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QI Yunxin TANG Wentai XIA Jianguo Nei Mongol Institute of Metallic Materials Baotou ChinaLI Wang ZHAN Zhenzong Institute of Physical Chemical Engineering Research Tianjin China 《金属学报(英文版)》1991,4(9):219-224
The surface segregation of substrate elements through the Au layer in the Au-Ni-Kovar sys- tem specimens heated at 250—350℃ for 0.5—1.5 h has been studied by SAM and XPS. Visual evidence of the mechanism for Ni and Co surface segregation of the complicated sys- tem has been given,i.e.Ni and Co penetrated the gold layer mainly by grain boundary diffu- sion and then covered the Au layer by surface diffusion.The strdy results of the chemical states of surface segregation elements not only indicate that oxygen adsorption and oxidation reaction are the driving force for the surface segregation of Ni and Co,but also show that the above segregation can result in water absorption on surfaces. 相似文献
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采用溶胶-凝胶法制备了La3+掺杂TiO2。利用XRD、TEM、HRTEM、STEM-EDS、XPS和UV-Vis对样品进行表征,讨论La3+掺杂TiO2在相变过程中的物相组成、平均晶粒尺寸、微观结构、化学态和紫外-可见吸收光谱等方面的变化。结果表明,掺杂La3+明显地抑制了TiO2的相转变和晶粒长大,有效地改善了TiO2的分散性,并减小了TiO2的平均颗粒尺寸。随着煅烧温度升高,La3+掺杂TiO2逐渐析出第二相La4Ti19O24,其会与TiO2板钛矿相形成非共格界面,并以不规则球体的形式在TiO2基体表面析出。第二相La4Ti19O24来源于点缺陷在La掺杂TiO2晶界的偏析,偏析驱动力主要是是弹性应变能。随着煅烧温度的升高,La3+掺杂TiO2中O 1s的原子分数逐渐降低,La 3d的原子分数逐渐升高,且La 3d主峰的高结合能端有一个能量损失峰,煅烧后存在Ti3+;掺杂La3+使TiO2的光吸收带边红移,但随着煅烧温度的升高,其光吸收带边蓝移。 相似文献
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业已证实,淬火硼钢中硼向奥氏体晶界的偏聚,是在冷却过程中发生的一种非平衡的晶界偏聚。本文通过解变温扩散方程,导出了非平衡晶界偏聚的理论公式,建立了晶界贫硼区宽度与淬火加热温度、冷却速度以及非平衡晶界偏聚扩散激活能与扩散常数之间的关系,理论预言与实验结果较好地吻合。 根据实验结果和理论分析,提出这种非平衡晶界偏聚的机制,是在冷却过程中,过饱和空位或双空位带着硼原子向晶界(空位阱)迁移的结果。 基于这种非平衡晶界偏聚的新概念,可以较完满地说明影响硼钢淬透性的众多复杂因素。 相似文献
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通过显微组织观察和对临界转变温度的测定,研究了稀土元素La对碳锰纯净钢组织和冷却转变过程的影响。结果表明,当镧含量较高时,纯净钢冷却转变组织粗化,形成魏氏组织的趋势增加,珠光体片层间距不均匀;在碳锰纯净钢的冷却转变过程中,随La含量的增加,先共析铁素体开始析出温度降低,析出速度加快,共析转变开始温度降低。镧在晶界的偏聚是造成碳锰纯净钢组织和相变过程变化的主要原因。 相似文献
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Zheng Ziqiao Zhao Yongqing Liu Minggui Yin Denfeng Deptartment of Materials Science Engineering Central South University of Technology Changsha China 《中国有色金属学会会刊》1993,(4)
The effect of the addition of minor amounts of La on the microstructure and mechanicalproperties of an Al-Li-Cu-Mg-Zr alloy was studied.The results showed that in Al-Li alloyssome impurities,such as Fe,Si and Na segregated on the grain boundaries,and the addition ofminor amounts of La decreased the segregation of these impurities.In addition,La could giverise to grain refinement,and retard the growth of precipitates.The tensile properties andtoughness of the Al-Li alloy containing minor amounts of La were improved compared with theLa-free Al-Li alloy. 相似文献
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《Scripta materialia》2003,48(6):791-796
The experimentally measured grain size compensated diffusion creep rates are essentially identical in cubic, tetragonal and monoclinic zirconia, suggesting a similarity in the absolute magnitudes of their grain boundary diffusion coefficients. However, grain growth is substantially slower in tetragonal zirconia due to significant grain boundary segregation. 相似文献
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J.H. Selverian 《Acta Materialia》1997,45(12):5099-5110
A finite difference model of thorium transport in tungsten electrodes and its effect on the thermionic emission current is presented. Lattice, grain boundary and surface diffusion, grain boundary and surface segregation, evaporation, limited solubility and the rate of formation of thorium metal from thorium oxide are included. From the view of thermionic emission, the “ideal” grain size depends on the operation temperature of the electrode. High operation temperatures (T > 2300 K) favor larger grain sizes. Low operation temperatures (T < 2000 K) favor smaller grain sizes. The emission current is sensitive to the prior thermal treatments that the electrode has seen. 相似文献
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To investigate the mechanisms by which Y and La dopants affect the oxidation behavior of Ni-base single‐crystal superalloys, the oxide scales formed on two variants of a commercial X4 alloy, each with and without a MCrAlYHfSi coating were characterized. The alloy systems were oxidized for 100 h at 1100 °C and then examined using analytical transmission electron microscopy. Without a coating, a duplex scale was formed on the superalloy surface comprised of an outer Ni‐rich spinel‐type layer and an inner columnar α‐Al2O3 layer. In this case, Hf and Ti were found segregated to the alumina grain boundaries in the outer part of the scale on both alloys but only Hf was detected near the metal–alumina interface. There was no evidence of Ta, Y or La segregation to the alumina scale grain boundaries after this exposure. The scale formed on the alloys with the thermally sprayed coating was primarily alumina, and Y and Hf segregated to the alumina grain boundaries for both alloys. There was evidence of Ti-rich oxides in the outer part of the scale indicating that Ti had diffused through the coating into the thermally grown oxide but La was not found. 相似文献
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《Acta Materialia》2001,49(1):1-11
The problem of grain boundary motion in the diffusion field of a solute is formulated for the case of infinitely fast diffusion along a straight boundary. The steady state solution suggests that (de)alloying occurs by two different modes, namely: the solute diffusion through the stationary boundary to the bulk, or by diffusion-induced grain boundary migration (DIGM). The transition from one mode to another depends on the grain boundary segregation coefficient. The result enables an assessment of the relative importance of different possible driving forces. When the equilibrium concentrations of the bulk solute with the external gas is low, the entropy of mixing is the leading driving force. DIGM does not occur in isotope solution because the solute atom does not segregate to the boundary. Based on this theory, we construct the phase diagram in the plane of the (gas/bulk) equilibrium concentration vs the segregation coefficient, representing the transition from DIGM to alloying via stationary boundaries. 相似文献
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The steel of a higher bulk carbon content shows the denser precipitation distribution of carbides after the solution treatment followed by tempering. Such a carbide distribution produces the smaller prior austenite grain size after the welding simulation at a high temperature. Because the equilibrium segregation concentration of phosphorus decreases with decreasing prior austenite grain size, the specimen of the higher bulk carbon content shows therefore the longer intergranular rupture life. The rupture life is also increased by the partitioning of phosphorus pre-segregated at prior austenite grain boundary/carbide interfaces onto the fresh surface of precipitates formed on the surface of pre-formed carbides. The intergranular rupture life is additionally increased by the repulsive segregation between carbon and phosphorus which decreases the overall phosphorus segregation concentration at the prior austenite grain boundaries. 相似文献
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采用NaCl的质量分数为3.5%的溶液对四种Al-Si-Cu钎料的真空钎焊接头进行全浸试验,对腐蚀后的钎焊接头进行观察,分析接头的腐蚀类型,研究接头的腐蚀机理,对Cu的晶界偏析及扩散进行了讨论。结果表明,铝基钎料真空钎焊后的接头仍然存在腐蚀问题,腐蚀产物为A1Cl3、Al(OH)3、Al(OH)2Cl,腐蚀类型有点蚀和晶间腐蚀;并且随着Cu含量的增加腐蚀加重,Cu的偏析与扩散对接头腐蚀行为产生重要的影响,在晶界形成他Cu,使晶界周围形成贫Cu区,与晶粒内部处于钝态的αAl存在较大电位差,构成局部腐蚀电池,形成晶间腐蚀。 相似文献
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采用高分辨透射电子显微镜和高角环形暗场扫描透射电子显微镜结合X射线能谱仪,研究Al-Zn-Mg-Cu合金叩相沿小角晶界的析出序列。试样在135℃分别时效5min到6h。结果表明,η相在小角晶界的析出序列是:SSS→VRC→GPⅡ区→η’→η。基于非平衡晶界偏析和非平衡晶界共偏析理论,在Al-Zn-Mg-Cu合金时效过程中,通过溶质一空位对的扩散,大量的沉淀形成元素偏析到晶界。这种晶界偏析在VRC、GPⅡ区、η’相和η相的形核和生长中起重要作用。 相似文献
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V. V. Popov A. V. Sergeev N. K. Arkhipova A. Yu. Istomina 《The Physics of Metals and Metallography》2011,112(3):256-266
Based on the recently proposed model of grain-boundary diffusion, the available research data on grain-boundary diffusion of Co in W, and on emission Mössbauer studies of grain boundaries in polycrystalline W have been analyzed in detail. Using joint processing of primary data for tracer analysis and Mössbauer studies, all the parameters of grain-boundary diffusion of Co in W have been determined: the coefficient of grain-boundary segregation, coefficient of grain-boundary diffusion, and the diffusion width of the grain boundary. 相似文献
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采用溶胶-喷雾干燥法制备纳米晶(W,Ni,Fe,La)复合粉末,研究了粉末在烧结过程中La对抑制鼓泡和晶粒长大的作用机理,通过XRD与SEM分析了La在烧结过程中的相转变规律和在合金中的存在形式,讨论了稀土La对合金液相烧结过程中扩散的影响。结果表明:稀土La在纳米复合粉末中主要以La2WO6与La4W2O15的形式存在。经液相烧结后,稀土La主要以二次相颗粒的形式分布于粘结相中,生成高温下能稳定存在的La4W2O15相,该相对杂质元素Ca、O具有很好的亲和力,起到晶界净化和晶内净化的作用。同时二次相颗粒存在于粘结相中,抑制了W在粘结相中的扩散,降低了W在粘结相中的溶解度,使得液相烧结溶解-析出过程减慢,从而抑制液相烧结阶段的晶粒长大和鼓泡现象。 相似文献
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HU Benfu University of Science Technology Beijing Beijing ChinaTAKAHASHI Heishichiro ITOH Hisatoshi TAKEYAMA Taro Hokkaido University Sapporo Japan Associate Professor Dept of Materials Science Engineering University of Science Technology Beijing Beijing China 《金属学报(英文版)》1990,3(4):229-235
The behavior of void swelling and segregation in Fe-15Cr-xMn alloys and an alloy con-taining small amount of W and V was investigated by electron-irradiation.The compositionalanalysis in the irradiated regions including grain boundaries was performed.The resultdts showthat there are many common features of irradiuation tehavior in the Fe-Cr-Mn andFe-Cr-Ni systems while there are some significant differences,In the Fe-Cr-Mn alloy sys-tems void swelling was rematrkably suppressed and at the same time the radiation-inducedsegregation was also retarded,furthermore,the segregation was strongly retarded in anFe-15Cr-15Mn alloy containing small amount of W and V.The results also show that Ni re-placed by Mn does not in general confer immunity from either swelling or phase instabilities.The phase instability is due to the different diffusion behavior of Ni and Mn in reponse to theoperation of the inverse-Kirkendall effecr.Fe segregates to the microstructural sinks in theFe-Cr-Mn alloys.The segregation of Fe often leads to the formation of ferrite.This fact isbeneficial to reducing the swelling rate and segregation on the grain boundaries. 相似文献
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几种微量元素在高温合金中的作用与机理 总被引:4,自引:0,他引:4
郭建亭 《中国有色金属学报》2011,21(3)
研究几种微量元素对高温合金力学性能和微观组织结构的影响;从晶界结合力、晶界沉淀和凝固偏析等方面对微量元素的不同作用进行讨论.结果表明:适量的B、C、Y、La、Ce、Zr和Mg明显改善高温合金的持久性能;Si和S则明显降低高温合金的持久性能;而P对一些高温合金特别是变形高温合金表现出有益作用,而对另一些高温合金特别是铸造合金表现出有害作用. 相似文献
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S. A. Starikov A. R. Kuznetsov V. V. Sagaradze V. A. Pechenkin I. A. Stepanov 《The Physics of Metals and Metallography》2010,109(4):376-382
The process of nickel segregation at grain boundaries in the Fe-Cr-Ni alloy upon severe plastic deformation has been investigated
depending on the temperature. The kinetics of the formation of segregates has been studied by numerically solving diffusion
equations that take into account the generation and absorption of point defects and their mutual recombination. It has been
shown that the Ni concentration at grain boundaries is reduced with increasing temperature and at T ≥ 600 K no segregates are formed, which agrees with the experiment. The dependence of the degree of Ni segregation on the
rate of generation of point defects is nonmonotonic, with a maximum in the range of medium rates of generation, which qualitatively
corresponds to the analogous dependence observed upon radiation-induced segregation of nickel in this alloy. 相似文献