关于FeCrAl合金中α'相的TEM研究

对经过475～540℃时效的Fe-(15～25)Cr-(4～5)Al合金进行了TEM研究,观察到球形富Cr-α'相粒子从α相基体均匀析出.在475℃时效1000h后粒子的平均直径约8nm,间距约14nm.电子衍射斑点沿圆弧分裂和拉长,这表明α'相开始脱离与α相的共格关系,但在长时间内两相仍有〈001〉、〈111〉或〈011〉等晶向大体平行的取向关系.     

碳化物强化粉冶钼合金

本研究制取了碳化物强化的粉末冶金钼合金丝，结果表明，混料中加入还原剂（硼和／或碳）形成的难熔碳化物粒子具有稳定作用，析出物的弥散强化的形成提高了变形硬化的能力，迟滞了回复、多边化和再结晶过程，细化了变形纤维或者再结晶晶粒的尺寸，与其他粉冶钼合金丝比，瞬时和持久强度较高。     

Mg-Gd-Y合金时效初期析出结构的形成和演变

本文利用原子分辨的高角环形暗场扫描透射电镜(HADDF-STEM)成像技术并结合第一性原理计算的方法研究了Mg97 Gd2 Y1(at.％)合金200℃时效初期结构的形成和演变过程.结果表明,合金时效初期优先形成与富稀土原子柱近邻组合关联的各种纳米级细小富稀土团簇.这些由富稀土原子柱构建的团簇可以通过分解、重组而转变成...     

AlCuMgAg合金时效后的择优纳米析出相

Al-Cu-Mg系合金是一种时效强化型合金。该系合金作为航空航天工业中的基础材料已有几十年的历史，但它还在不断的发展和完善。在高Cu：Mg比率的Al-Cu-Mg合金中加入微量的舷，会促进在{111}。面上形成一种均匀分布的片状Ω相，不但会提高时效强化效果，而且会改变合金的时效过程。细小的Ω相的均匀分布使得Al-Cu-Mg-Ag系合金在200℃时具有良好的热稳定性，因此该系合金被广泛用于航空航天结构材料。     

关于FeCrAl合金中α′相的TEM研究

对经过４７５￣５４０℃时效的Ｆｅ－（１５－２５）Ｃｒ－（４￣５）Ａｌ合金进行了Ｔ ＥＭ研究,观察到球形富Ｃｒ－α′相基体均匀析出。在４７５℃时效１０００ｈ后粒子的平均直径约８ｎｍ,间距约１４ｎｍ。电子衍射斑点沿圆弧分裂和拉长,这表明α′相开始脱离与α相的共格关系,但在长时间内两相仍有〈００１〉、〈１１１〉或〈０１１〉等晶 向大体平行的取向关系。     

一种镍基单晶高温合金中碳化物热稳定性研究

利用SEM、TEM研究了一种镍基单晶高温合金中碳化物在950℃时效不同时间的退化规律。固溶处理过程中形成的MC碳化物随时效时间的增加而逐渐退化为M6 C和M23 C6碳化物。同时,由于在时效处理过程中Re元素进入M6 C碳化物中,破坏了其结构稳定性,促使M6 C碳化物也可以退化为M23 C6碳化物。至时效3000 h时,没有观察到碳化物退化的逆反应。本研究可以为高温合金高温下服役的稳定性提供实验参考。     

Cu-Cr-Zr合金时效析出相的研究

利用高分辨电子显微镜（HRTEM）及系列欠焦像出射波函数重构技术,探明了在大气环境下,Cu-Cr-Zr合金峰值时效时存在氧化物析出相。研究结果表明：Cu-Cr-Zr合金经950℃×1.5 h固溶处理、450℃时效6 h硬度达峰值;此时样品中除早期的具有花瓣状应变场衬度的共格析出相外,另一类强化相为圆盘状形貌的CuCrO2;该氧化物析出相为三方晶系,空间群为R 3 m（166）,与基体具有特定取向关系：[011]Cu//[010]CuCrO2,（111）Cu//（003）CuCrO2,惯习面为{111}Cu。     

高速钢中马氏体及晶界碳化物析出规律研究

当高速钢发生马氏体相变时马氏体针的惯析面有很大的分散度;当淬火温度过高时,沿奥氏体晶界有碳化物呈链状析出。这是从事高碳高合金钢研究的电镜工作者都普遍知道的现象。但是由于较高速钢的电子衍射花样在大多数状态下都是复杂的多相,多晶重叠衍射花样,难于分解、分析。因此高速钢中马氏体惯析面的分散规律,沿奥氏体晶界碳化物的析出规律至今尚未进行深入的分析和测量本研究工作使用电子显微镜及用于多相、多晶分析的复杂重叠衍射花样分析方法。在进行了有高速钢精细结构研究的基楚上开展上述二个问题的分析工作。分析表明:     

多级时效对Al-Mg-Si(Cu)合金力学性能和显微结构的影响

本文通过透射电镜观察、差示扫描量热分析(DSC)和硬度测试等方法研究了6061铝合金在多级时效处理过程中力学性能和显微结构演变的规律.其中,T6I6热处理为先进行固溶处理,淬火后进行180℃预时效,然后在65℃中断时效,最后在180℃再次时效,120/T6I6热处理则将预时效温度改为120℃.结果表明,T6I6热处理不会明显提高合金的峰值硬度,合金强度与析出相类型、尺寸和分布有关系.120℃预时效后中断时效时继续形成GP区或β″前驱相,而180℃预时效后中断时效对显微结构的影响较小.120/T6I6的中断时效过程析出的主要是尺寸较小的GP区或β″前驱相,它们在再时效阶段不能成为析出相的形核点.T6I6在中断时效前GP区和β″前驱相基本全部析出.T6I6热处理和120/T6I6热处理均没有使峰值硬度明显增加,而且120/T6I6会拖延峰值时间.     

HAADF-STEM study on the early stage of precipitation in aged Al-Ag alloys

We report on the structure of Ag precipitates in aged Al-Ag alloys using transmission electron microscopy and high-angle annular detector darkfield scanning transmission electron microscopy (HAADF-STEM). Irregularly shaped small Ag particles of 1-2 nm dominate the alloy annealed at 140 degrees C for 10 h. These particles are present also within large precipitates (10-50 nm), which are often characterized by their {100} and {110} facets. In addition, atomic-resolution HAADF-STEM images revealed that Ag atoms tend to form {111} planar clusters, which criss-cross a colony of the irregularly shaped small Ag precipitates.     

低碳钢中纳米尺度沉淀相的透射电子显微术研究

本文用电子显微镜技术对CSP工艺生产的普通低碳钢进行了研究，实验结果表明在试样中形成了大量细小的弥散沉淀粒子，电子衍射与XEDS分析证实这些沉淀是具有尖晶石结构的氧化铁以及硫化物，氧化物尺寸在20nm以下，大量分布在晶界和位错上。晶界上还有尺寸在100－400nm左右的硫化物粒子。这些沉淀使低碳钢的强度提高近一倍，同时塑性也大幅增高。     

Crystallization properties of Sb-rich GeSbTe alloys by in-situ morphological and electrical analysis

Phase Change Memory (PCM) operation relies on the reversible transition between two stable states (amorphous and crystalline) of a chalcogenide material, mainly of composition Ge₂Sb₂Te₅ (GST). In Wall type PCM cells, cycling endurance induces a gradual change of the cell electrical parameters caused by variations in the chemical composition of the active volume. The region closer to the GST-heater contact area, becomes more Sb rich and Ge depleted. The new alloy has usually different thermal characteristics for the phase transitions that influence the electrical behavior of the cell. In this study we analyze the morphological, structural and electrical properties of two Sb-rich non-stoichiometric alloys: Ge₁₄Sb₃₅Te₅₁ and Ge₁₄Sb₄₉Te₃₇, at their amorphous and crystalline phase. Experiments have been performed in non-patterned blanket films and, to simulate the device size, in amorphous regions of 20 nm, 50 nm and 100 nm diameter respectively. The amorphous Ge₁₄Sb₃₅Te₅₁ film crystallizes in the meta-stable face centered cubic structure at 150 °C and in the rhombohedral phase at 175 °C, behavior characteristic of the Ge₁Sb₂Te₄ composition. The average grain size is of about 100 nm after an annealing at 400 °C. The Ge₁₄Sb₄₉Te₃₇ film crystallizes only in the hexagonal phase, with an average grain size of about 60 nm after annealing at 400 °C. The X-ray fluorescence analysis shows a non uniform distribution of the constituent atoms and in particular a Ge signal decrement and a Sb enrichment at grain boundaries. The in situ annealing of amorphous nano-areas (RESET state under a thermal stress) indicates a fast re-crystallization speed for Ge₁₄Sb₃₅Te₅₁, 80 pm/s at 90 °C, and a lower speed for Ge₁₄Sb₄₉Te₃₇, at 130 °C a grain growth velocity of 50 pm/s has been measured. The different behavior of the two alloys is discussed in terms of structural vacancies filling by the Sb atoms in excess and by their segregation at grain boundaries. The influence of the obtained results on the device characteristics is discussed.     

Theory of te precipitation and related effects in CdTe Crystals

A thermodynamic calculation is presented which explains the origin of often reported large stress fields in and around Te precipitates and associated punching of dislocation loops in star like patterns. The calculation is based on the consideration that the stoichiometric deviation in Te saturated crystals are accommodated by Te interstitials, Cd multivacancy complexes and Te antisites; the Te interstitials are most mobile of them, and dominate the precipitation process; and the precipitates when they appear first are in droplet form. The droplet state is modelled on the basis of the Lennard-Jones 6-12 interaction potential. The droplet growth is envisaged to occur via the following two processes operating in tandem: first, capture of excess Te interstitials to cause droplet overpressurization, and then, punching of interstitial dislocation loops whenever the pressure exceeds a threshold value. The flow of Te interstitials into the droplets is driven by the difference between their formation energies in the lattice and the free energy change of the droplets per Te atom added. It is shown that the achievable droplet pressures far exceed that required for the loop punching and sustaining the growth cycle. The occurrence of varying precipitate morphologies are explained, and the possibility of nucleating high presssure Te phases is examined. Some experimental evidence is also presented which corroborate the theoretical arguments involved.     

Effects of Cu, Ag and Sb on the creep-rupture strength of lead-free solder alloys

The materials used in the present research are pure Sn metal and Sn-0.5% Cu, Sn-3.5%Ag, Sn-0.3%Sb, and Sn-3.5%Ag-0.5%Cu alloys. Effects of Cu, Ag and Sb on the creep-rupture strength of lead-free solder alloys have been investigated. Creep tests are performed at the stress and temperature range of 3 to 12 MPa and 378 to 403 K, respectively. A 3.5% addition of Ag had the largest contribution to the creep-rupture strength of Sn metal among the single addition of 0.5%Cu, 3.5%Ag, and 0.3%Sb. The combined addition of 3.5%Ag and 0.5%Cu makes the largest creep-rupture strength. The effects of these elements on the microstructure of the lead-free alloys are also investigated with optical microscope (OM) and transmission electron microscope (TEM) observations.     

The influence of OMVPE growth pressure on the morphology, compensation, and doping of GaN and related alloys

Growth pressure has a dramatic influence on the grain size, transport characteristics, optical recombination processes, and alloy composition of GaN and AlGaN films. We report on systematic studies which have been performed in a close spaced showerhead reactor and a vertical quartz tube reactor, which demonstrate increased grain size with increased growth pressure. Data suggesting the compensating nature of grain boundaries in GaN films is presented, and the impact of grain size on high mobility silicon-doped GaN and highly resistive unintentionally doped GaN films is discussed. We detail the influence of pressure on AlGaN film growth, and show how AlGaN must be grown at pressures which are lower than those used for the growth of optimized GaN films. By controlling growth pressure, we have grown high electron mobility transistor (HEMT) device structures having highly resistive (10⁵ Ω-cm) isolation layers, room temperature sheet carrier concentrations of 1.2×10¹³ cm⁻² and mobilities of 1500 cm²/Vs, and reduced trapping effects in fabricated devices.     

Molecular beam epitaxy of CdSe and the derivative alloys Zn1−x Cd x Se and Cd1−x M x Se

We report the epitaxial growth of CdSe, Zn_1−x Cd _x Se (0 ≤x ≤ 1) and Cd_1−x Mn _x Se (0 ≤x ≤ 0.8) on (100) GaAs. X-ray diffraction (XRD), electron diffraction and transmission electron microscopy (TEM) indicate that all the epilayers have the cubic (zinc-blende) structure of the GaAs substrate. The energy gaps of these materials were measured using reflectivity measurements. We also report the growth of ZnSe/Zn_1−x Cd _x Se superlattices. TEM and XRD measurements show that high quality modulated structures with sharp interfaces are possible.     

Development of a high-strength high-conductivity Cu-Ni-P alloy. Part I: Characterization of precipitation products

The precipitation products of a Cu-1.5Ni-0.32P (wt.%) alloy isochronally aged at 400°C and 600°C were investigated by transmission electron microscopy (TEM). There are two different sizes of precipitates formed in the 600°C aged specimen. Large precipitates appear to be lath, the length of which varies from 100 nm to 500 nm, whereas small dotty contrasts around 10 nm in diameter are uniformly distributed in the matrix. Only small dotty contrasts are observed after 400°C aging. In the composition range 0–33.3 at.%P, both the previous studies and the calculated Ni-P binary phase diagram indicated that the possible nickel phosphide phases are Ni₃P, Ni₁₂P₅, Ni₅P₂, and Ni₂P. However, selected area electron diffraction (SAED) pattern analysis in conjunction with energy dispersive x-ray spectroscopy (EDS) identified the large lath precipitates as Ni₁₂P₅ phase. On the other hand, the small precipitates could not be analyzed by EDS due to thinness; thus, the structure is estimated to be a Ni₅P₄ phase from the relationships between d-spacing and angles between planes measured from a selected area diffraction pattern.     

7150铝合金时效时晶界析出行为的研究

本文采用透射电子显微镜(TEM)、能谱分析(EDAX)对人工时效条件下晶界无析出带(PFZ)的演变规律进行研究。实验选用同一投影方向测量PFZ的宽度,结果表明PFZ的宽度对时效温度的敏感性远远高于对时效时间的敏感性。时效温度越高PFZ越宽,而在同一时效温度下PFZ的宽度并不随时效时间的延长而宽化。PFZ的宽度与相邻两个晶粒之间的取向差有关系,在相同处理条件下,小角度晶界附近PFZ宽度小于大角晶界。能谱分析显示PFZ内为贫溶质原子区,Zn元素缺失尤为明显。     

7150铝合金时效时晶界析出行为的研究

本文采用透射电子显微镜(TEM)、能谱分析(EDAX)对人工时效条件下晶界无析出带(PFZ)的演变规律进行研究.实验选用同一投影方向测量PFZ的宽度,结果表明PFZ的宽度对时效温度的敏感性远远高于对时效时间的敏感性.时效温度越高PFZ越宽,而在同一时效温度下PFZ的宽度并不随时效时间的延长而宽化.PFZ的宽度与相邻两个...