructure of the Nb/ Nb5Si3 in situ composites was evidently affected by Al addition, which prompted the formation of the Al3Nb10Si3 phase. In addition, the Rockwell hardness of the composites decreased with the increase in AI additions. The Rockwell hardness of Nb-20Si is 60HRC, which decreased to approximately 52.7 HRC when the Al content increased to 15 at%. The oxidation resistance of the Nb/NbsSi3 in situ composites significantly improved with the increase in Al addition.展开更多
基于第一性原理的密度泛函理论(DFT)赝势平面波方法,采用局域密度近似,计算了α-Nb_5Si_3,β-Nb_5Si_3和γ-Nb_5Si_3的电子结构、态密度以及布居数和力学性质.研究表明:三种不同结构的Nb_5Si_3形成能均为负值,均为热力学稳定的,其中α-N...基于第一性原理的密度泛函理论(DFT)赝势平面波方法,采用局域密度近似,计算了α-Nb_5Si_3,β-Nb_5Si_3和γ-Nb_5Si_3的电子结构、态密度以及布居数和力学性质.研究表明:三种不同结构的Nb_5Si_3形成能均为负值,均为热力学稳定的,其中α-Nb_5Si_3最稳定.α-Nb_5Si_3、β-Nb_5Si_3和γ-Nb_5Si_3的体积模量分别为:192.3 GPa、188.6 GPa和185.9 GPa;剪切模量分别为130.9 GPa、111.4GPa和24.4 GPa.其中α-Nb_5Si_3具有最高的体积模量和剪切模量.基于Pugh的经验判据,α-Nb_5Si_3和β-Nb_5Si_3的B/G均小于1.75,为脆性,且α-Nb_5Si_3的脆性大于β-Nb_5Si_3,γ-Nb_5Si_3的B/G大于1.75,为韧性.α-Nb_5Si_3、β-Nb_5Si_3和γ-Nb_5Si_3在费米面态密度值依次为14.84 e V、18.89 e V和23.64 e V.因此,α-Nb_5Si_3结构最稳定,γ-Nb_5Si_3结构最不稳定,这与形成能的计算结果一致.α-Nb_5Si_3,β-Nb_5Si_3和γ-Nb_5Si_3费米能级附近价带主要是由Nb的4d轨道及Si的3s和3p轨道贡献,且α-Nb_5Si_3的赝能隙处在高能区,因此结构最稳定.展开更多
文摘The Nb 10Si (mole fraction, %) alloy was fabricated using the vacuum arc melting method and heat treated at 1850?℃ and 1?550?℃ for 2～100?h in Ar atmosphere. The microstructure of the alloy has been investigated using X ray diffractometry(XRD), scanning electron microscopy (SEM) equipped with X ray energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM). The results show that 1?550?℃, 100?h is an optimum heat treatment condition to acquire the equilibrium Nb+Nb 5Si 3 two phase microstructure. The microstructure of Nb 10Si alloy in the as cast condition consists of continuous Nb 3Si matrix and dispersed Nb particles, which implies that the alloy is in the metastable equilibrium state. In the case of 1?850?℃, 2?h heat treatment the Nb particles are coarsened evidently. However, in the heat treatment condition of 1?550?℃ for 25～100?h the growth of Nb particles is unconspicuous. After heat treated at 1?550?℃, Nb 3Si phase transforms into the equilibrium Nb 5Si 3 and Nb phase with the increase of heat treatment time gradually. TEM observations reveal that the interface of Nb phase and Nb 5Si 3 phase is clean and some twins with about 10?nm in width are found.
基金Funded by National Natural Science Foundation of China(No.51271091)Science Project of Jiangxi Ministry of Education of China(No.GJJ12420)
文摘Dense Nb/Nb5Si3 composites were fabricated via spark plasma sintering technology using Nb, Si, and Al elemental powders as raw materials. The microstructttres of the synthesised composites were analyzed through scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. The results show that the composites consisted of residual Nb particle phase and Nb5Si3 phase. The microstructure of the Nb/ Nb5Si3 in situ composites was evidently affected by Al addition, which prompted the formation of the Al3Nb10Si3 phase. In addition, the Rockwell hardness of the composites decreased with the increase in AI additions. The Rockwell hardness of Nb-20Si is 60HRC, which decreased to approximately 52.7 HRC when the Al content increased to 15 at%. The oxidation resistance of the Nb/NbsSi3 in situ composites significantly improved with the increase in Al addition.
文摘基于第一性原理的密度泛函理论(DFT)赝势平面波方法,采用局域密度近似,计算了α-Nb_5Si_3,β-Nb_5Si_3和γ-Nb_5Si_3的电子结构、态密度以及布居数和力学性质.研究表明:三种不同结构的Nb_5Si_3形成能均为负值,均为热力学稳定的,其中α-Nb_5Si_3最稳定.α-Nb_5Si_3、β-Nb_5Si_3和γ-Nb_5Si_3的体积模量分别为:192.3 GPa、188.6 GPa和185.9 GPa;剪切模量分别为130.9 GPa、111.4GPa和24.4 GPa.其中α-Nb_5Si_3具有最高的体积模量和剪切模量.基于Pugh的经验判据,α-Nb_5Si_3和β-Nb_5Si_3的B/G均小于1.75,为脆性,且α-Nb_5Si_3的脆性大于β-Nb_5Si_3,γ-Nb_5Si_3的B/G大于1.75,为韧性.α-Nb_5Si_3、β-Nb_5Si_3和γ-Nb_5Si_3在费米面态密度值依次为14.84 e V、18.89 e V和23.64 e V.因此,α-Nb_5Si_3结构最稳定,γ-Nb_5Si_3结构最不稳定,这与形成能的计算结果一致.α-Nb_5Si_3,β-Nb_5Si_3和γ-Nb_5Si_3费米能级附近价带主要是由Nb的4d轨道及Si的3s和3p轨道贡献,且α-Nb_5Si_3的赝能隙处在高能区,因此结构最稳定.
