P,N影响Fe晶界结合的第一原理研究

First Principle Research on Effect of P, N Impurities on Fe Grain Boundary Cohesion

本文利用第一原理离散变分方法,计算了轻杂质P、N在体心Fe∑3[110](111)晶界和Fe(111)表面的偏聚能,从能量方面对P,N的韧脆机制进行了探讨。结果表明,P在晶界上的偏聚能比表面上更高,更有利于偏聚在表面而非晶界,而N则相反。因此,P为脆性杂质,N为韧性杂质,此结果与实验观察相符。还分析了造成这一结果的化学因素和力学因素的影响。

The segregation effects of P and N on the Fe bcc Fe∑3 [1 1 0] (111) grain boundary cohesion are studied by electronic structure calculation using the discrete variational method within the framework of density functional theory. As a result, P has the higher segregation energy on the grain boundary(GB) than on the surface, thus segregates rather on the GB than on the surface; while N is reverse. Therefore, P is brittle impurity and N is ductile dopant. In addition, the mechanical and chemical factors are analyzed for these effects and the necessity of structure relaxation is emphasized.