ALCHEMI法测定有序合金的马氏体和贝氏体相的原子组态

虽然Ｃｕ－Ｚｎ－Ａｌ和Ｃｕ－Ａｕ－Ｚｎ合金中的母相已知为ＤＯ３或Ｌ２１结构，但通过通道增强微分析原子定位法（ＡＬＣＨＥＭＩ），可以检测Ｃｕ－Ｚｎ－Ａｌ合金的母相，马氏体相和Ｃｕ－Ａｕ－Ｚｎ合金的母相、马氏体、贝氏体相中的原子配置，结果表明，马氏体相中原子配置与母相是完全一样的，但Ｃｕ－Ｚｎ－Ａｌ合金听时效马氏体的Ｃｕ－Ａｕ－Ｚｎ合金中贝氏体与母相不同。本文叙述ＡＬＣＨＥＭＩ测定的结果。     

ZnO—MgO—Al2O3陶瓷性能研究

ＺｎＯ－ＭｇＯ－Ａｌ２Ｏ３陶瓷是一种复合烧结体，其主晶相为ＺｎＯ与ＺｎＡｌ２Ｏ４，且均以晶粒存在。ＭｇＯ能调节电阻温度系数，使之由负变为正。Ａｌ２Ｏ３能调节电阻率。慢的降温速度能提高线性及耐浪涌能量，降低电阻温度系数。     

组成对R_2O-CaO-ZnO-Al_2O_3-SiO_2系统分相的影响

通过大量的配方实验和ＯＭ、ＴＥＭ观察,系统研究了Ｒ２Ｏ－ＣａＯ－ＺｎＯ－Ａｌ２Ｏ３－ＳｉＯ２系统分相与组成间的相互关系．研究结果表明,Ｋ２Ｏ比Ｎａ２Ｏ更有利于系统的分相,用Ｎａ２Ｏ等摩尔取代Ｋ２Ｏ时,分相区向低铝高硅区收缩．此外,系统分相区大小还明显受到ＺｎＯ、ＣａＯ相对含量的影响,高锌系统具有更为宽广的分相区．Ａｌ２Ｏ３对Ｒ２Ｏ－ＣａＯ－ＺｎＯ－Ａｌ２Ｏ３－ＳｉＯ２系统分相影响呈现出明显的反常现象．在ＺｎＯ含量为０．５５ｍｏｌ的系统中,当Ｒ２Ｏ由０．１０ｍｏｌＫ２Ｏ＋０．１０ｍｏｌ Ｎａ２Ｏ共同引入时,分相区大小和分相结构尺度都呈现出明显的铝反常现象,而Ｒ２Ｏ仅由 ０．２０ｍｏｌＫ２Ｏ引入时;仅分相结构尺度呈现出明显的铝反常现象,反常点的 Ａｌ２Ｏ３含量约为 ６．２０ｍｏｌ％．在一定的热处理条件下,适当增加 ＳｉＯ２的含量有利于系统分相,但当 ＳｉＯ２的含量过高时,分相将由连通结构逐渐转变为孤立相分布于连续基质相中的液滴状结构,甚至消失．     

ZnO－MgO－Al_2O_3陶瓷性能研究

ＺｎＯ－ＭｇＯ－Ａｌ２Ｏ３陶瓷是一种复合烧结体，其主晶相为ＺｎＯ与ＺｎＡｌ２Ｏ４，且均以晶粒存在．ＭｇＯ能调节电阻温度系数，使之由负变为正．Ａｌ２Ｏ３能调节电阻率．慢的降温速度能提高线性及耐浪涌能量，降低电阻温度系数．     

化学气相沉积法制备ZnS块材料的相结合

用敢相沉积法制备了红外晶体ＺｎＳ块材料；分别用ＸＲＤ和ＴＥＭ分析了所沉积ＺｎＳ的相结构，并用ＩＲ测试了其红外透过率，结果表明：在沉积温度为５５０－７００℃，Ｈ２Ｓ／Ｚｎ摩尔流量比为０．５－２０的条件下所沉积ＺｎＳ的相结构主要为闪锌矿结构；随着沉积温度的升高和Ｈ２Ｓ／Ｚｎ摩尔流量比的增大，ＺｎＳ中有纤锌矿结构出现且其含量增多，导致了ＺｎＳ红外透过率的降低。     

La2O3—TiO2系陶瓷物相与介电性能研究

固相法合成Ｌａ２Ｏ３－ＴｉＯ２系陶瓷介质材料,ＸＲＤ、ＳＥＭ、ＥＤＳ分析其结构、形貌和成分。高精度电容测量仪测试其介电性能。Ｌａ２Ｏ３／ＴｉＯ２比１∶２、２∶１９组分可获得极低介质损耗,ＸＲＤ分析主晶相为Ｌａ２Ｔｉ２Ｏ７和Ｌａ４Ｔｉ９Ｏ２４。Ｌａ２Ｏ３／ＴｉＯ２比１∶３组分可获得Ｌａ２／３ＴｉＯ３、Ｌａ４Ｔｉ９Ｏ２４复相、缺陷型钙钛矿相Ｌａ２／３ＴｉＯ３不利于介质损耗降低。ＥＤＳ分析表明晶界富集Ｓｉ杂质,有效促进了液相烧结。     

锌镍合金镀层盐雾腐蚀行为的研究

研究了锌镍合金电层的盐雾腐蚀行为，结果表明，１２％－１６％Ｎｉ镀层不仅５％红锈出现时间长，红锈扩展慢，而出现腐蚀增重。ＳＥＭ、ＥＰＭＡ、ＡＥＳ和ＸＲＤ分析表明，锌镍合镀层的高耐蚀性和腐蚀增重与生成粘附力强、绝缘性好的腐蚀产物ＺｎＣｌ２．４Ｚｎ（ＯＨ）２和２ＺｎＣＯ３．３Ｚｎ（ＯＨ）２有关，腐蚀产物还密积堵塞了镀层在腐蚀过程生成的大量微裂纹。     

ZnO线性电阻性能研究

ＺｎＯ线性电阻是一种新型的以ＺｎＯ为主的陶瓷电阻。本文研究了降温速度和烧结温度对ＺｎＯ线性电阻性能的影响，利用ＳＥＭ、ＥＰＭＡ和ＸＲＤ等技术研究其微观结构及晶相组成，根据提出的ＺｎＯ线性电阻的导电模型，对有关现象给予解释。     

SiO2在ZnO—Bi2O3—Sb2O3—BaO系压敏陶瓷中的作用

ＳｉＯ２添加剂对ＺｎＯ－Ｂｉ２Ｏ３－Ｓｂ２Ｏ３－ＢａＯ系和通常的ＺｎＯ－Ｂｉ２Ｏ３－Ｓｂ２Ｏ３系压敏陶瓷电性能的作用和影响有很大不同。通过小电流区伏安特性，交变电压下复阻抗特性，以及对复电容平面图中半弧特性的分析可知，ＳｉＯ２对ＺｎＯ－Ｂｉ２Ｏ３－Ｓｂ２Ｏ３－ＢａＯ系压敏陶瓷中电性能影响是晶界组分及微结构变化造成的。     

K2O—B2O3—SiO2玻璃成分对析晶性能的影响

本文利用ＤＴＡ、ＸＲＤ、ＴＥＭ、ＳＥＭ等技术研究了三种Ｋ２Ｏ－Ｂ２Ｏ３－ＳｉＯ２玻璃的析晶性能。结果表明，Ｋ２Ｏ３－Ｂ２Ｏ３－ＳｉＯ２玻璃的析晶由分相引起，分相和析昌能力受成分影响较大，随Ｂ２Ｏ３和Ｋ２Ｏ含量增多及Ｋ２Ｏ／Ｂ２Ｏ３比值的降低，析晶加强，析晶主晶相类别尚未查清，次晶相确定为α－方石英。     

Atomic-resolution imaging of the nanoscale origin of toughness in rare-earth doped SiC

Ultrahigh-resolution transmission electron microscopy and atomic-scale spectroscopy are used to investigate the origin of the toughness in rare-earth doped silicon carbide (RE-SiC) by examining the mechanistic nature of the intergranular cracking events which we find to occur precisely along the RE-decorated interface between the SiC grains and the nanoscale grain-boundary phase. We conclude that, for optimal toughness, the relative elastic modulus across the grain-boundary phase and the interfacial fracture toughness are the most critical material parameters; both can be altered with judicious choice of rare-earth elements.     

On the formation of the diamond grain configuration during high temperature creep and fatigue

A study has been made of the influence of test variables on the formation of the diamond grain configuration during high temperature creep and fatigue deformation of a wide variety of metals. The proposed mechanisms for the formation of this interesting grain morphology are reviewed. It is concluded that the diamond grain configuration arises from a balance between grain-boundary sliding, grain-boundary mobility, intragranular deformation and defect imbalance across the grain boundaries and that it tends to be stabilized by intergranular cavitation. While the phenomenon occurs during high temperature fatigue in a variety of metals irrespective of their crystal structure, during creep it has been observed only in to h c p metals. It is surmised that the occurrence of the diamond array of grain boundaries during creep deformation in h c p metals is aided by the limited number of slip systems which leads to high defect imbalances in adjacent grains and consequently high driving forces for grain-boundary migration. On the basis of quantitative metallography involving measurements of the number of edges per grain section, the number of grains meeting at vertices, angular distribution histograms and grain-boundary lengths in different angular orientations with respect to the stress axis in "annealed" and "diamond" microstructures, it is concluded that the shape of the "diamond" grain is essentially the same as that of the "annealed" grain but in a distorted form.     

The microstructure of a ZnO varistor material

The microstructure of a ZnO varistor material has been investigated by a combination of X-ray diffractometry and analytical electron microscopy (SEM, TEM, STEM, EDX). The material was found to consist of: ZnO grains (doped with manganese, cobalt and nickel); smaller spinel grains which hinder the growth of ZnO grains during sintering; intergranular Bi-rich phases (namely -Bi₂O₃, pyrochlore and an amorphous phase); and a small proportion of ZnO-ZnO interfaces which did not have any intergranular film but to which bismuth had segregated. The intergranular microstructure is largely a result of processes which occur during liquid phase sintering and subsequent cooling to room temperature.     

非线性氧化锌变阻陶瓷的微观分析

用电子显微镜、电子探针和X射线衍射综合分析了多元掺杂ZnO压敏电阻陶瓷的微观结构和化学组成及其分布,探讨了掺杂对ZnO非线性伏安特性和浪涌吸收能力影响的微观机制。     

Improving the resistance to intergranular cracking and corrosion at elevated temperatures by grain-boundary-engineering-type processing

Failure of structural components operating under high mechanical loading and/or in aggressive environments can often be attributed to intergranular degradation, e.g. by creep, corrosion, fatigue or brittle cracking. The present article is focussed on oxygen-diffusion-controlled grain-boundary attack, for example, of a nickel-based superalloy leading to intercrystalline oxidation or rapid cracking by dynamic embrittlement. Since grain-boundary diffusion depends on the crystallographic orientation relationship between adjacent grains, the grain-boundary-engineering approach was applied to reduce the susceptibility to grain-boundary attack. The relevant mechanisms are discussed in terms of modifying the network of general high-angle and so-called special grain boundaries taking the results of cracking experiments on bicrystals into account.     

Initiation of recrystallized grain structure under high-temperature low-cycle fatigue in 304 stainless steel

Initiation of recrystallized grains was observed under high-temperature low-cycle fatigue conditions in austenitic 18Cr-8Ni stainless steel. The fatigue tests were carried out using unbalanced fast-tension and slow-compression triangular strain wave-shape at 973 K in air. Recrystallized grains were initiated and grew along grain boundaries with the number of fatigue cycles. Accumulated grain-boundary sliding is considered to be the driving force for the recrystallization. Effects of the recrystallized grain structure on high-temperature fatigue failure were then examined under the conditions in which intergranular fatigue failure occurred. The recrystallized grain structure had no detrimental effects on the intergranular failure. The fatigue life was somewhat increased by the initiation of recrystallized grain structure.     

新型ZnO陶瓷线性电阻材料

本文研究了少量ＭｇＯ，Ｌａ２Ｏ３，ＺｒＯ２等对ＺｎＯ陶瓷线性电阻材料晶粒生长速度和最终晶粒尺寸的影响规律，以及极微量掺杂Ｌｉ２Ｏ对晶粒和晶界电阻率的影响规律，实验表明，ＭｇＯ，Ｌａ２Ｏ３和ＺｒＯ２都能使ＺｎＯ陶瓷伏安特性线性化，在一定添加量范围内，ＭｇＯ的添加量不影响陶瓷线性电阻的电阻率，Ｌａ２Ｏ３和ＺｒＯ２的添加量都能有效地控制陶瓷线性电阻的电阻率，ＭｇＯ的添加量不影响ＺｎＯ陶瓷的晶粒生长速度，     

Effect of long-term electrical degradation on the distribution of donor impurities in ZnO varistor ceramics

The effect of long-term electrical degradation on the distribution of donor impurities in ZnO varistor ceramics and their electrical properties was examined. The results are consistent with the views that, in the initial stages of the process, the degradation is due mainly to local Joule heating at intergranular barriers, while at longer degradation times, the major mechanism of degradation is the redistribution of donors in the bulk of ZnO grains owing to their migration in the electric field of the barriers.     

Effects of grain-boundary GeO2 particles on intergranular fracture of Cu-GeO2 polycrystals

The Cu-GeO₂ alloy polycrystals containing plastically hard GeO₂ particles are tensile tested to study intergranular fracture behavior of the alloys at intermediate temperatures. The effects of large GeO₂ grain-boundary particles on the intergranular fracture are discussed using the specimens containing the particles of the fixed size (3 m in diameter) and different area-fractions. The ductility of the Cu-GeO₂ alloy polycrystals is larger than that of Cu polycrystals. The grain-boundary GeO₂ particles improve the ductility by suppressing grain-boundary sliding. The grain-boundary voids to cause theintergranular fracture preferentially nucleate between the grain-boundary GeO₂ particles. The ductility of the Cu-GeO₂ alloys increases with increasing the area fraction of the grain-boundary GeO₂ particles. The area-fraction dependence of the ductility is explained by considering the amount of GBS as a criterion of the intergranular fracture.     

Simulation of the behavior of a Σ5 grain boundary under combined thermal and external shear loading

The behavior of the grain boundary of a copper bicrystal under shear loading is studied by molecular dynamics simulation. The subject of the research is a high-angle boundary of the Σ = 5(210)[001] special type. The effect of the temperature of the sample on the characteristics of the behavior of the grain boundary under shear deformation is analyzed. It is shown that, in the sample heated above a certain temperature, the previously found mechanism of grain-boundary sliding in fcc crystals, which is accompanied by a simultaneous motion of the boundary in the direction perpendicular to the applied load, gives way to the conventional mechanism of grain-boundary sliding associated with the displacement of the grains relative to each other along the plane of the defect. The features of the change in the structure of the grain boundary upon a change in its response to shear deformation with increasing temperature are studied.