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.     

Al-Zn-Mg基合金多级时效不同热处理阶段的析出行为研究

采用X射线衍射仪(XRD)和附带能谱仪(EDAX)的扫描透射电子显微镜(STEM)对Al-4.6Zn-0.9Mg合金三级时效工艺过程中强化相析出行为进行了系统研究。结果表明,100℃单级时效合金强度优于120℃单级时效;三级时效的再时效过程中,由于二级时效温度不同,合金内析出相的种类、尺寸及分布有显著差异;多级时效过程中如果二级时效温度位于300℃～400℃之间,第一级时效形成的析出相会溶解,且在再时效前期合金元素在晶界处显著偏聚,尽管在该回归温度区间内时效,很多析出相会溶解,但其中的合金元素并没有完全扩散开,依然留下了某种成份偏聚。这些偏聚的原子集团不能在后续再时效过程中重新形成GPII区。这使得再时效时析出相成核数量很少但粗化速度非常快,材料强度偏低。     

Al-Mg-Si-Cu合金中晶界和晶内析出相粗化规律的研究

采用显微硬度测试仪、扫描电镜和透射电镜观察及能谱分析,研究了Al-0.5Mg-1.0Si-0.8Cu(wt.%)合金的晶界析出规律和晶内析出相的粗化机制。结果表明:180℃时效处理的Al-0.5Mg-1.0Si-0.8Cu(wt.%)合金晶界处存在富Si相和Q相两类不连续分布的析出相,它们的尺寸分别约为1 mm和几十纳米;时效0.5 h时晶界处有少量富Si相,时效5 h时晶界富Si相明显增多,时效36 h时富Si相开始粗化且间距变大,再进一步时效其形貌和分布变化不大;晶界Q相与相邻晶粒铝基体的界面取向关系是:[510]Al//[1120]Q;时效36 h晶内开始出现粗化析出相,且随时效继续进行合金晶内析出大量粗化相,存在明显的晶界无析出带现象。晶内粗化析出相主要含有Si元素,呈片状、球状和棒状3种形貌。其中,棒状Si析出相是沿〈001〉Al方向生长的,且〈112〉Si//〈001〉Al,{111}Si//{010}Al。     

不同热处理工艺对Al-3.8Zn-1.6Mg铝合金微结构 与腐蚀行为作用的探讨

本文针对一种经历了三级时效后获得优良力学性能的7N01铝合金,采用慢应变速率拉伸、剥落腐蚀测试,并采用透射电镜系统研究了该合金局部腐蚀行为与微观结构的关系.结果表明,三级时效状态的7N01铝合金,相比直接热处理(T4、T5、T6)的材料,其抗应力腐蚀性能和抗剥落腐蚀性能均可获得显著提高.透射电镜观察发现:T4状态合金中晶界析出相以细小的GP区以及溶质原子团簇为主,且晶界处元素分布均匀;T5状态合金中晶界析出相粗大,存在晶界无析出带(PFZ),Zn、Mg元素于晶界析出相处富集;T6状态合金中晶界析出相细小且接近连续分布,Zn、Mg元素于晶界析出相处富集;虽然三级时效工艺后Zn、Mg元素也于晶界析出相处富集,但晶界析出相粗大且断续程度加大,形成较宽的耐腐蚀的PFZ,因此有着更好的抗腐蚀性能.     

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。     

自然时效和Cu含量对AlMgSi（Cu）合金时效硬化行为的影响

利用硬度测试和透射电子显微镜观察,对Cu含量分别为0.0%、0.15%、0.8%（wt.%）的AlMgSi合金进行了较系统地显微组织结构和时效硬化行为研究。热处理状态为固溶淬火后直接180℃人工时效及固溶淬火后自然时效两周再180℃人工时效。结果表明：添加Cu可以抑制自然时效对180℃人工时效硬度峰值的负面作用;与固溶淬火后先自然时效两周再180℃人工时效峰值样品比较,固溶淬火后直接180℃人工时效峰值样品中针状析出相的数量密度较大;含0.15%Cu的合金峰值时效样品中只观察到β″析出相,而含0.8%Cu的合金峰值时效样品中观察到β″和Q″析出相;与不含Cu和含0.15%Cu的合金比较,含0.8%Cu的合金时效峰值出现时间延迟。这种现象与Q″相的析出有关,因为析出Q″相需要额外的时效时间。     

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...     

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。     

Photoluminescence spectra of Si1-xGex/Si quantum well structures grown by three different techniques

Photoluminescence (PL) spectra of Si_1-xGe_x/Si multiple quantum wells have been measured at 4.2 K for the samples grown by three different techniques; conventional molecular beam epitaxy (MBE), gas-source MBE, and ultra high vacuum chemical vapor deposition (UHV-CVD). Only in the case of conventional MBE, strong emission bands appear about 80 meV below the band gap of Si_1-xGe_x. These strong emission bands disappear after the annealing at 800° C. From the dependence of the PL intensity on the excitation power, strong emission is considered to be due to some recombination center. On the other hand, in the case of gas-source MBE and UHV-CVD, the strong emission bands are undetectable, although the band-edge PL lines of Si_1-xGe_x are clearly observed. There is no significant change in the PL spectra after the annealing. The origin of the strong emission band is considered to be defects which are characteristic of conventional MBE.     

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.     

Conduction type and defect levels of β-FeSi2 films grown by MBE with different Si/Fe ratios

[1 0 0]-oriented β-FeSi₂ films were grown on Si(0 0 1) substrates by molecular beam epitaxy (MBE) with a deposited Si to Fe atomic ratio (Si/Fe ratio) varied from 1.6 to 2.8. It was found that the conduction type of the β-FeSi₂ films changed from p- to n-type between the deposited Si/Fe=2.4 and 2.8. Rutherford Back Scattering (RBS) measurements revealed that the real Si/Fe ratio of β-FeSi₂ is 2.0–2.1 for all the samples after 900°C annealing for 14 h, showing that stoichiometry of the grown films is almost satisfied even though the deposited Si/Fe ratio was away from stoichiometry.     

Valence-band offsets in strained SiGeSn/Si layers with different tin contents

Admittance spectroscopy is used to study hole states in Si_0.7–y Ge_0.3Sn _y /Si quantum wells in the tin content range y = 0.04–0.1. It is found that the hole binding energy increases with tin content. The hole size-quantization energies in structures containing a pseudomorphic Si_0.7–y Ge_0.3Sn _y layer in the Si matrix are determined using the 6-band kp method. The valence-band offset at the Si_0.7–y Ge_0.3Sn _y heterointerface is determined by combining the numerical calculation results and experimental data. It is found that the dependence of the experimental values of the valence-band offsets between pseudomorphic Si_0.7–y Ge_0.3Sn _y layers and Si on the tin content is described by the expression ΔE _V ^exp = (0.21 ± 0.01) + (3.35 ± 7.8 × 10^–4)y eV.     

Potentialities and basic principles of controlling the plastic relaxation of GeSi/Si and Ge/Si films with stepwise variation in the composition

GeSi/Si heterostructures consisting of a plastically relaxed layer that includes various fractions of Ge and which is grown on Si (001) span the values of the lattice parameter from equal to that in silicon to equal to that in germanium. The corresponding substrates are conventionally referred to as artificial. A number of methods exist for growing high-quality GeSi layers with as large as 100% of Ge on Si (001) substrates through an intermediate GeSi layer with a varying composition. However, it is desirable in a number of cases to have ultrathin (<1 μm) GeSi and Ge layers directly on the Si (001) substrate for practical applications. The results of new methods such as the use of a buffer Si layer grown at a comparatively low temperature (300–400°C) in plastic relaxation of the GeSi/Si(001) heterostructures and also the use of surfactants (antimony and hydrogen) are analyzed. The examples of artificial introduction of centers for origination of misfit dislocations as an alternative to their introduction from the rough surface are considered. It can be concluded that, in order to expand the range of potentialities of growing perfect plastically relaxed GeSi (001) films, it is necessary to (i) make it possible to form in a controlled manner the centers for origination of the misfit dislocations and (ii) retard or completely suppress the transition of the growth mechanism from two-to three-dimensional in order to prevent the formation of additional misfit dislocations from the surface of the stressed film and, correspondingly, additional threading dislocations.     

A study in flip-chip UBM/bump reliability with effects of SnPb solder composition

This paper aims to investigate the electromigration phenomenon of under-bump-metallization (UBM) and solder bumps of a flip-chip package under high temperature operation life test (HTOL). UBM is a thin film Al/Ni(V)/Cu metal stack of 1.5 μm; while bump material consists of Sn/37Pb, Sn/90Pb, and Sn/95Pb solder. Current densities of 2500 and 5000 A/cm² and ambient temperatures of 150–160 °C are applied to study their impact on electromigration. It is observed that bump temperature has more significant influence than current density does to bump failures. Owing to its higher melting point characteristics and less content of Sn phase, Sn/95Pb solder bumps are observed to have 13-fold improvement in Mean-Time-To-Failure (MTTF) than that of eutectic Sn/37Pb. Individual bump resistance history is calculated to evaluate UBM/bump degradation. The measured resistance increase is from bumps with electrical current flowing upward into UBM/bump interface (cathode), while bumps having opposite current polarity cause only minor resistance change. The identified failure sites and modes from aforementioned high resistance bumps reveal structural damages at the region of UBM and UBM/bump interface in forms of solder cracking or delamination. Effects of current polarity and crowding are key factors to observed electromigration behavior of flip-chip packages.     

A comparison of the sensing characteristics of long period gratings written in three different types of fiber

This paper compares the environmental sensing behaviour of long period gratings written in three fibers with different refractive index profiles: step, W and a progressive three layered fiber. The measurands considered are temperature, refractive index, axial strain and bending, and the spectral behaviour of individual attenuation bands were observed and, where possible, compared to theoretical predictions. Significant differences in the behaviour of the three fiber types were found.     

A comparison of thin film microrefrigerators based on Si/SiGe superlattice and bulk SiGe

Most of the conventional thermal management techniques can be used to cool the whole chip. Since thermal design requirements are mostly driven by the peak temperatures, reducing or eliminating hot spots could alleviate the design requirements for the whole package. Monolithic solid-state microcoolers offer an attractive way to eliminate hot spots. In this paper, we review theoretical and experimental cooling performance of silicon-based microrefrigerators on a chip. Both Si/SiGe superlattice and also bulk SiGe thin film devices have been fabricated and characterized. Direct measurement of the cooling along with material characterization allows us to extract the key factors limiting the performance of these microrefrigerators. Although Si/SiGe superlattice has larger thermoelectric power factor, the maximum cooling of thin film refrigerators based on SiGe alloys are comparable to that of superlattices. This is due to the fact that the superlattice thermal conductivity is larger than bulk SiGe alloy by about 30%.     

A diffraction study of a heteroepitaxial system-Ag/Si(111)

Epitaxial films of Ag(111) were grown by molecular beam epitaxy (MBE) on small angle misoriented Si(111) substrates. The surface normal is tilted 0 to 6° away from the Si(111) axis in the [112] direction. Despite a 25% lattice mismatch, good quality 600-1200Å thick Ag films were grown on Si. The structure of the interface has been examined using transmission electron microscopy (TEM). Through a detailed analysis of the TEM diffraction data (SADP-selected area diffraction pattern) from planar as well as cross-sectional samples, we can determine the epitaxial relationship between Ag and Si. This includes the small tilt of individual Ag islands on Si, the periodicity of the finite terraces in Si, and the size of the ordered regions in Ag. The O-lattice formalism of Bollmann is applied to this system and compared with the experimental observations.