Microstructures of Thermomechanically Treated Eutectoid Zn-Al Alloy

A continuously cast eutectoid Zn-Al alloy was extruded at about 250℃ and the complex microstructures of three phases (α. ε and η'E) were observed in the extruded eutectoid Zn-Al alloy.The fcc Al-rich α phase appeared as isolated particles with clear boundaries instead of the α phase occurring with diffuse boundary within the dendrites of the as-cast structure. A new unstable phase η'E was determined to have hexagonal close packed crystal structure. The decomposed β's, phase comprised the matrix. The new phase η'E decompoeed and a four phase transformation α+ε T'+η occurred afterwards during the isothermal holding. The extruded alloy tended to be stable after these two phase transformations. The early shrinkage and the following increase in dimension were related to the decomposition of the new phase η'E and the four phase transformation.     

Tensile Stress Induced Phase Transformations in Zn-Al Alloy

Both furnace cooled and as-cast eutectoid Zn-Al alloys were investigated under external tensile stress at 100℃. It was observed that the external tensile stress caused decomposition of two metastable phases η'T and η'S which derived from both original state of the alloy, and a phase transformation, αf +ε→T' +η, in both furnace cooled and as-cast eutectoid Zn-Al alloys. Also spheroidized structure formed partially during tensile testing. Superplasticity of the alloy has been discussed correlating with the phase transformations and microstructural changes.     

Structural Changes of α Phase in Furnace Cooled Eutectoid Zn-Al Based Alloy

Furnace cooling is a slow cooling process. It is of importance to study structural evolution and its effects on the properties of alloys during the furnace cooling. Decomposition of aluminium rich α phase in a furnace cooled eutectoid Zn-Al based alloy was studied by transmission electron microscopy. Two kinds of precipitates in the α phase were detected in the FCZA22 alloy during ageing at 170℃. One was the hcp transitional α＂ m phase which aooears as directional rods and the round precipitates. The other was the fcc α＇m phase. 〈101〉. The orientation relationship between the a phase and transitional phase α＇m was determined as （022）α＇m （fcc）//（022^-）α（fcc）, [1^-11]α＇m, （fcc）//[2^-33]α（fcc）. The non-equilibrium phase decomposition of the α phase is discussed in correlation with the equilibrium phase relationships.     

Creep Induced Phase Transformation in Extruded Zn-Al Alloy

Phase transformation and microstructural change of an extruded eutectoid Zn-Al alloy Zn76Al22Cu2 (wt pct) were investigated during creep testing by using SEM and X-ray diffraction techniques. Creep induced decomposition of a metastable η'T phase and a four phase transformation, α+ ε →T' +η, occurred during the creep testing. Also a microstructural change was observed from a lamellar structure into a spheroidized structure in the rupture part of the extruded alloy. It provided evidence of creep induced phase transformations which occurred in ageing process. The mechanism of creep rupture of the extruded Zn-Al alloy was also discussed.     

Decomposition Reactions in a Quench-aged Eutectoid Zn-Al Base Alloy AlZn75Cu3Si2

As a part of the systematical investigation of thephase relationships of the Zn-Al base alloys,decomposi-tion of the supersaturated phase β_S in a eutectoidZn-Al-Cu-Si alloy was studied by hardness testing,opti-cal,electron microscopy and X-ray diffraction.Com-pared to the monotectoid Zn-Al-Cu-Si alloy,a similarsequence of decomposition was found to consist of threestages of phase transformation,which were in accordanceto various equilibrium reactions at the temperatures abovethe ageing temperatures.     

Creep-induced phase transformations in furnace cooled Zn-Al alloy

Phase transformation and microstructural change of a furnace-cooled eutectoid Zn-Al alloy specimen (76 wt% Zn-22 wt% Al-2 wt% Cu) were investigated during creep testing by using scanning electron microscopy and X-ray diffraction techniques. Creep-induced decomposition of a metastable η′T phase and a four-phase transformation, α+ε→T′+η, occurred during the creep testing. Also microstructural change was observed from a lammellar structure partially into a spheroidized structure in the rupture part of the furnace-cooled alloy. The mechanism of the creep rupture of the furnace-cooled eutectoid Zn-Al alloy was also discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Phase transformations in nanocrystalline alloys synthesized by mechanical alloying

The effect of nanometer grain size and extensive grain boundary regions in nanocrystalline alloy systems was investigated for the chemical order-disorder, structural, precipitation, and spinodal phase transformations. The kinetic paths for approach to the chemically ordered phase from the disordered phase in FeCo-Mo alloys were observed to be the same at different temperatures due to grain boundaries acting as short-circuited diffusion paths for atom movements. The structure of Fe₃Ge was bcc for small crystallite size and the equilibrium fcc phase developed only after a critical grain size was attained. This was understood as a manifestation of the Gibbs Thomson effect. The precipitation phase transformation in Fe-Mo alloys proceeded by a rapid movement and clustering of the Mo atoms to the grain boundaries that was correlated to the size of the nano grains, and subsequent formation of the Mo rich lambda phase directly in the grain boundary regions. The composition fluctuation domains for spinodal decomposition in nanophase Fe-Cr alloys were observed to be linearly correlated to the growth of grains.     

The effect of HfO<Subscript>2</Subscript> second phase in Fe films upon ion irradiation

Ferrum of BCC crystal structure is a typical kind of matrix in structural alloy steels which could be strengthened by introducing some second phase. In the present study, BCC Fe thin films with hafnium oxide (HfO₂) second phase have been synthesized in an electron beam evaporation system. Multi-layered and glancing angle deposition (GLAD) techniques were taken to form some HfO₂ second phase in Fe films. Ion irradiation was conducted to investigate the irradiation resistance of the obtained samples with and without HfO₂ second phase.     

Phase Equilibria in Zn-Al-Cu-Si System at 285℃

As a part of the systematic investigationon phase relationships of Zn-Al based alloyscontaining Cu and/or Si, the equilibrium phasetransformations of the quaternary Zn-Al-Cu-Sisystem at 285℃ were investigated by using X-raydiffracti on, scanning electron microscopy andelectron probe microanalysis techniques. A five-phase of (α+β+εT'+σ) and a four-phase of (β+ε+η+σ) were detected separatelycoexisting in the Zn-Al-Cu-Si system at 285℃.Then the 285℃ isothermal section of Zn-Al-Cu-Sisystem (with 0.1% -Si content) was established,and an equilibrium reaction was determined at286℃ as the following pattern, β+T'=α+ε     

机械镀Zn-Al合金镀层的耐腐蚀性能研究

为了增强机械镀镀层的耐腐蚀性能,采用机械镀方法,以含铝5%(质量分数)的Zn-Al合金粉为原料,在Q235钢材基体表面制备了Zn-Al合金镀层。利用扫描电镜(SEM)表征了合金镀层的截面和断面形貌;采用极化曲线、电化学阻抗谱(EIS)分析了合金镀层在3.5%NaCl溶液中的电化学行为;通过中性盐雾腐蚀实验分析了合金镀层的耐蚀性,并采用XRD分析了镀层的盐雾腐蚀产物。结果表明,Zn-Al合金镀层由葫芦状的Zn-Al合金颗粒交错互嵌堆积而成,镀层颗粒之间以类似隼接的连接方式搭接“卡锁”;与机械镀Zn层相比,Zn-Al合金镀层的腐蚀电位正移了209 mV,腐蚀电流密度仅为纯Zn镀层的7.1%左右,极化电阻为纯Zn镀层的14倍;Zn-Al合金镀层的容抗弧半径明显大于纯Zn镀层的弧半径,且Q_dl较纯锌层减小;纯Zn镀层出现白锈和红锈的时间分别为24和362 h,而Zn-Al合金镀层出现白锈和红锈的时间为48和504 h。Zn-Al合金镀层的耐中性盐雾腐蚀性能明显优于纯Zn镀层,合金镀层对电荷转移具有更好的抑制作用,且Zn-Al合金镀层的腐蚀产物结构致密,可增强物理屏蔽功能。     

Mechanochemical synthesis and characterization of Ni<Subscript>25</Subscript>Te<Subscript>75</Subscript> nanocrystalline alloy

Ni₂₅Te₇₅ nanocrystalline alloy containing trigonal NiTe₂ and Te nanocrystals was prepared through mechanochemical processing of pure elemental tellurium and nickel powders in argon atmosphere. The Ni₂₅Te₇₅ samples processed from 3 h to 30 h milling times were characterized by X-ray powder diffraction, transmission electron microscopy, magnetization and Raman spectroscopy. Trigonal NiTe₂ crystals with average size of 16 nm can be obtained after only 3 h of processing time. For longer milling times, the trigonal NiTe₂ phase becomes majority (about 70% with 30% for nanometric Te and no pure Ni was detected) and its average crystallite size slightly increases to 20 nm. Transmission electron microscopy images and electron diffraction patterns confirm the nanometric size of the crystalline domains in the agglomerated particles. The magnetic properties of the Ni₂₅Te₇₅ powders are dependent on synthesis time, suggesting a paramagnetic behavior mainly associated with the NiTe₂ nanophase. Raman spectra showed peaks that can be associated with unreacted Te and tellurium oxides modes, but it also showed several modes that can be attributed to trigonal NiTe₂ nanophase. The high-pressure experiments showed no phase transitions for NiTe₂ up to 17 GPa and Te phase transitions from form I to forms II and III occurred simultaneously at 4.5 GPa, remaining up to 12 GPa; after that, only reflections of Te-III and the NiTe₂ were observed. All the phase transitions observed with pressure are reversible after decompression. The bulk modulus determined from the least-squares fit of first-order Murnaghan equation of states is 110 GPa for the NiTe₂ nanophase and 28 GPa for Te-I.     

β-Cyclodextrin-assisted preparation of hierarchical walnut-like CeOHCO3 and CeO2 mesocrystals

The hierarchical walnut-like CeOHCO₃ mesocrystals were prepared by a facile hydrothermal method under low temperature with β-cyclodextrin (β-CD) as assistant agent. The hierarchical walnut-like CeO₂ mesocrystals were obtained by thermal decomposition of CeOHCO₃ mesocrystals. The crystal phase, morphology, and structure of CeOHCO₃ and CeO₂ mesocrystals were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The time-dependent experimental results indicated that the morphology transformation from shuttle-like to walnut-like and the crystal phase transformation from orthorhombic to hexagonal simultaneously occurred in the formation processes of CeOHCO₃ mesocrystals. On the basis of the morphological and crystal phase evolution processes, the formation mechanism of hierarchical walnut-like CeOHCO₃ mesocrystals, including dissolution-recrystallization processes, was discussed. β-CD was believed to play an important role in the formation of the hierarchical walnut-like CeOHCO₃ mesocrystals. The effects of reaction temperature, β-CD amount, and concentration of reactants on the morphologies of the products were systematically studied. CeO₂ mesocrystals exhibited the distinct red-shift phenomenon in UV-vis absorption spectra.     

Ageing characteristics of furnace cooled eutectoid Zn-Al based alloy

Phase transformations and microstructural changes of a furnace cooled eutectoid Zn-Al based alloy were studied during ageing at 100 and 170°C using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Three phase transformations occurred in the furnace cooled eutectoid Zn-Al alloy. The metastable _FC phase decomposed during isothermal ageing. The four-phase transformation, + T + followed the discontinuous decomposition of the _FC phase. Typical morphologies of the decomposition of the _FC and phases were observed in scanning electron microscopy. Decomposition of Al-rich phase was observed during the prolonged ageing by transmission electron microscopy. The different types of decomposition of the different metastable phases dominated at different stages of ageing.     

粉末冶金法制备稀土锌铝合金的研究

本文研究了一种制备稀土锌铝合金的新方法——粉末冶金法(快速凝固技术 温压烧结技术)及其制备的合金的形貌与力学性能。利用金相显微镜和SEM研究了合金的形貌，利用EDS和XRD研究了合金的成分，并测定了合金的密度和硬度。本研究开拓了一种稀土锌铝合金材料制备的新方法；本方法制备的锌铝合金组织成分均匀，无偏析产生，且与传统脆性锌铝合金不同，其具有良好的塑性。本研究的稀土锌铝合会块材料比传统浇注法生产的锌铝合金的硬度更为均匀，且有10％～20％左右的提高；在密度方面，本方法制备的材料比传统的锌铝合金材料降低约16％。     

原位反应烧结块的高能超声稀释过程分析

对高能超声稀释原位反应烧结块制备锌铝合金基复合材料过程进行了研究,简要分析了超声稀释机理。研究表明,高能超声快速稀释烧结块是声空化与声流效应协同作用的结果。空化产生的瞬时高温可促进界面区域元素扩散,瞬时高压将裸露在界面上的长棒状的TiAl₃击断,打破了烧结块的网状结构,并将其周围的高致密度的Al₂O₃和TiB₂颗粒聚集区击碎。另一方面,声流引起的强烈搅拌作用减薄了过渡层,并使短棒状的TiAl₃颗粒及Al₂O₃、TiB₂微细颗粒均匀分布在熔体中。在上述分析基础上,建立了元素扩散模型和烧结块在锌铝合金中的稀释过程模型。      

Crystal orientation in CuSn-alloy coatings obtained by magnetron sputtering

Crystal orientation in copper-tin alloy coatings of different chemical composition as a function of substrate temperature has been studied using the X-ray texture goniometer technique. The coatings were obtained by magnetron sputtering an alloy target in argon at a gas pressure of 6 × 10⁻¹ Pa using two kinds of substrate—one of ferritic stainless steel and the other of a glass ceramic material. It has been established that Cu-Sn 7.8% alloy films, which represent an α-solution of Sn in Cu are textured. At low substrate temperature (710–770 K) the α-phase crystals have a mixed 〈100〉 and 〈110〉 orientation and at temperatures in the range from 870 to 1000 K—〈110〉 orientation. No orientation was detected when the condensation proceeded by the mechanism vapour→liquid→solid. The η-Cu₆Sn₅ and Sn phase crystals in CuSn 74% alloy films were not oriented.     

热喷涂Zn-Al合金防腐涂层技术的研究进展

热喷涂Zn-Al合金涂层技术是一项新发展起来的防腐技术.介绍了近年来分别利用火焰喷涂技术和电弧喷涂技术制备Zn-Al合金涂层及其喷涂材料的研究应用现状,分析了涂层的形成及其耐蚀机理,并展望了热喷涂Zn-Al合金涂层技术的发展趋势.     

The fabrication of light-emitting devices from hot-pressed ZnSe powders

A hot-pressing process was developed to synthesize fine ZnSe powders into compacts with high bulk density. The hot-pressed ZnSe powder compacts after an annealing treatment in the Zn-Al alloy melt were readily processed into light-emitting devices based on a metal-semiconductor (M-S) device structure. The fabricated devices are found to emit light in the orange region of the visible spectrum and have a room temperature quantum efficiency of the order of 10^–6 photons/electron in the reverse direction. The photoluminescence and electroluminescence characteristics of the hot-pressed ZnSe powder compacts are also found to be very similar to those observed in single crystal material.     

Mechanical Milling Induced Preferred Orientation in a Zn-Al Based Alloy

Mechanical milling resulted in the preferred orientation of the Zn-rich metastable hep εη'_FC and η'_γ phases in the furnace cooled (FC) eutectoid Zn-Al based alloy filings, after hot rolling or elevated temperature tensile-creep. The milling induced preferred orientation for the Zn-rich ε phase, and theεη'_FC and η'_γ phases in the eutectoid alloy were at (0002) and 10&lmacr;0 crystal planes respectively, which reverted the original, 0 h milling state orientation as the directional external stress was destroyed during further milling.     

Growth of nanocomposite in eutectic Cu-Ag films

Eutectic composition Cu-Ag alloy thin films were prepared by co-deposition at room temperature onto oxidized Si substrates by thermal evaporation. Morphological development, structure and phase state of the films were investigated by transmission electron microscopy. The films possess fibre morphology 10-30 nm in diameter and strong <111> texture is present. The fibres are nanocrystalline composed of 2-3 nm size zones of Cu and Ag rich solid solution phases and a model for morphological development and phase separation is described. In the early stages of growth phase separation occurs by nucleation in melted islands and a eutectic of randomly oriented crystallites forms. In later stages of growth the phase separation takes place by spinodal decomposition. It results in a strain stabilized unique morphology corresponding to an intermediate stage of phase separation.