B1型碳化物与bcc铁基体共格界面能的电子理论计算与分析

Theoretical Calculation and Analysis of Coherent Interfacial Energy between B1-Type Carbides and bcc Iron Matrix Based on Valence Electron Structures

运用固体与分子经验电子理论(EET),对Nb、Ti、V3种不同Fe-M-C合金系fcc铁基体(α)、析出的B1型碳化物(ξ)和α/ξ共格界面区(σ)各晶胞价电子结构进行了计算;在此基础上,通过共价键能将EET与离散点阵平面/最近邻断键(DLP/NNBB)模型结合,对以上3种不同合金系的B1型碳化物与bcc铁基体共格界面能进行了理论计算与分析。计算结果表明,合金元素在α/ξ界面区产生偏聚作用,增强了共价键络,产生了固溶强化作用;随着含碳量的增加,C-M偏聚作用增强,界面能逐渐增大;α/ξ共格界面能随温度增加而略有下降,变化范围为1.10～1.45J/m2,与相关文献所得结果一致,Fe-Nb-C合金系α/ξ共格界面能随温度下降最快;Fe-Nb-C合金系α/ξ共格界面能最大,故Nb元素对相变过程晶粒细化效果最好;随着合金元素含量的增加,固溶于铁基体和界面区的含碳量减少,偏聚作用减小,α/ξ共格界面能缓慢下降。

The valence electron structures of unit cells of the bcc iron matrix,B1-type carbides and the bonds across the interface（σ） in Fe-M-C alloy systems（M=Nb,Ti,V） were calculated using the Empirical Electron Theory in Solid and Molecules（EET）.Based on the calculational results,the coherent interfacial energy between B1-type carbides and bcc iron matrix in Fe-M-C alloy system was calculated and analyzed by combining the EET with discrete lattice plane/nearest neighbor broken bond（DLP/NNBB） method through covalence-bond energy.The results show that the solution strengthening is produced because the solute phase boundary segregation happens and the covalence-bond net is enhanced.Because the solute phase boundary segregation is enhanced by the increase of the carbon content,the interfacial energy increases at the same time.The interfacial energy decreases in the range of 1.10 to 1.45 J/m2 with the increase of temperature,according with referred documents.It decreases faster for Fe-Nb-C alloy system.The coherent α/ξ interfacial energy is largest in Fe-Nb-C alloy system,so the grain refining effect of Nb is best for ferrite phase transformation.The carbon content of iron matrix and unit cells across the interface decreases with the increase of alloyed element content,so the solute phase boundary segregation decreases.The coherent α/ξ interfacial energy diminishes slowly.