Al-Zn-Mg-Cu合金时效过程的小角度x射线散射研究

通过同步辐射小角度x射线散射方法（SAXS），研究了三种Al_Zn_ Mg_Cu合金沉淀析出过程显微结构参数（析出相尺寸和体积分数），随时效温度和时效时间 的演化，同时分析了Zn含量对合金沉淀析出过程的影响.结果表明，三种合金（A，B，C） 在实验条件下析出相均属于纳米尺度，析出相的最大体积分数随Zn含量的增加而增加，最大体积分数分别为0.023—0.028，0.052—0.054和0.04.在一定时效温度下，体积分数随时效时间的变化规律，符合析出相的形核、核长大和粗化动力学过程.  关键词： 小角度x射线散射 Al_Zn_Mg_Cu合金 时效 析出相尺寸 析出相体积分数     

小角x射线散射确定TiNi薄膜中晶化粒子的长大激活能

用小角x射线散射技术研究以直流磁控溅射方法制备TiNi合金薄膜其退火生成的晶化粒子的长大行为.发现在室温下溅射的TiNi合金薄膜存在小于1nm尺寸的微空洞,将退火后薄膜的小角x射线散射强度扣除退火前微空洞产生的小角x射线散射强度,用这种方法得到的散射强度遵从Porod定律;而用通常方法扣除背底得到的散射强度结果不满足Porod定律.TiNi合金薄膜在733—793K之间退火晶化粒子的长大激活能Eg=301kJmol. 关键词： TiNi薄膜 晶化粒子 长大激活能     

Al-Li合金时效-回归-再时效析出δ′相的行为

应用小角X射线散射技术研究二元Al-Li(Li的质量分数为2.70%)合金时效-回归-再时效析出δ′相的行为.发现再时效8h析出的δ′相与基体之间存在明显的过渡界面层,再时效16h以后过渡界面层消失.表明δ′相粒子的长大首先是吞噬过渡界面层长大,然后是互相吞并长大. 关键词： Al-Li合金 时效－回归－再时效 过渡界面层     

用原位x射线小角散射研究块体非晶合金Zr55Cu30Al10 Ni5的结构弛豫

应用同步辐射x射线小角散射法在原位对块体非晶合金Zr₅₅Cu₃₀Al ₁₀Ni₅在等温退火过程中的微结构变化进行研究.实验表明：在等温退火过程中电子 密度涨落反映了晶化之前的结构弛豫过程；在一定的退火温度下、随退火时间的增加，拓扑短程序弛豫与化学短程序弛豫之间存在一个电子密度均匀化的过程；导致这两种弛豫过程转变的退火时间与退火温度有关，温度越高，所需的退火时间越短. 关键词： 原位x射线小角散射 块体非晶合金 等温退火 结构弛豫     

7050铝合金等通道转角挤压过程中显微结构和力学性能演化的小角x射线散射研究

采用三种等通道转角挤压（ECAP）与热处理相结合的工艺制备了超高强度细晶7050铝合金， 应用小角x射线散射技术定量地分析了ECAP过程中显微结构参数的变化情况，合理地解释了E CAP过程中力学性能的变化，揭示了合金强化机理. 研究发现，“固溶淬火＋ECAP＋时效” 工艺是获得高性能7050铝合金的合适工艺，可以使7050铝合金的抗拉强度提高到677 MPa， 延伸率保持在15％左右. 关键词： 7050铝合金 小角x射线散射 显微结构 力学性能     

块体非晶合金Zr55Cu30Al10Ni5 结构弛豫的研究

应用同步辐射小角x射线散射和差示扫描量热分析对块体非晶合金Zr55₅₅Cu 30₃₀Al10₁₀Ni5₅结构弛豫进行了研究.实验结果表 明：经340℃、不同时间退火后的非晶内 部的电子密度涨落随退火时间的延长先增大而后减小；玻璃转变温度附近焓弛豫峰的表观激 活能则随退火时间的延长先减小而后增大.结果反映了随退火时间的延长，块体非晶合金内 部类液体区不断减少及类固体区不断增加的过程. 关键词： 小角x射线散射 块体非晶合金 结构弛豫     

回火金属玻璃小角X射线散射强度的背底校正

提出校正回火金属玻璃（非晶合金）小角ｘ射线散射强度的背底误差的方法：将淬火态非晶合金的小角Ｘ射线散射强度作为在相同的实验条件下得到的回火非晶合金小角Ｘ射线散射强度的背底而予以扣除。并将这样扣除背底和用通常方法扣除背底得到的结果相比较，由前者得到的散射强度遵从Ｐｏｒｏｄ律，并进而得到Ｐｏｒｏｄ常数Ｋ_p＝４．６×１０^-2（ｎｍ^-3），积分不变量Q_s＝１．６３（ｎｍ^-2），比内表面Ｓ_p＝８４ｍ²／ｃｍ³，Ｐｏｒｏｄ半径Ｒ_p＝４．４ｎｍ用通常方法扣除背底后的散射强度不满足Ｐｏｒｏｄ规律。 关键词：     

蠕变镍基单晶高温合金微观结构与界面特征的X射线小角散射研究

利用SAXS技术对蠕变过程中不同尺度范围的微观结构变化分析表明X射线小角散射(SAXS)与中子小角散射(SANS)测量的二维散射图具有明显的差异,由散射强度曲线的变化说明了蠕变过程中二次析出γ'相形貌和不同区域尺寸特征的改变情况.分析结果表明二次析出γ'相存在两类特征尺寸,在蠕变过程中沿[100]或[010]方向的变化趋势类似,均是在第一和第二阶段有所减小,在第三阶段又有所增大,相较而言,特征尺寸较大的γ'相变化也较为显著.二次析出γ'相在蠕变第二阶段元素扩散最严重,相表面最粗糙,在第三阶段两相界面又进一 关键词： 单晶高温合金 二次析出γ'相 X射线小角散射 微观结构     

退火诱导亚稳态Fe80Cu20合金固溶体的结构相变

利用扩展x射线吸收精细结构和x射线衍射研究了机械合金化制备的体心立方(bcc)的亚稳态Fe₈₀Cu₂₀合金固溶体的结构随退火温度的变化特点.结果表明，在300—873 K温度范围内，随着退火温度的升高，bcc结构物相的晶格常数近于线性降低，这主要是由于Cu原子从bcc结构Fe₈₀Cu₂₀合金固溶体中逐渐偏析出来，生成面心立方(fcc)结构的Cu物相所致.经603K退火后，Cu原子的平均键长R_Cu—Cu增加了0.003 nm左右，大约有50%的Cu原子从bcc结构的Fe₈₀Cu₂₀合金固溶体中偏析出来.在773 K退火后，bcc结构Fe_８０Cu₂₀合金固溶体近于完全相分离，生成了bcc结构的α-Fe与fcc结构的Cu物相. 关键词： 扩展x射线吸收精细结构 x射线衍射 ８０Cu₂₀合金')" href="#">Fe_８０Cu₂₀合金 机械合金化     

Cu60Zr30Ti10非晶合金弛豫和晶化过程的小角X射线散射研究

应用小角X射线散射技术研究了Cu₆₀Zr₃₀Ti₁₀非晶合金从300到813 K之间微结构的演化情况.发现在淬火状态下Cu₆₀Zr₃₀Ti₁₀非晶合金中存在直径30 nm左右的富Cu区.非晶的结构弛豫包括573 K之前的低温结构弛豫和573 K到玻璃转变温度的高温结构弛豫，弛豫的结果是产生含有有序原子团簇的富Cu区，这些有序原子团簇的富Cu区是随后晶化过程中晶核产生的基础.Porod曲线分析表明，晶化生成的纳米体心立方CuZr相和基体之间有明锐的界面. 关键词： 小角X射线散射 非晶合金 结构弛豫 晶化     

Optical absorption and fluorescence investigation of the precipitated phases of Eu2+ in KBr single crystals

Europium precipitation in monocrystalline KBR has been studied using optical absorption and photoluminescence techniques. The annealing of quenched samples at temperatures below 100°C produces the growth of an emission band peaking at 433 nm which appears to be related with the presence of Suzuki-type precipitates in the crystals. The aging at higher temperatures, however, produces the appearence in the emission spectrum of two other bands peaking at 427 and 459 nm. The data presented in this paper strongly suggest that the former band is associated with the stable dihalide phase EuBr₂ in the host KBr, while the latter is due to a metastable precipitate whose structure appears to be quite similar to that of europium bromide. Some of the characteristics of the second phase precipitates were obtained by measuring the crystal field splitting (10 Dq) of the 4f⁶5d configuration of the Eu²⁺ ions in each one of them.     

A Subnanoscale Investigation of Sb Segregation at MnO/Ag Ceramic/Metal Interfaces

We have studied Sb segregation at MnO/Ag(Sb) ceramic/metal heterophase interfaces employing three-dimensional atom-probe (3DAP) microscopy. Specimens are prepared by the internal oxidation of Ag(Mn) alloys, leading to the formation of nanometer-size MnO precipitates within a Ag(Mn) matrix. Sb is introduced into the internally oxidized specimens with a vapor diffusion treatment. Appreciable Sb segregation is observed only after a subsequent segregation anneal is performed, and the measured interfacial excess of Sb at the MnO/Ag(Sb) interfaces, _Sb ^MnO/Ag, is determined directly. The temporal evolution of the MnO precipitates is followed for the different processing steps employed. It is shown that the concentration of silver within the MnO precipitates decreases from an initial value of 45–50 at.% Ag to less than 5 at.% Ag with increasing annealing time at the different processing temperatures. Thus the MnO precipitates form under paraequilibrium conditions and the precipitates inherit Ag from the matrix. With increasing aging time orthoequilibrium conditions prevail and the MnO precipitates reject the silver atoms they inherited from the matrix.     

Effects of aging temperature on G-phase precipitation and ferrite-phase decomposition in duplex stainless steel

G-phase precipitation and ferrite-phase decomposition in a cast duplex stainless steel (DSS) aged at 623–723?K for up to 8000?h were investigated using atom probe tomography (APT). Large sample volume was observed in every APT experiment, which yielded significantly statistical results. The number density of G-phase precipitates tended to be high and their sizes were small at lower aging temperatures. G-phase precipitates grew during prolonged isothermal aging. The concentrations of nickel, silicon, manganese and molybdenum in G-phase precipitates tended to increase as the precipitates grew. Heterogeneous distributions of alloying elements within G-phase precipitates were observed. An interesting positional relationship of G-phase precipitates with dislocations was revealed. Regarding the ferrite-phase decomposition, local chromium concentrations in the ferrite phase varied fast at higher aging temperatures. Good correlation between the variation of local chromium concentrations and aging conditions was revealed, which indicates that the variation can be estimated for arbitrary aging conditions. Representative distances between chromium-enriched and chromium-diluted regions were long at higher aging temperatures. Time exponent of the representative distances of ferrite-phase decomposition as well as the size of G-phase precipitates increased with aging temperatures.     

Effect of precipitates on thermal conductivity of aged Mg-5Sn alloy

Abstract

The influence of precipitates on thermal conductivity of aged Mg-5Sn alloy has been investigated at different heat treatment temperatures. The results show that the thermal conductivity of aged Mg-5Sn alloy increases from 87.5 to 92.8 W·m^?1·K^?1 at 433 K for 720 h and from 87.5 to 122 W·m^?1·K^?1 at 513 K for 120 h with the increasing ageing time. The increasing rate of the former is obviously lower than that of the latter. Meanwhile, the Sn content of precipitates at 433 K is considerably below that of aged Mg-5Sn at 513 K. The interface between precipitates and α-Mg matrix is completely coherent at 433 K for 720 h. The increase in thermal conductivity is mainly attributed to the remaining Sn solutes in α-Mg matrix, and the interface relationship between precipitates and α-Mg matrix.     

Performance improvement of electrochromic display devices employing micro-size precipitates of tungsten oxide

In this paper, we studied the effect of micro-size WO₃ precipitates on the electrochromic characteristics based on aging test. The electrochromic mechanism can be effectively investigated by a solid-state TaN/WO₃/ITO capacitor. The experimental results reveal that WO₃ electrochromic devices with optimized aging time of 4 days exhibit a higher optical contrast and longer retention time, which is mainly attributed to the formation of micro-size WO₃ precipitates during aging process. The performance improvement using micro-size WO₃ precipitates has the potential in future large-area window or energy efficient display applications.     

Study of precipitation in NaCl:Pb2+ by light scattering and ultramicroscopy

The formation and dissolution behaviour of precipitates in NaCl : Pb²⁺ single crystals is studied by light scattering and ultramicroscopy. Measurements of Rayleigh ratio together with ultramicroscopic observations during isochronal annealing indicate the presence of two types of precipitates in as-grown crystals. Isochronal annealing after suitable thermal and thermomechanical treatments shows that precipitates of first type (I) which form and dissolve at lower temperatures, are due to homogeneous nucleation. Precipitates of the second category (II) which form and dissolve at higher temperatures are aligned along crystallographic directions and have their origin in stress-assisted processes. Isothermal annealing has been used to study the dissolution kinetics of the precipitated fraction, and it is found that the kinetics is of first order. The enthalpy of solution is determined from a study of the temperature dependence of the kinetic rate constant, in conjunction with available information on the migration energy of Pb²⁺ in NaCl. The enthalpy so deduced is in good agreement with the value as usually obtained from the concentration dependence of the dissolution temperature.     

An optically detected magnetic resonance study of manganese-doped silver chloride

ODMR spectra have been observed in manganese-doped AgCl crystals and precipitates at low temperatures. During crystal growth from the melt or during annealing some of the Mn²⁺ is converted to Mn³⁺, which is an electron trap. The low-temperature luminescence is interpretated as recombination between self-trapped holes and [Mn²⁺nV_Ag] donors.     

Investigation of ruthenium Schottky contacts to n-GaAs

Ruthenium was evaporated on n-GaAs to form Schottky contacts. Initial electrical measurements revealed a near ideal Schottky behaviour with low leakage currents. The Schottky diodes exhibit good stability upon thermal aging at elevated temperatures up to 300° C. However, the diode parameters rapidly deteriorate after aging at temperatures in excess of 400° C. The room temperature (300 K) median life of the diodes, based on a failure criterion of a tenfold increase in the diode saturation current, J _riv ^s , from reverse bias current-voltage (I–V) data, was of the order of 10⁴ h.     

Preparation and luminescence properties of Y2(WO4)3: Eu3+

A red-emitting Y₂(WO₄)₃: Eu³⁺ phosphor (orthorhombic high temperature phase, anhydride) is prepared by two different methods: the firing of mixtures of constituent oxides and that of precipitates from aqueous solutions. After optimizing preparation conditions, the cathodoluminescence brightness reaches 56% that of Y₂O₂S: Eu³⁺, a commercial red phosphor for color TV. Formation of a high temperature phase below the reported transition temperature is noted in the fired precipitates. This phase occurrence is shown to depend on the treatment of the precipitates to be fired. Reflection difference measurement of Eu-doped and undoped samples assigns an excitation band of about 245 nm to the Eu-O charge transfer band. Different by-products in the two preparation methods are identified by measuring emission spectra under selective excitation. Reversible hydration-dehydration of the phosphor is demonstrated by successively measuring photoluminescence first in vacuum and then in air at various temperatures. No deterioration of luminescence efficiency is observed after repeating this reversible structural change.     

Effect of oxidizing anneals on thermochemically reduced MgO:Ni crystals

Oxidizing anneals have been carried out to test the stability of nickel precipitates previously formed in MgO:Ni by thermochemical reduction. The annealed crystals have been examined by transmission electron microscopy (TEM) and cathodoluminescence (CL). Both techniques, TEM and CL, reveal that the nickel precipitates become unstable under oxidizing annealing at temperatures 1223 K for 30 min. Cathodoluminescence results are analyzed on the basis of anion vacancy complexes and Ni²⁺ transitions.