Diffusion bonding of refractory Nb–Si-based alloy was performed with Ni/Al and Ti/Al nanolayers under the condition of 1473 K/30 MPa/60 min.The NbSS/Nb5Si3 in situ composite with the nominal composition of Nb–22 Ti...Diffusion bonding of refractory Nb–Si-based alloy was performed with Ni/Al and Ti/Al nanolayers under the condition of 1473 K/30 MPa/60 min.The NbSS/Nb5Si3 in situ composite with the nominal composition of Nb–22 Ti–16 Si–3 Cr–3 Al–2 Hf was used as the parent material.The joint microstructures were examined by using a scanning electron microscope equipped with an X-ray energy dispersive spectrometer.Shear test was conducted for the bonded joints at room temperature.Within the joint bonded with Ni/Al multilayer,element diffusion occurred between the base metal and the nanolayer,with the reaction products of AlNb2+Ni3 Al,NiAl and AlNi2 Ti phases.The average shear strength was 182 MPa.While using Ti/Al multilayer,the interface mainly consisted of TiAl,(Ti,Nb)Al and(Ti,Nb)2 Al phases,and the corresponding joints exhibited an increased strength of 228 MPa.In this case,the fracture mainly took place in the TiAl phase and presented a typical brittle characteristic.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
基金financially supported by the Beijing Municipal Science & Technology Commission (No. Z171100002217048)the National Natural Science Foundation of China (No. 51705489)
文摘Diffusion bonding of refractory Nb–Si-based alloy was performed with Ni/Al and Ti/Al nanolayers under the condition of 1473 K/30 MPa/60 min.The NbSS/Nb5Si3 in situ composite with the nominal composition of Nb–22 Ti–16 Si–3 Cr–3 Al–2 Hf was used as the parent material.The joint microstructures were examined by using a scanning electron microscope equipped with an X-ray energy dispersive spectrometer.Shear test was conducted for the bonded joints at room temperature.Within the joint bonded with Ni/Al multilayer,element diffusion occurred between the base metal and the nanolayer,with the reaction products of AlNb2+Ni3 Al,NiAl and AlNi2 Ti phases.The average shear strength was 182 MPa.While using Ti/Al multilayer,the interface mainly consisted of TiAl,(Ti,Nb)Al and(Ti,Nb)2 Al phases,and the corresponding joints exhibited an increased strength of 228 MPa.In this case,the fracture mainly took place in the TiAl phase and presented a typical brittle characteristic.
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.
