本文選題：鎂合金　切入點：第一原理計算　出處：《吉林大學(xué)》2015年博士論文

【摘要】：鎂合金具有密度小、比強度和比剛度高等顯著優(yōu)勢，然而室溫下的滑移系統(tǒng)少（僅有兩個獨立滑移系），導(dǎo)致其塑性變形能力很差。傳統(tǒng)鎂合金無法滿足不同環(huán)境和工況對使役性能的需求，嚴重制約了其發(fā)展和在工程上的應(yīng)用。因此，新型高強韌鎂合金的研發(fā)和制備已成為國內(nèi)外學(xué)者的研究熱點。 合金化可促進非基面滑移和孿生等額外變形方式啟動，是改善鎂基體強度和塑性的有效手段；然而當(dāng)前有關(guān)合金元素對鎂基體性質(zhì)的影響規(guī)律和作用機制的系統(tǒng)研究尚不完備。迫于合金設(shè)計的需要，亟需建立鎂合金“數(shù)據(jù)庫”，以優(yōu)化出更多具有潛力的合金元素。廣義層錯能和孿晶界偏析能作為鎂合金“數(shù)據(jù)庫”的兩個重要物理參數(shù)，對預(yù)測合金的力學(xué)性能具有重要意義。具體來說，層錯能降低表明位錯和孿晶形核的可能性增加，有助于啟動額外變形方式；孿晶界偏析能降低代表溶質(zhì)原子偏析的可能性增大，即對孿晶性質(zhì)的改善效果增強。 本論文基于第一性原理計算，研究了合金元素的種類和含量對鎂合金廣義層錯能和孿晶界偏析能的影響規(guī)律和作用機制，為新型高強韌鎂合金的成分設(shè)計提供借鑒和依據(jù)，主要結(jié)論如下： (1)研究了21種合金元素摻雜下鎂合金廣義層錯能的變化規(guī)律�；诨婧头腔婊葡到y(tǒng)對塑性變形的貢獻，提出了廣義層錯能權(quán)重模型，有助于衡量鎂合金的整體變形能力；揭示出隨合金元素與Mg原子半徑差異增大，層錯能降低的共性規(guī)律；在原子半徑相近情況下，元素電負性越大，層錯能越低；與電負性相比，原子半徑對層錯能的影響更大；該結(jié)果為新型高性能鎂合金的成分設(shè)計提供了借鑒。 (2)構(gòu)建了廣義層錯能分布圖，為預(yù)測合金元素對鎂合金塑性的影響提供了依據(jù)。揭示出In、Li、Sn和Bi元素使層錯能下降且在Mg中固溶度大，有助于提高鎂合金的塑性；Cd、Al、Ag、Ga、Zn和Pb元素摻雜可使層錯能較大程度降低，但同時引發(fā)晶格畸變，因而相應(yīng)鎂合金的塑性依賴于摻雜含量；Be、Si、Ge、Cu、Na、Sr和K元素雖然使層錯能大幅下降，然而在Mg中固溶度很小，導(dǎo)致對塑性的改善有限；此外，Al、Sn共摻下I2和T2層錯能降低，即形成不全位錯和孿晶的可能性增加，有助于改善鎂合金塑性；揭示出新型HCP結(jié)構(gòu)Au的基面層錯能比純Mg的低，導(dǎo)致其易于向FCC結(jié)構(gòu)相轉(zhuǎn)變。 (3)選取典型的Al和Zn元素，研究了元素含量對鎂合金廣義層錯能的影響規(guī)律。發(fā)現(xiàn)隨Al或Zn含量升高，基面和非基面滑移系統(tǒng)的廣義層錯能逐漸降低，同時更多滑移位置的不穩(wěn)定層錯能降低，即滑移機會增加；揭示了形成基面和非基面層錯的概率隨Al或Zn含量升高而增加，，有助于改善鎂合金的塑性；同時，體系晶格畸變嚴重，阻礙了位錯的擴展，引發(fā)固溶強化效果；預(yù)測出在理論上應(yīng)存在一臨界含量值，在高于該值時表現(xiàn)“強化”效應(yīng)，反之為“軟化”效應(yīng)。 (4)揭示了Al、Zn對鎂合金廣義層錯能的作用機制，為預(yù)測Mg Al Zn合金中最可能形成層錯位置提供了依據(jù)。Al或Zn元素摻雜下電荷流動性增加，導(dǎo)致滑移面上的Mg Mg鍵變?nèi)�，從而使廣義層錯能降低；揭示出基面a和錐面c+a滑移在含合金元素的原子層以及鄰近摻雜層的Mg層之間均有機會啟動，錐面a層錯易形成于摻雜原子層之間，而柱面a層錯易形成于Mg層之間；為預(yù)測多元鎂合金的塑性變形能力提供了依據(jù)。 (5)研究了19種合金元素摻雜下鎂合金孿晶界偏析能的變化規(guī)律。發(fā)現(xiàn)原子半徑比Pb小的合金元素（包括Pb，特例：{1011}孿晶中Ti和Zr元素）傾向占據(jù){1012}和{1011}孿晶界的壓縮位置；然而比Pb大的合金元素在擴張位置偏析的可能性更大；揭示出孿晶界處化學(xué)鍵越強，應(yīng)變緩解程度越大，溶質(zhì)原子的偏析能力越大；發(fā)現(xiàn)隨合金元素與Mg尺寸（原子半徑、平衡體積）差異增大，孿晶界偏析能降低的共性規(guī)律，同時，偏析能對合金元素尺寸的依賴性比對電負性更大；此外，{1012}孿晶界偏析能與平衡體積（除Ti、Zr和Cd元素），{1011}孿晶界偏析能與原子半徑（除Ag、Zr、Bi和Be元素）之間大致呈直線關(guān)系；該結(jié)果為調(diào)控鎂孿晶性質(zhì)提供了借鑒。 (6)構(gòu)建了孿晶界偏析能分布圖，為預(yù)測合金元素摻雜下鎂合金孿晶強化能力提供了依據(jù)。揭示出Ga、Zn、Al、Ag、Cd、Bi和Ca元素在Mg中偏析能較小、固溶度適中，可用于提高鎂孿晶強化能力；Be、Si、Ge、Sb、Na和Sr元素雖然使偏析能大幅下降，然而固溶度很小，導(dǎo)致孿晶強化效果有限；揭示出Zn（壓縮位置）和Ca元素（擴張位置）共同摻雜可使偏析能更大程度下降，有助于穩(wěn)定孿晶結(jié)構(gòu)；發(fā)現(xiàn)隨Zn含量增加，孿晶界偏析能逐漸下降，彈性應(yīng)變量減小，導(dǎo)致偏析可能性增大；有助于篩選多元合金元素調(diào)控鎂孿晶性質(zhì)。 總之，本文研究了合金元素對鎂合金廣義層錯能和孿晶界偏析能的影響規(guī)律，構(gòu)建了層錯能和偏析能分布圖，為預(yù)測合金元素摻雜下鎂合金的塑性變形和孿晶偏析能力提供了依據(jù)；基于電子結(jié)構(gòu)或應(yīng)變場，揭示了合金元素對層錯能和偏析能的作用機制，有助于更好地調(diào)控合金元素；對建立鎂合金“數(shù)據(jù)庫”，推動新型高性能鎂合金研發(fā)和制備具有積極意義。
[Abstract]:The magnesium alloy has the advantages of small density , higher specific strength and higher specific rigidity , but less slip system at room temperature ( only two independent slip systems ) , which leads to poor plastic deformation capacity . Traditional magnesium alloys can not meet the requirements of different environments and working conditions on the performance of the service , severely restrict its development and application in engineering . Therefore , the research and development of the new high - toughness magnesium alloy has become a hot spot for scholars at home and abroad .

It is an effective means to improve the strength and plasticity of magnesium matrix , which can promote the initiation of non - base slip and twin deformation .
However , the research on the effects of alloying elements on the properties of magnesium matrix is not complete . For the sake of alloy design , it is urgent to establish the magnesium alloy " database " to optimize the alloy elements with potential . The generalized layer fault energy and the twin segregation energy can be used as two important physical parameters of the magnesium alloy " database " , which is of great significance to predict the mechanical properties of the alloy .
Twin - grain segregation reduces the possibility of segregation of solute atoms , that is , the improvement of the twin properties is enhanced .

Based on the calculation of the first principle , the influence law and mechanism of the kinds and contents of the alloy elements on the generalized layer fault energy and the twin segregation energy of the magnesium alloy are studied , and reference and basis for the composition design of the new high toughness magnesium alloy are provided . The main conclusions are as follows :

( 1 ) The change law of the generalized layer fault energy of the magnesium alloy under the doping of 21 kinds of alloy elements is studied . Based on the contribution of the base surface and the non - base slip system to the plastic deformation , a generalized layer fault energy weight model is proposed , which can help to measure the overall deformation ability of the magnesium alloy ;
The commonness law of the reduction of the layer ' s fault energy is revealed with the increase of the difference between the alloy element and the Mg atom radius .
When the atomic radius is similar , the greater the electronegative of the element , the lower the fault energy of the layer ;
The effect of atomic radius on the layer ' s fault energy is bigger than that of electronegative .
The results provide a reference for the composition design of the new high - performance magnesium alloy .

( 2 ) In order to predict the effect of alloy elements on the plasticity of magnesium alloy , the distribution diagram of generalized layer error energy is constructed . In addition , In - , Li , Sn and Bi elements can decrease the layer ' s fault energy and the solid solubility in Mg is large , which can help to improve the plasticity of magnesium alloy ;
The doping of Cd , Al , Ag , Ga , Zn and Pb can greatly reduce the layer error , but also induce lattice distortion , so the plasticity of the corresponding magnesium alloy depends on the doping content .
Be , Si , Ge , Cu , Na , Sr and K elements decrease the layer ' s fault greatly , however , the solid solubility in Mg is very small , which leads to the improvement of plasticity .
In addition , Al and Sn co - doped with I2 and T2 layers can be reduced , that is , the possibility of forming dislocation and twin is increased , which is helpful to improve the plasticity of magnesium alloy ;
It is revealed that the base layer fault energy of the novel HCP structure Au is lower than that of pure Mg , which leads to its easy transition to the FCC structure .

( 3 ) A typical Al and Zn element is selected to study the effect of element content on the generalized layer fault energy of magnesium alloy . It is found that the generalized layer fault energy of the base and non - base slip system decreases gradually with the increase of Al or Zn content , and the dislocation energy of unstable layer at the same time is decreased , that is , the slip opportunity increases ;
The probability of forming base surface and non - base layer is increased with the increase of Al or Zn content , which helps to improve the plasticity of magnesium alloy ;
At the same time , the lattice distortion of the system is serious , the dislocation expansion is hindered , and the solid solution strengthening effect is initiated ;
It is predicted that there should be a critical content value in theory , which exhibits a " hardening " effect when higher than the value , and vice versa .

(4)鎻ず浜咥l,Zn瀵歸晛鍚堥噾騫夸箟灞傞敊鑳界殑浣滅敤鏈哄埗,涓洪嫻婱g Al Zn鍚堥噾涓渶鍙兘褰㈡垚灞傞敊浣嶇疆鎻愪緵浜嗕緷鎹

本文編號：1709054