基于第一性原理的含空位a-Fe和H原子相互作用研究

Investigation of interaction between a-Fe metal and H atom by ab-initio method

氢致裂纹是制约超高强度钢应用的关键问题,掌握扩散氢的分布行为有助于弄清氢致裂纹的形成机理.本文采用第一性原理方法计算了H原子占据α-Fe晶格间隙和空位时的情况,得到了晶体的稳定构型及能量,并据此分析了H原子在晶格间隙和空位中的溶解倾向;从Mulliken布居、电子密度分布、态密度分布等角度分析了H原子与α-Fe晶体间隙和空位之间的相互作用.结果表明:间隙H原子倾向占据α-Fe四面体间隙位,其1s轨道电子与Fe的4s轨道电子呈微弱共轭杂化;空位是强氢陷阱, H原子倾向占据空位内壁附近的等电荷面.在真空0 K条件下单空位最多稳定溶解3个H原子,且H原子之间未表现出自发形成H2的倾向;间隙和空位中的H原子溶入改变了Fe晶格内电子分布导致原子结合力弱化,并在局部区域形成反键.基于第一性原理能量计算结果开展热力学分析,分析结果表明大多数情况下间隙H原子都是H主要的固溶形式, H平衡溶解度计算结果与实际符合良好.

Hydrogen-induced cracking(HIC) is a key problem restricting the application of ultra-high strength steel.It is necessary to analyze the distribution of diffusible hydrogen to reveal the mechanism of HIC. The site occupation tendency of H in interstitial and vacancy positions are investigated by the ab-initio method, and the stable configuration and steady state energy are obtained. The solution tendency of H atom in interstitial and vacancy positions is analyzed based on the aforementioned results. Specifically, the Mulliken population, density of states, charge density difference are calculated and used to analyze the interaction between a-Fe metal and H atom. The results show that the dissolved H tends to occupy the interstitial sites of the body-centered cubic,the weak hybridization interaction between the interstitial hydrogen and its nearest neighbour Fe atom is contributed by the H 1s orbital and Fe 4s orbital. Vacancies can capture H atoms easily and H atoms tend to occupy the isoelectric surface near the inwall of the vacancies. A vacancy defect can hold up to three H atoms which are difficult to combine with each other to form H2 molecule by covalent bond. H atoms in vacancies and at interstitial positions change the charge distribution of the Fe lattice, which weakens the binding force of the atoms and forms anti-bonding orbital in local area. The proposed thermodynamical model allows the determining of the equilibrium vacancy and the dissolved H concentration for a given temperature and H chemical potential in the reservoir, and the calculated results are in good agreement with the actual results.