【作者】 陈敏；

【导师】 王崇愚；

【作者基本信息】 清华大学 ， 物理学， 2010， 博士

【摘要】 基于第一原理密度泛函理论,对钴基高温合金,我们研究了一系列元素在γ-Co₃（Al,W）相中的择优占位,以及Re和Ru在两相中的分配行为。本文研究合金化元素包括Mo,Ta,铂族元素（Ru,Rh,Pd,Os,Ir和Pt）以及3d元素（Ni,Fe,Mn,Cr,V和Ti）在Co₃（Al,W）中的择优占位。L12结构的Co₃（Al,W）中Co原子择优面心,Al和W原子则在顶角,但没有实验报道顶角上Al和W原子的有序排列。首先,我们需要建立一个合理的L12结构Co₃（Al,W）模型,进而实行一系列元素在Co₃（Al,W）中的择优占位计算。计算结果表明,Mo,Ta和铂族元素（PGMs）中,Mo,Ta,Rh,Ir和Pt,可使γ-Co₃（Al,W）相变稳定。在γ-Co₃（Al,W）中添加的PGMs有三种基本的择优占位:Mo和Ta有很弱的择优占W位倾向;Ru和Os有很弱的择优占Co位倾向;而其他的PGMs原子如Rh、Pd、Ir和Pt倾向于占Co位,且它们择优占Co位的倾向依次是:Ir<Rh<Pt<Pd。另外,合金化元素择优占位确定后,由于PGMs原子的添加引起的晶格常数增长次序为:Mo<Ta<Rh<Ru<Os<Ir<Pd<Pt。计算还显示,3d元素中,Ni,Fe,V和Ti可使γ-Co₃（Al,W）相变稳定。在γ-Co₃（Al,W）中添加3d元素的择优占位,计算指出:Ni,Fe和Mn倾向于占Co位;Cr,V和Ti倾向于占Co或W位。此外,我们的计算还发现当确定择优占位后,由3d原子所引起的晶格常数增长次序为:Fe<Ni<Mn<Cr<V<Ti。本文还研究了Re和Ru在γ/γ两相中的分配行为,以及Ru对Re的分配行为的影响。计算模型是含有192个原子的γ/γ界面模型。计算结果表明,Re和Ru都倾向于γ相分配,Ru的加入会抑制Re往γ相分配的行为。同时我们还计算了Re和Ru在γ-Co₃（Al,W）中的择优占位,Re倾向于占W位,Ru倾向于占Co位。电子结构的分析表明,在有Re的基础上添加Ru后,Ru主要通过Re-Ru-W之间较强的化学成键影响Re的分配行为。更多还原

【Abstract】 The site preference of alloying elements inγ-Co₃（Al, W）, and the partitioning be-haviors of Re and Ru betweenγandγphases in Co-based superalloys are investigatedby ab initio calculations.The site preference of various alloying elements in Co₃（Al, W） are studied usingfirst principle VASP method. The elements include Mo,Ta,platinum group metals（Ru,Rh,Pd,Os,Ir and Pt） and 3d metal elements （Ni,Fe,Mn,Cr,V and Ti）. Theresult we present in current work based on a proper model of 32-atomγ-Co₃（Al, W）supercell, which is confirmed to be valid for the study of site preference of alloyingelements.The calculation results of site preference of alloying elements inγ-Co₃（Al, W）are as follows. For Mo,Ta and platinum group metals （PGMs）, Mo, Ta, Rh, Ir andPt can stabilizeγphase. The addition of those PGMs element modifies the latticeparameter ofγphase and it increases in the order of Mo< Ta < Rh < Ru < Os < Ir <Pd < Pt. We recognize three types of site preferences: Mo and Ta weakly prefer the Wsite, Ru and Os have a weak preference for Co site, while Rh, Pd, Ir and Pt prefer theCo site. For 3d transition metal elements, Ti, V, Fe and Ni are proved to stabilize theγphase. The addition of 3d transition elements modify the lattice constant of theγphase. It increases in the order of Fe<Ni<Mn<Cr<V<Ti. Four types of site preferencesare identified: Ni prefers Co（1）; Fe prefers Co（3）; Mn prefers the face center Co（1,2,3）sites almost equally; Cr, V and Ti have a site preference for the face center Co（1） siteor the cube corner W site equally.The partitioning behaviors of Re and Ru betweenγandγphases in Co-basedsuperalloys are studied by density functional theory using a 192-atom Co-basedγ/γsupercell model. Both Re and Ru are found to partition more strongly to theγphase,but the addition of Ru element depresses the partitioning trend of Re intoγphase. Reand Ru are found preferentially substitute the W and Co（1） sublattice sites in the L12 Co₃（Al, W）, respectively. Moreover, the investigation of the impurity-induced chargedensity characteristics shows that the strong interaction between Re（Ru） and its NNCo atoms inγphase conduce to theγ-phase partitions of Re and Ru, and the stronginteractions between Re-Ru-W inγphase are responsible for the in?uence e?ect ofRu addition on the partitioning behavior of Re.更多还原