High Temperature Corrosion of Fe-25Cr and Fe-17Cr-1.5Si-0.5Al Alloys in Oxidizing and Sulfidizing Enviornments

The simultaneous oxidation and sulfidation of Fe 25Cr and Fe-17Cr-l.5Si-0.5Al alloys was studied at 1023K and 1223K in H2-H2O-H2S gas mixtures. The kinetic boundary which indicates the transition from oxide to sulfide has heen found in these two alloys. The critical oxygen partial pressures of Fel7Crl.5SiO.5Al alloys were systematically lower than those of Fe-25Cr alloy. The reaction kinetics were measured by the stainless steel spring balance, and the reaction products were characterized by X-ray diffraction and scanning electron microscopy. The reaction rate usually decreased with the increase of the oxygen partial pressure at the constant sulfur partial pressure. The exista-nce of silicon plays an important role to suppress the sulfidation of Fel7Cr alloy.     

Wettability and pressureless infiltration mechanism in SiC-Cu systems

The wetting behavior of copper alloys on SiC substrates was studied by a sessile drop technique. The microstructure of SiC_p/Cu composites and the pressureless infiltration mechanism were analyzed. The results indicate that Ti and Cr are effective elements to improve the wettability, while Ni, Fe, and Al have minor influence on the improvement of wettability. Non-wetting to wetting transition occurs at 1210 and 1190℃ for Cu-3Al-3Ni-9Si and Cu-3Si-2Al-1Ti, respectively. All the copper alloys react with SiC at the interface forming a reaction layer except for Cu-3Al-3Ni-9Si. High Si content favors the suppression of interracial reaction. The infiltration mechanism during pressureless infiltration is attributed to the decomposition of SiC. The beneficial effect of Fe, Ni, and Al is to favor the dissolution of SiC. The real active element during pressureless infiltration is Si.     

Structure and corrosion resistance of Al–Cu–Fe alloys

The microstructure and electrochemical properties of Al–Cu–Fe alloys with the atomic compositions of Al_(65)Cu_(20)Fe_(15),Al_(78)Cu_7Fe_(15)and Al_(80)Cu_5Fe_(14)Si_1have been studied.The alloys were produced by induction melting of pure elements with copper mold casting.The microstructure of the alloys was analyzed by X-ray diffraction and high-resolution transmission electron microscopy.The formation of quasicrystalline phases in the Al–Cu–Fe alloys was confirmed.The presence of intermetallic phases was observed in the alloys after crystallization in a form of ingots and plates.The electrochemical measurements were conducted in 3.5%NaCl solution.The electronic structure of the alloys was determined by X-ray photoelectron spectroscopy.The post corrosion surface of the samples was checked using a scanning electron microscope equipped with the energydispersive X-ray detector.It was observed that the Al_(65)Cu_(20)Fe_(15)alloy had the highest corrosion resistance.The improved corrosion resistance parameters were noted for the plate samples rather than those in the as-cast state.And the hardness of the Al_(65)Cu_(20)Fe_(15)alloy was significantly higher than the other alloy samples.     

Studies on induction hardening of powder-metallurgy-processed Fe-Cr/Mo alloys

Induction hardening of dense Fe-Cr/Mo alloys processed via the powder-metallurgy route was studied. The Fe-3Cr-0.5Mo, Fe-1.5Cr-0.2Mo, and Fe-0.85Mo pre-alloyed powders were mixed with 0.4wt%, 0.6wt%, and 0.8wt% C and compacted at 500, 600, and 700 MPa, respectively. The compacts were sintered at 1473 K for 1 h and then cooled at 6 K/min. Ferrite with pearlite was mostly observed in the sintered alloys with 0.4wt% C, whereas a carbide network was also present in the alloys with 0.8wt% C. Graphite at prior particle boundaries led to deterioration of the mechanical properties of alloys with 0.8wt% C, whereas no significant induction hardening was achieved in alloys with 0.4wt% C. Among the investigated samples, alloys with 0.6wt% C exhibited the highest strength and ductility and were found to be suitable for induction hardening. The hardening was carried out at a frequency of 2.0 kHz for 2-3 s. A case depth of 2.5 mm was achieved while maintaining the bulk (interior) hardness of approximately HV 230. A martensitic structure was observed on the outer periphery of the samples. The hardness varied from HV 600 to HV 375 from the sample surface to the interior of the case hardened region. The best combination of properties and hardening depth was achieved in case of the Fe-1.5Cr-0.2Mo alloy with 0.6wt% C.     

Macrosegregation and the underlying mechanism in Ti-6.5Al-1.0Cr-0.5Fe-6.0Mo-3.0Sn-4.0Zr alloy

A novel method for the analysis of composition distribution of titanium alloys over a large area(64 mm × 72 mm) was investigated by exploring the original position statistic distribution based on spark spectrum(OPA-SS) in Ti-6.5 Al-1.0 Cr-0.5 Fe-6.0 Mo-3.0-Sn-4.0 Zr titanium alloy. The results showed that OPA-SS could characterize the distribution of elements in different positions on the titanium alloy. The macrosegregation of Sn was the most pronounced, with a statistic segregation degree higher than 18%; the macrosegregation of Mo followed with a statistic segregation degree of 10%; the macrosegregation of Al and Fe was relatively milder,lower than 8%. The main reason for the macrosegregation state of the as-cast Ti-6.5 Al-1.0 Cr-0.5 Fe-6.0 Mo-3.0 Sn-4.0 Zr alloy can be the solute redistribution during liquid solidification and the diffusion rate of each element in the solid phase.     

Effects of Yb^3＋ codoping on visible and near infrared emissions of Er^3＋-Yb^3＋ codoped Al2O3 powders by the sol-gel method

The 0.1 mol% Er^3＋ and 0-2 mol% Yb^3＋ codoped Al2O3 powders were prepared by the sol-gel method, and the phase structure, including only two crystalline types of doped Al2O3 phase, γ-（Al,Er, Yb）2O3 and θ-（Al,Er, Yb）2O3, was detected at the sintering temperature of 1000℃. The visible and near infrared emissions properties depended strongly on the Yb^3＋ codoping, and the corresponding maximal peak intensities centered at about 523, 545, 660 and 1533 nm were obtained respectively for the 0.1 mol% Er^3＋ and 0.5 mol% Yb^3＋ codoped Al2O3 powders, which were composed of θ-（Al,Er,Yb）2O3 and a small amount of γ-（Al,Er, Yb）2O3 phases. The two-photon absorption process was responsible for the visible up-conversion emissions, and the one-photon absorption process was involved in the near infrared emissions of the Er^3＋-yb^3＋ codoped Al2O3 powders.     

Effect of homogenization process on the hardness of Zn–Al–Cu alloys

The effect of a homogenizing treatment on the hardness of as-cast Zn–Al–Cu alloys was investigated. Eight alloy compositions were prepared and homogenized at 350 ℃ for 180 h, and their Rockwell “B” hardness was subsequently measured. All the specimens were analyzed by X-ray diffraction and metallographically prepared for observation by optical microscopy and scanning electron microscopy. The results of the present work indicated that the hardness of both alloys (as-cast and homogenized) increased with increasing Al and Cu contents; this increased hardness is likely related to the presence of the θ and τ' phases. A regression equation was obtained to determine the hardness of the homogenized alloys as a function of their chemical composition and processing parameters, such as homogenization time and temperature, used in their preparation.     

Effects of high-pressure rheo-squeeze casting on the Fe-rich phases and mechanical properties of Al-17Si-(1,1.5)Fe alloys

The effects of high pressure rheo-squeeze casting(HPRC) on the Fe-rich phases(FRPs) and mechanical properties of Al-17 Si-(1,1.5)Fe alloys were investigated. The alloy melts were first treated by ultrasonic vibration(UV) and then formed by high-pressure squeeze casting(HPSC). The FRPs in the as-cast HPSC Al-17 Si-1 Fe alloys only contained a long, needle-shaped β-Al5 Fe Si phase at 0 MPa. In addition to the β-Al5 Fe Si phase, the HPSC Al-17 Si-1.5 Fe alloy also contained the plate-shaped δ-Al4 Fe Si2 phase. A fine, block-shaped δ-Al4 Fe Si2 phase was formed in the Al-17 Si-1 Fe alloy treated by UV. The size of FRPs decreased with increasing pressure. After UV treatment, solidification under pressure led to further refinement of the FRPs. Considering alloy samples of the same composition, the ultimate tensile strength(UTS) of the HPRC samples was higher than that of the HPSC samples, and the UTS increased with increasing pressure. The UTS of the Al-17 Si-1 Fe alloy formed by HPSC exceeded that of the Al-17 Si-1.5 Fe alloy formed in the same manner under the same pressure. Conversely, the UTS of the Al-17 Si-1 Fe alloy formed by HPRC decreased to a value lower than that of the Al-17 Si-1.5 Fe alloy formed in the same manner.     

Bulk nanocrystalline Al prepared by cryomilling

Bulk nanocrystalline Al was fabricated by mechanically milling at cryogenic temperature (cryomilling) and then by hot pressing in vacuum. By using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), the microstructure evolution of the material during cryomilling and consolidation was investigated. With increasing the milling time, the grain size decreased sharply and reduced to 42 nm when cryomilled for 12 h. The grains had grown up, and the columnar grain was formed under the hot pressing and extrusion compared with the cryomilled powders. The grain size of as-extruded specimen was approximately 300-500 nm. The reason of high thermal stability of this bulk was attributed primarily to the Zener pinning from the grain boundary of the AlN arising from cryomilling and the solute drag of the impurity. Tensile tests show that the strength of nanocrystalline Al is enhanced with decreasing grain size. The ultimate tensile strength and tensile elongation were 173 MPa and 17.5%, respectively. It appears that the measured high strength in the cryomilled Al is related to a grain-size effect, dispersion strengthening, and dislocation strengthening.     

Synthesis of a NiTi_2–AlNi–Al_2O_3 nanocomposite by mechanical alloying and heat treatment of Al–TiO_2–NiO

The aim of the present study was to investigate the phases formed during ball milling of Al–TiO_2–NiO. For this purpose, a mixture of Al–TiO_2–NiO with a molar ratio of 6:1:1 was used. Characterization of the milled powders by X-ray diffraction, differential thermal analysis, field-emission scanning electron microscopy, and transmission electron microscopy showed the formation of nanocrystalline NiTi_2 along with AlNi. A thermodynamical investigation confirmed that NiO was reduced by Al during ball milling, which consequently promoted TiO_2 reduction and the formation of NiTi_2. Al is capable of reducing NiO either during ball milling or at temperatures above the melting point of Al; by contrast, TiO_2 can be reduced by Al only by milling.     

Al含量对Fe-Al合金中微观缺陷和价电子密度的影响

测量Ｆｅ２８Ａｌ和Ｆｅ４０Ａｌ合金的正电子寿命谱参数,计算合金基体和缺陷处的价电子密度。Ｆｅ２８Ａｌ和Ｆｅ４０Ａｌ合金基体的价电子密度（ｎｂ）分别为４１０×１０－２ａｕ和２３６×１０－２ａｕ,表明当Ａｌ和Ｆｅ结合形成Ｆｅ２８Ａｌ或Ｆｅ４０Ａｌ合金时,Ａｌ原子提供价电子与Ｆｅ原子的３ｄ电子形成局域的共价键,Ｆｅ２８Ａｌ和Ｆｅ４０Ａｌ合金中金属键和共价键共存。两种合金均有开空间大的缺陷,晶界缺陷处价电子密度（ｎｄ）〔１３２×１０－３ａｕ（Ｆｅ２８Ａｌ）,４７０×１０－３ａｕ（Ｆｅ４０Ａｌ）〕比基体的低,表明晶界处的键合力较弱。Ｆｅ４０Ａｌ合金晶界缺陷的开空间比Ｆｅ２８Ａｌ的大。     

两种快凝AlFeX（V，W）Si合金的组织性能

采用喷射沉积坯轧制和ＲＳ／ＰＭ粉末挤压坯轧制的２种工艺制各了Ａｌ－８．５Ｆｅ－１．３Ｖ－１．７Ｓｉ和Ａｌ－８．５Ｆｅ－１．３Ｗ－１．７Ｓｉ合金的板材，并通过透射电镜，扫描电镜和力学拉伸实验研究了板材的组织性能．结果表明，综合性能ＡｌＦｅＷＳｉ合金优于ＡｌＦｅＶＳｉ合金的喷射沉积坯轧制板材．     

Fe3Al基合金在模拟汽车尾气气氛中的腐蚀行为

研究了Fe-28Al-5Cr,Fe-28Al-5Cr-0.5Nb-0.1C合金及其采用钨极氩弧焊接的Fe3Al基合金焊缝,在模拟汽车尾气气氛中的腐蚀行为,分析了腐蚀产物的组成及形成机理,并与目前在汽车尾气系统应用的A3央钢及1Cr18Ni9不锈钢进行对比,结果表明,由于在实验条件下Fe3Al基合金及其焊缝表面形成了一层致密的Al2O3氧化膜,与不锈钢相同,显示出优良的抗蚀性能,与此相对比,由于A3钢表面形成疏松的Fe2O3膜容易剥落,而使腐蚀加剧。     

Sintering mechanism of Cu-9Al alloy prepared from elemental powders

The sintering behavior of Cu-9Al alloys prepared from die pressing of elemental powders was investigated. The experimental results and kinetic analysis showed the formation of three consecutive layers of Al₂Cu, Al₄Cu₉, and AlCu phases, with Al₂Cu appearing first in the initial solid phase sintering stage. A liquid phase formed in the intermediate stage, resulting from the eutectic reaction between Al and Al₂Cu phases at 500 °C, which is 47 °C lower than the equilibrium reaction temperature. Swelling occurred when the liquid phase infiltrated the gaps between the copper particles, leaving pores at the original sites of Al particles and Al₂Cu. In the final stage of sintering, the Al-rich phases (Al₂Cu and AlCu) transformed to Al-poor phases (Al₄Cu₉ and α-Cu) in the temperature range of 500–565 °C. Al₄Cu₉ and α-Cu then transformed to AlCu₃ (β) above the eutectoid reaction temperature (565 °C), whereas AlCu₃ transformed to α-Cu and eutectoid phases (α-Cu + Al₄Cu₉) during cooling. The pure copper transformed to AlCu₃, and the pore volume decreased at 1000 °C. The microstructure study helps manipulate precisely the sintering process of Cu-Al alloys and optimize the microstructure with a high dimensional accuracy.     

Effects of high-pressure rheo-squeeze casting on the Fe-rich phases and mechanical properties of Al-17Si-(1,1.5)Fe alloys

The effects of high pressure rheo-squeeze casting (HPRC) on the Fe-rich phases (FRPs) and mechanical properties of Al-17Si-(1,1.5)Fe alloys were investigated. The alloy melts were first treated by ultrasonic vibration (UV) and then formed by high-pressure squeeze casting (HPSC). The FRPs in the as-cast HPSC Al-17Si-1Fe alloys only contained a long, needle-shaped β-Al₅FeSi phase at 0 MPa. In addition to the β-Al₅FeSi phase, the HPSC Al-17Si-1.5Fe alloy also contained the plate-shaped δ-Al₄FeSi₂ phase. A fine, block-shaped δ-Al₄FeSi₂ phase was formed in the Al-17Si-1Fe alloy treated by UV. The size of FRPs decreased with increasing pressure. After UV treatment, solidification under pressure led to further refinement of the FRPs. Considering alloy samples of the same composition, the ultimate tensile strength (UTS) of the HPRC samples was higher than that of the HPSC samples, and the UTS increased with increasing pressure. The UTS of the Al-17Si-1Fe alloy formed by HPSC exceeded that of the Al-17Si-1.5Fe alloy formed in the same manner under the same pressure. Conversely, the UTS of the Al-17Si-1Fe alloy formed by HPRC decreased to a value lower than that of the Al-17Si-1.5Fe alloy formed in the same manner.     

Oxidation behavior of the Fe-36Al-0.09C-0.09B-0.04Zr alloy at 1250°C

To explore and study the Fe-Al system alloy presenting exceptional oxidation resistance at high temperature, the Fe-36Al-0.09C-0.09B-0.04Zr alloy was designed and developed. The microstructure and hardness of the backing at 1250°C were analyzed and measured. Thermodynamics and kinetics of the oxidation behavior were also analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy techniques. The results show that the microstructure of the Fe-36Al-0.09C-0.09B-0.04Zr alloy is FeAl phase at ambient temperature and is stable at 1250°C. It displays the excellent property of oxidation resistance because the oxide film has only the Al₂O₃ layer, and its oxidation kinetics curve obeys the parabolic law at 1250°C. The oxidation mechanism at 1250°C is presumed that in the early oxidation period, the alloy oxidizes to form a large number of Al₂O₃ and a little Fe₂O₃, then, the enrichment of Al caused by Fe oxidization combines with O to form Al₂O₃.     

基于正交试验的高强高导AA8000系铝合金的优化设计

采用正交试验进行合金成分优化设计,运用二元搭配表得到最优的合金成分,研究了Fe、Si含量对AA8000系铝合金性能的影响.采用扫描电子显微镜（SEM）,X射线衍射仪（XRD）,金相显微镜（OM）和透射电子显微镜（TEM）,研究了Fe、Si及其交互作用对铝合金微观组织的影响.探究了不同的组织相貌对铝合金电学性能及力学性能的影响,并从理论上分析了Fe、Si的交互作用机理.研究结果表明：由正交试验得到最优的合金元素组成,当Fe的质量分数为0.4%,Si的质量分数为0.2%时,合金具有较高的导电率和较高的强度;Fe、Si存在交互作用,Fe与Si可以形成Al₈Fe₂Si三元中间相,减少了Si对铝合金导电性能的不利影响.     

交流磁场对Al-Fe合金凝固组织的影响

研究了交流磁场对Al-Fe合金中含铁相形态及分布的影响.近共晶Al-1.99%Fe(质量分数,下同)和亚共晶Al-0.90%Fe两种铝合金在3℃/min的冷却速率凝固过程中,施加强度为0.3 T,频率为20 Hz的交流磁场,并与未施加磁场的试样进行对比.实验结果表明,在这两种合金中,无论是先析出Al3Fe相还是先析出-αAl,施加交流磁场后,Al3Fe相均向试样的中心处富集.这是由于Al3Fe相的磁化率大于熔融铝基体的磁化率,使得Al3Fe相和铝基体相比受到指向样品轴线的更大的电磁力,从而导致其向试样中心处聚集.     

Speciation of the elements and compositions on the surfaces of dust storm particles： The evidence for the coupling of iron with sulfur in aerosol during the long-range transport

The speciation of the elements on the surface of the particles collected during dust storm and non-dust storm in Beijing and Inner Mongolia was studied by XPS. The major species of iron on the surface were oxides, sulfate, silicate,FeOOH and minor part sorbed on SiO2/Al2O3. Sulfate is the dominant species of sulfur on the surface. SiO2 and Al2O3 are the main components of Si and Al on the surface respectively.One of the most important findings was that the Fe(Ⅱ) (FeS and FeSO4) produced could account for up to 44.3% and 45.6% of the total Fe on the surface in the aerosol sample collected at that night and next day of the “peak” time of the dust storm occurring on March 20, 2002, while Fe2(SO4)3,one of the Fe(Ⅲ) species on the surface decreased from 67.1% to 49.5% and 48.0% respectively. Both S and Fe enriched on the surface of aerosol particles. Fe(Ⅱ) accounted for 1.3%-5.3% of total Fe in bulk aerosol samples during dust storm. These results provided strong evidence to support the hypothesis of the coupling between iron and sulfur in aerosols during the long-range transport, which would have important impact on the global biogeochemical cycle.