稀土La对含铌钢中NbC在α-Fe中析出行为的影响

Effect of Lanthanum on NbC Precipitation Behavior in the α-Fe Region of Niobium-Containing Steels

采用基于密度泛函理论(DFT)的第一性原理,研究了稀土La对含铌钢中NbC在铁素体区析出行为的影响。计算了α-Fe中La原子和Nb原子与空位之间,以及La原子和Nb原子之间的点缺陷结合能;此外,讨论了La在α-Fe中与Nb扩散激活能的关系。在此基础上,分析了稀土加入对铌析出行为的影响。结果表明:La原子与空位之间有较强的相互吸引作用,而与Nb原子之间则为相互排斥,这种结合能的差异会造成Nb的扩散迁移能有所升高。同时,La的加入使Nb原子近邻的空位形成能显著降低,从而促进α-Fe中Nb原子近邻空位的形成。迁移能与空位形成能变化的计算结果显示,La能够使α-Fe中Nb的扩散激活能显著降低,从而促进了铁素体区NbC的析出。

The effect of La on the precipitation of NbC in ferrite region of Nb-containing steel has been investigated by the first principles method based on the density functional theory. The binding energies of La-vacancy and Nb-vacancy pairs were calculated, as well as the La-Nb pair, and the effects of La on the diffusion activation energy of Nb in α-Fe were also considered. The result indicates that there exists a strong attractive interaction between La atom and vacancy, but a repulsive interaction between La atom and Nb atom. This difference of binding energy leads to the increasing of the migration energy of Nb. At the mean time, with the addition of La, the vacancy formation energy decreases significantly, thus promoting the formation of vacancy next to Nb atom in α-Fe. The calculated result of the vacancy formation energy and migration energy shows that La decreases the diffusion activation energy of niobium significantly, thus promoting the precipitation of NbC in ferrite region.