晶体结构对316不锈钢腐蚀影响的第一性原理研究

Influence of Crystall Structure on Corrosion Resistance of 316 Stainless Steel by First-Principles Calculation

316不锈钢的耐腐蚀问题是研究者关注的热点之一。基于密度泛函理论第一性原理,运用Materials Studio软件中CASTEP模块,对316不锈钢的晶体(奥氏体、铁素体、渗碳体和Fe合金)进行总能量和电子结构模拟计算,考察晶胞总能量、能带结构及电子态密度对316不锈钢腐蚀性能的影响。晶胞总能量计算结果表明,渗碳体和Fe合金的晶胞总能量最小,其次是奥氏体,最后为铁素体。说明,316不锈钢中渗碳体和Fe合金的性质最稳定、抗腐蚀性能最好,而铁素体的抗腐蚀性最差。随着316不锈钢中Cr含量增加,晶胞总能量逐渐减小,各相态晶体结构的稳定性逐渐变强。说明,当受到腐蚀介质侵蚀时,增加Cr的含量可提高316不锈钢的稳定性和耐腐蚀性。能带图和电子态密度结果表明,渗碳体和Fe合金的能带宽度小而密集且局域性强,而铁素体能带宽度大且非局域性强。说明,渗碳体和Fe合金的性质更稳定、抗腐蚀性能更好,而奥氏体次之,铁素体抗腐蚀性最差。随着316不锈钢中Cr含量增加,含Cr奥氏体的最大峰值对应的能量越低,区域分布的核外电子数越少。核外电子分布较少,不易失去电子,也不易发生氧化还原反应,结构越稳定。在发生腐蚀过程中,含Cr高的奥氏体结构更稳定,耐腐蚀性能更好,这一结论符合贫铬理论或晶间区偏析杂质理论。

The problem of corrosion resistance of 316 stainless steel has always been a hot topic for researchers.The crystal total energy and electronic structure of austenite,ferrite,Fe alloy and cementite in the 316 stainless steel were simulated and computed by the CASTEP module of the Materials Studio software.The influence of crystal total energy,band structure,electronic density of states of crystal phase in the 316 stainless steel on the corrosion resistance has been investigated by the first principles method based on the density functional theory(DFT).The total energy results showed that the most stability of crystal phase in the 316 stainless steel were Fe alloy and cementite,next was austenite,and finally was ferrite.It suggests that the corrosion resistance of Fe alloy and cementite has higher than austenite and ferrite.Additionally,the crystal total energy of Fe-Cr alloy decreased with increasing Cr content.It is implied that adding Cr content can improve the stability and corrosion resistance of stainless steel as 316 stainless steel is being corroded.Besides,the results of band structure and electronic density of states display that the band width of cementite and Fe alloy decreases,and their locality increases.But the band width of ferrite becomes large and its non-locality increases.It indicates that the stability and corrosion resistance of cementite and Fe alloy are higher.With the increase of Cr content,the energy corresponding to the maximum peak of Crcontaining austenite is lower,the number of extranuclear electrons distributed in the region is less,the distribution of extranuclear electrons is less,the electrons are not easy to lose,and the redox reaction is not easy to occur,and the structure is more stable.During the corrosion process,the austenite structure with high Cr content is more stable and the corrosion resistance is better.This conclusion is consistent with poor chromium theory or intercrystallite impurity segregation theory.