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--> --> -->固溶体合金是指在溶剂原子中溶入一定量溶质原子后仍保持溶剂结构特征的合金. 描述固溶体合金就是确定溶质在溶剂中的分布特征, 也就是由于原子间相互的化学作用, 在近程序局域范围, 原子呈现出某种程度的有序行为, 称为化学近程序结构.
人们发展了多种描述固溶体化学近程序的方法, 包括Bragg和Williams[17,18]的长程有序参数、Bethe[19]改进的短程有序参数以及Cowly[20-22]提出的短程序参量数, 但这些参数都是从统计角度出发, 没有建立结构模型, 更无法解释合金成分规律. 在前期工作中, 我们提出了一种描述近程有序结构的方法, 即团簇加连接原子结构模型, 并且该模型已成功应用在准晶[23,24]、金属玻璃[25-28]和一些固溶体合金[29-33]中. 团簇加连接原子结构模型认为[34]: 任何一个合金相的近程序结构都可以看作是由团簇加上位于团簇间隙中的连接原子组成, 用团簇成分式可以表示为[团簇](连接原子), 其中的团簇特指以中心原子为中心的第一近邻配位多面体, 而连接原子则位于次近邻位置.
化学近程序只强烈地发生在最近邻和次近邻位置, 以Ni-Cr-Al基高温合金体系为例[34,35], 其基体为面心立方固溶体
析出相
Ni基高温合金成分式由两种成分式的等比例混合得到, 即50% ×
3.1.$\gamma $ 相的理想团簇成分式
在Co-Al-W三元体系中, 对于图 1 Co-Al基的面心立方固溶体及AuCu3有序结构中的立方八面体[Al-Co12]团簇
Figure1. Cuboctahedron [Al-Co12] cluster in Co-Al-base faced centered cubic solid solution and in AuCu3-type ordered structure
按照文献[34]所提供的方法, 将Co-Al-W合金中
合金成分/at.% | $\gamma $相成分/at.% | 晶格常数实验值/nm | 晶格常数计算值/nm | 绝对误差$\varDelta $ |
Co82Al9W9 | Co81.7Al9.3W9 | 0.3580 | 0.3579 | 0.0001 |
Co83Al9W8 | Co81.9Al10.0W8.1 | 0.3576 | 0.3575 | 0.0001 |
Co80Al9W11 | Co80.7Al9.2W10.2 | 0.3586 | 0.3588 | 0.0002 |
Co74Al9W9Cr8 | Co73.9Al8.0W6.8Cr11.2 | 0.3578 | 0.3575 | 0.0003 |
Co64Al9W9Ni18 | Co69.1Al6.8W7.0Ni16.9 | 0.3577 | 0.3562 | 0.0015 |
Co65Al9W9Ni9Cr8 | Co66.7Al7.8W6.7Ni8.3Cr10.7 | 0.3581 | 0.3584 | 0.0003 |
Co56Al9W9Ni18Cr8 | Co59.2Al6.0W7.4Ni15.6Cr11.8 | 0.3583 | 0.3581 | 0.0002 |
Co72.5Ni10Al10W7.5 | Co76.2Al8.7W5.4Ni9.7 | 0.3578 | 0.3562 | 0.0016 |
表1实测的
Table1.Measured compositions and lattice constants of
将Co, Al, W原子半径代入(6)式, 得x, y和z之间的关系为
2
3.2.$\gamma′ $ 相的理想团簇成分式
在Co-Al-W三元体系中, 首先判断合金元素的原子半径固溶到Co3(Al,W)中是否会发生变化. 根据文献[43]中的数据可知, Co3(Al,W)与Ni3Al相的晶格常数分别为0.3565 nm 和0.3568 nm, 这说明原子半径较大的W原子加入后对
合金成分/at.% | $\gamma′ $相成分/at.% | 晶格常数实验值/nm | W原子半径/nm |
Co82Al9W9 | Co77.49Al10.03W12.48 | 0.3594 | 0.1317 |
Co83Al9W8 | Co76.6Al9.4W14 | 0.3589 | 0.1306 |
Co80Al9W11 | Co75.1Al9.1W15.8 | 0.3595 | 0.1311 |
Co74Al9W9Cr8 | Co73.9Al9.4W10.4Cr6.3 | 0.3587 | 0.1314 |
Co64Al9W9Ni18 | Co58.9Al10.8W11.0Ni19.3 | 0.3590 | 0.1317 |
Co65Al9W9Ni9Cr8 | Co64.2Al10.1W9.9Ni9.4Cr6.4 | 0.3587 | 0.1317 |
Co56Al9W9Ni18Cr8 | Co54.5Al10.5W9.7Ni19.7Cr5.6 | 0.3587 | 0.1319 |
Co72.5Ni10Al10W7.5 | Co68.8Al10.8W9.9Ni10.5 | 0.3593 | 0.1324 |
表2实测
Table2.Atomic radii of W fitted from measured compositions and lattice constants
根据表2所列结果的平均值, 假设在
综上所述, 对于Co-Al-W三元合金, 其
根据现有的Co-Al-W基高温合金成分, 向Co-Al-W三元基体中添加的合金化元素有Ta, Ti, Nb, V, Cr等, 本文根据合金化组元与基体组元Co之间的混合焓
元素 分类 | 合金化 元素 | 混合焓 $\Delta H$/kJ·mol | 元素配分 系数K |
${\overline {{\rm{Co}}} ^{\gamma }}$ | Cr | –4 | 0.48—0.60 |
Fe | –1 | ||
Re | 2 | ||
${\overline {{\rm{Co}}} ^{\gamma′ }}$ | Ni | –2 | 1.08—1.27 |
Ru | –1 | ||
Ir | –3 | ||
Al | Al | –19 | 0.93—1.60 |
${\overline {\rm{W}} }$ | W | –1 | 1.03—6.21 |
Mo | –5 | ||
${\overline {{\rm{Ta}}} }$ | V | –14 | 1.57—8.67 |
Ta | –24 | ||
Nb | –25 | ||
Ti | –28 | ||
Sc | –30 | ||
Hf | –35 |
表3合金化组元与基体组元Co之间的混合焓
Table3.Heats of mixing
合金元素首先分为两大类: 一类是溶剂元素, 称为类Co元素, 用符号
其中, 根据合金元素的配分行为, 溶剂元素
综上所述, 合金化元素可以分为类Co的溶剂元素
1) 溶剂元素
2) Al: 主要溶质元素, 与Co之间呈较强烈的负混合焓, 其含量一般足以占据CN12团簇的中心位置, 是形成团簇的主要元素, 构成
3) 类W元素
4) 类Ta元素
由此, 多元Co-Al-W基合金均可表述为
特别地, Ni3Al可以稳定存在, 但是在Co-Al相图中无稳定的Co3Al存在, 因此需要W, Mo元素辅助Al来稳定
下节利用推出的团簇模型和元素分类, 分析现有典型Co-Al-W基高温合金的成分规律.
5.1.合金成分解析原则及步骤
综上所述, 根据面心立方固溶体的团簇加连接原子结构模型可知, Co-Al-W三元合金以及由此可以确定利用团簇加连接原子结构模型解析Co-Al-W基高温合金成分的步骤为: 1)首先将原子百分比换算成在团簇式所占个数, 即将原子百分比成分乘以0.16 ( = 16/100), 获得以Z = 16团簇式为基础的成分式; 2)将元素归类后放置在团簇成分通式中相应位置, 即得到该合金的团簇成分式.
以Co81.3Al9.2W9.5合金为例, 此时已经表述为原子百分比, 每个成分乘上0.16, 得到在16原子团簇式中分别有13.01个Co、1.47个Al以及1.52个W. 根据团簇模型, 1个Al原子占据团簇中心位置, 12个Co原子占据团簇壳层位置, 其余原子均占据团簇与团簇之间的连接原子位置, 即得到该合金的团簇成分式为: [Al-Co12]Co1.0Al0.5W1.5.
结合Co-Al-W合金的团簇成分通式[Al-Co12](Co,Al,W)3与表3中的合金元素分类, 对现有的Co-Al-W基多元合金的成分进行筛选, 通过解析得到对应的团簇成分式, 如表4所列. 同时统计了符合条件的合金两相成分并进行解析, 结果列于表5中, 筛选条件为: 1)合金中Co元素含量大于等于50 at.%; 2)合金的微观组织中
合金成分/at.% | 团簇成分式-[团簇](连接原子)3 | 连接原子 |
Co78Al10W10Ta2 | [Al-Co12]Co0.5Al0.6W1.6Ta0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.5}{\rm{A}}{{\rm{l}}_{0.6}}{\overline {\rm{W}} _{1.6}}{\overline {{\rm{Ta}}} _{0.3}}$ |
Co78Al9W10Mo3 | [Al-Co12]Co0.5Al0.4W1.6Mo0.5 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.5}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{2.1}}$ |
Co79Al9W10Ti2 | [Al-Co12]Co0.6Al0.4W1.6Ti0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.6}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.6}}{\overline {{\rm{Ta}}} _{0.3}}$ |
Co79Al9W10V2 | [Al-Co12]Co0.6Al0.4W1.6V0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.6}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.6}}{\overline {{\rm{Ta}}} _{0.3}}$ |
Co79Al9W10Si2 | [Al-Co12]Co0.6Al0.4W1.6Si0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.6}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.6}}{\overline {{\rm{Ta}}} _{0.3}}$ |
Co79Al9W8Ta2Nb2 | [Al-Co12]Co0.6Al0.4W1.3Ta0.3Nb0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.6}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.3}}{\overline {{\rm{Ta}}} _{0.6}}$ |
Co79Al9W8Ta2V2 | [Al-Co12]Co0.6Al0.4W1.3Ta0.3V0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.6}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.3}}{\overline {{\rm{Ta}}} _{0.6}}$ |
Co79Al8W9Ta2Ti2 | [Al-Co12]Co0.6Al0.3W1.4Ta0.3Ti0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.6}{\rm{A}}{{\rm{l}}_{0.3}}{\overline {\rm{W}} _{1.4}}{\overline {{\rm{Ta}}} _{0.6}}$ |
Co79.5Al9.7W10.8 | [Al-Co12]Co0.7Al0.6W1.7 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.7}{\rm{A}}{{\rm{l}}_{0.6}}{\overline {\rm{W}} _{1.7}}$ |
Co79.9Al9.4W10.7 | [Al-Co12]Co0.8Al0.5W1.7 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.8}{\rm{A}}{{\rm{l}}_{0.5}}{\overline {\rm{W}} _{1.7}}$ |
Co80Al9W11 | [Al-Co12]Co0.8Al0.4W1.8 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.8}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.8}}$ |
Co80Al9W9Ti2 | [Al-Co12]Co0.8Al0.4W1.4Ti0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.8}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}{\overline {{\rm{Ta}}} _{0.3}}$ |
Co80Al9W9V2B0.04 | [Al-Co12]Co0.8Al0.4W1.4V0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.8}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}{\overline {{\rm{Ta}}} _{0.3}}$ |
Co80Al9W9Ta2 | [Al-Co12]Co0.8Al0.4W1.4Ta0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.8}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}{\overline {{\rm{Ta}}} _{0.3}}$ |
Co80.3Al9.3W10.4 | [Al-Co12]Co0.8Al0.5W1.7 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.8}{\rm{A}}{{\rm{l}}_{0.5}}{\overline {\rm{W}} _{1.7}}$ |
Co80.5Al9W10Si0.5 | [Al-Co12]Co0.9Al0.4W1.6Si0.1 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.9}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.6}}{\overline {{\rm{Ta}}} _{0.1}}$ |
Co81Al9W9Mo1B0.04 | [Al-Co12]Co1.0Al0.4W1.4Mo0.2 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.0}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.6}}$ |
Co81Al9W8Ta2 | [Al-Co12]Co1.0Al0.4W1.3Ta0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.0}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.3}}{\overline {{\rm{Ta}}} _{0.3}}$ |
Co81.3Al9.2W9.5 | [Al-Co12]Co1.0Al0.5W1.5 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.0}{\rm{A}}{{\rm{l}}_{0.5}}{\overline {\rm{W}} _{1.5}}$ |
Co81.5Al9W9Nb0.5 | [Al-Co12]Co1.0Al0.4W1.4Nb0.1 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.0}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}{\overline {{\rm{Ta}}} _{0.1}}$ |
Co81.5Al9W5.5Ta2Mo2 | [Al-Co12]Co1.0Al0.4W0.9Ta0.3Mo0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.0}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.2}}{\overline {{\rm{Ta}}} _{0.3}}$ |
Co82Al9W9 | [Al-Co12]Co1.1Al0.4W1.4 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.1}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}$ |
Co72Al9W9Ni10 | [Al-Co11.7Ni0.3]Ni1.1Al0.4W1.4 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.1}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}$ |
Co82Al9W7.5Mo1.5 | [Al-Co12]Co1.1Al0.4W1.4 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.1}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}$ |
Co80Al9W9Cr2B0.04 | [Al-Co12]Co0.8Cr0.3Al0.4W1.4 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.8}{\overline {{\rm{Co}}} ^\gamma }_{0.3}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.6}}$ |
Co78Al9W9Cr4 | [Al-Co12]Co0.6Cr0.6Al0.4W1.4 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.6}{\overline {{\rm{Co}}} ^\gamma }_{0.6}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}$ |
Co73Al9W9Ni9 | [Al-Co11.7Ni0.3]Ni1.1Al0.4W1.4 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.1}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}$ |
Co64Al9W9Ni18 | [Al-Co10.2Ni1.8]Ni1.1Al0.4W1.4 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.1}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}$ |
Co81.8Al9.2W9 | [Al-Co12]Co1.1Al0.5W1.4 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.1}{\rm{A}}{{\rm{l}}_{0.5}}{\overline {\rm{W}} _{1.4}}$ |
Co72.5Al10W7.5Ni10 | [Al-Co11.6Ni0.4]Ni1.2Al0.4W1.4 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.2}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.4}}$ |
Co81.5Al9W5.5Ta2Ir2 | [Al-Co2]Co1.0Al0.4W0.9Ta0.3Ir0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{1.3}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{0.9}}{\overline {{\rm{Ta}}} _{0.3}}$ |
Co79Al9W8Ta2Cr2 | [Al-Co12]Co0.6Cr0.3Al0.4W1.3Ta0.3 | ${\overline {{\rm{Co}}} ^{\gamma′ }}_{0.6}{\overline {{\rm{Co}}} ^\gamma }_{0.3}{\rm{A}}{{\rm{l}}_{0.4}}{\overline {\rm{W}} _{1.3}}{\overline {{\rm{Ta}}} _{0.3}}$ |
表4Co-Al-W基多元合金的团簇成分式, 所列成分源自文献[2-4, 6, 8, 10, 39, 40-42, 44, 45, 48, 51, 57-62]
Table4.Compositions formulas of Co-Al-W-base multi-element superalloys. The alloy compositions are taken from references [2-4, 6, 8, 10, 39, 40-42, 44, 45, 48, 51, 57-62]
合金成分/at.% | $\gamma $相团簇成分式 | $\gamma′ $相团簇成分式 |
Co82Al9W9 | [Al-Co12]Co1.6Al0.4W1.0 | [Al-Co12]Co0.3Al0.5W2.2 |
Co78Al9W9Cr4 | [Al-Co12]Co0.9Al0.3W0.9Cr0.9 | [Al-Co12]Co0.2Al0.5W1.8Cr0.5 |
Co73Al9W9Ni18 | [Al-Co11.1Ni0.9]Al0.1W1.1Ni1.8 | [Al-Co9.4Ni2.6]Al0.7W1.8Ni0.5 |
Co79.5Al9.7W10.8 | [Al-Co12]Co1.7Al0.4W0..9 | [Al-Co12]Co0.4Al0.6W2.0 |
Co80Al9W9Ti2 | [Al-Co12]Co1.6Al0.4W0.8Ti0.2 | [Al-Co12]Co0.2Al0.4W1.9Ti0.4 |
Co80Al9W9Ta2 | [Al-Co12]Co1.8Al0.4W0.7Ta0.1 | [Al-Co12]Co0.2Al0.4W1.9Ta0.5 |
Co79Al8W9Ta2Ti2 | [Al-Co12]Co2.0Al0.3W0.5Ta0.04Ti0.1 | [Al-Co12]Co0.1Al0.4W1.9Ta0.3Ti0.3 |
Co78Al10W10Ta2 | [Al-Co12]Co1.6Al0.7W0.7Ta0.1 | [Al-Co12]Al0.7W1.9Ta0.4 |
Co78Al9W10Mo3 | [Al-Co12]Co1.7Al0.1W0.8Mo0.4 | [Al-Co12]Co0.2Al0.6W1.7Mo0.5 |
表5部分Co-Al-W基高温合金中
Table5.Composition formulas of
对于表4中所有合金, 将
图 2 合金数量随Co含量的变化, 虚线表示平均成分式
Figure2. Statistical distribution of alloy compositions as a function of at.% Co. The dashed vertical line represents the ideal composition formula
将表4中Co-Al-W基合金成分制作出
图 3
Figure3.
2
5.2.$\gamma /\gamma′ $ 两相成分解析
类似地, 分别绘制合金与两相的数量随Co含量的变化图以及图 4 合金数量随类Co元素总量
Figure4. Evolution of numbers of alloys with
由图4可知,
此外, 根据(8)和(10)式, 当团簇式中连接原子中Al的个数为0.5时, 对于