Effect of hydrogen on the mechanical behaviour of carbon-alloyed Fe3Al-based iron aluminides

The effect of hydrogen on the mechanical behaviour of two carbon-alloyed iron aluminides was studied. Weakening of some carbide-metal interfaces in the presence of hydrogen was indicated. The effect of cathodic hydrogen charging on the microstructure has also been addressed.     

On critical hydrogen concentration for hydrogen embrittlement of Fe3Al

The critical hydrogen concentration for hydrogen embrittlement in iron aluminide, Fe₃Al has been estimated (0.42 wppm). The estimated critical hydrogen content has been correlated to structural aspects of the decohesion mechanism of hydrogen embrittlement.     

Role of surface passive films in the hydrogen embrittlement of iron aluminides

The room temperature hydrogen embrittlement problem in iron aluminides has restricted their use as high temperature structural materials. Previous studies have established that surface films affect hydrogen embrittlement (HE). The effect of surface passive layer on the hydrogen embrittlement behaviour of iron aluminides has been critically reviewed in this presentation. The role of thermomechanical treatments in affecting the mechanical properties has been discussed from a processing-structure-properties correlation view point. The alloy development philosophy to yield ductile iron aluminides has been outlined based on this review. Novel iron aluminide intermetallics that are being currently synthesized and characterized along these lines at IIT Kanpur are finally introduced.     

Analysis of the diffusion processes in Al/Cr, Al/Fe and Cr/Fe multilayers using the MRI model

One of the methods for synthesis of intermetallic films consists of two steps: deposition of a multilayer film containing monometallic layers, and consequential annealing to induce a diffusion process and alloy formation. Though the diffusion coefficients are generally known for couples of common metals, they can considerably differ for films deposited by PVD due to their specific microstructure. Bimetallic multilayers Al/Cr, Al/Fe and Cr/Fe were analysed as the first step for formation of the complex metallic alloy Al₄(Cr,Fe). The films were deposited by triode sputtering with a total thickness of about 250 nm and consisted of 6 layers. Annealing was performed in vacuum at temperatures 240-650 °C.The depth distributions of elements in the films annealed at various temperatures were measured by Auger electron spectroscopy. Detailed analysis of the profile was conducted using the MRI model, which takes into account interface broadening of the measured profile due to three reasons: ion-induced atom mixing, roughness, and information depth of analysed electrons. Thus we reconstructed the true depth profile of the as-deposited samples and profiles of the annealed samples that allowed us to extract the diffusion coefficients.     

Cr对Cu-V氢分离合金组织与氢传输性能的影响

氢分离金属膜是目前备受关注的一种用于氢气提纯的功能材料.为了获得综合性能优异且价格低廉的氢分离金属膜,本文借鉴"多相构成、功能分担"的设计理念,通过非自耗电弧熔炼炉制备合金,采用XRD、扫描电子显微镜等手段研究合金相组成及微观组织,采用课题组自主设计的仪器设备在不同温度和压力下进行氢溶解和氢渗透实验,开发了具有双相结构的新型Cu-V-Cr氢分离合金.结果发现:该合金微观组织中的bcc-(V)固溶体相起渗氢作用,是氢的主要扩散通道;而组织中的fcc-(Cu)固溶体相起提高塑性作用.合金化元素Cr主要固溶在bcc-(V)中,显著降低合金的氢溶解能力,大幅度提高抗氢脆性能,但同时也降低合金的氢扩散系数和渗氢性能.实验表明,具有双相结构的Cu-V-Cr氢分离合金有望达到氢溶解、扩散和渗透性能的良好匹配,从而同时实现优异的氢渗透性能与抗氢脆性能.     

Effects of B+ and Cr+ ion implantation on the oxidation of Ni3Al

Ni₃Al samples were implanted with different doses of 150keV B⁺ and Cr⁺ ions to modify the surface region and the high-temperature oxidation behaviour was tested. The surface layer structure was investigated by Auger electron spectroscopy, and transmission electron microscopy, secondary ion mass spectroscopy and optical microscopy before and after testing. The experimental results show that boron atoms exist in the form of interstitial atoms. No evidence was found that any new phase existed in boron implanted Ni₃Al. Implanted Ni₃Al alloy has better oxidation resistance than the unimplanted ones at 900°C. For B⁺-implanted Ni₃Al, the oxide layer is basically composed of fine-grained NiO inner layer and an a-Al₂O₃ outer layer. Boron is oxidized into B₂0₃ of comparatively larger grain size. B₂0₃ particles are enriched at grain boundaries and defects. This curtails the short-circuit transportation of oxygen and improves the oxidation resistance of Ni₃Al. Implantation with Cr⁺ and B⁺ combines the good effects of both elements and produces a remarkable improvement on the oxidation resistance. The effects of implanted elements and the possible reaction mechanisms are discussed.     

Effect of Cr and Ni on diffusion bonding of Fe3Al with steel

Microstructure at the diffusion bonding interface between Fe₃Al and steel including Q235 low carbon steel and Cr18-Ni8 stainless steel was analysed and compared by means of scanning electron microscopy and transmission electron microscopy. The effect of Cr and Ni on microstructure at the Fe₃Al/steel diffusion bonding interface was discussed. The experimental results indicate that it is favourable for the diffusion of Cr and Ni at the interface to accelerate combination of Fe₃Al and steel during bonding. Therefore, the width of Fe₃Al/Cr18-Ni8 interface transition zone is more than that of Fe₃Al/Q235. And Fe₃Al dislocation couples with different distances, even dislocation net occurs at the Fe₃Al/Cr18-Ni8 interface because of the dispersive distribution of Cr and Ni in Fe₃Al phase.     

过渡金属离子掺杂对TiO2纳米尺寸及其相结构的影响

利用酸催化的溶胶-凝胶法合成了一系列不同掺杂量的Fe3 /TiO2、Cr3 /TiO2纳米复合微粒.用XRD和TEM研究了Fe3 、Cr3 的掺杂对TiO2纳米粒子尺寸和相结构的影响.结果表明:掺杂离子不同,对TiO2纳米粒子尺寸和相结构的影响不同.在所研究的掺杂量范围内(x:0.0000～0.1000),TiO2纳米粒子的粒径随Cr3 掺杂量的增加呈减小的趋势,但幅度不大;而Fe3 的掺杂则会引起TiO2粒子的团聚和晶粒的长大;由XRD分析可知:在掺杂量范围内,不会发生Fe2O3、Cr2O3等相的偏析,但Fe3 的掺杂引起了TiO2在低温条件下由锐钛矿向金红石的相转变.通过UV-Vis光谱的研究发现:Fe3 、Cr3 的加入,可以使TiO2对光的吸收拓展到可见区,同时随着掺杂量的增加,对可见光的吸收强度显著增强.     

Cr/Al复合合金化Fe_3Si基有序合金及其有序度研究

基于合金化的改性原理,以调整材料的长程有序度为改性思想,采用真空电弧熔炼/热压退火制备了四种Cr/Al复合合金化Fe3Si基有序合金。通过XRD,SEM,EPMA等对合金进行了表征,并采用长程有序参数定量表征了退火得到的有序相的有序程度。结果表明:四种不同成分的有序合金,具有不同的显微组织。随着Si含量降低合金有序度下降,且Cr/Al的复合效应对这一趋势起到了促进作用,使得具有相同Si含量的Fe65Si25Cr5Al5有序合金的有序度低于Fe3Si,分别为0.658和0.796。     

Cr、Ni元素对Fe3 Al/钢扩散焊界面组织结构的影响

采用扫描电镜和透射电镜分析比较了相同工艺条件下获得的Fe3 Al/Q235及Fe3 Al/Cr18-Ni8扩散焊界面的组织结构,研究了Cr、Ni元素对Fe3 Al/钢扩散焊界面组织结构的影响.研究表明:Cr、Ni的扩散有利于促进Fe3 Al与钢中Fe、A1元素的扩散结合,使Fe3 Al/Cr18-Ni8扩散焊界面过渡区的宽度较Fe3 Al/Q235界面过渡区大;并且Fe3 Al/Cr18-Ni8扩散焊界面过渡区新形成的Fe3 Al上弥散分布有含Cr、Ni的第二相,使Fe3A1出现了具有不同间距的位错对,甚至位错缠结现象,有利于提高Fe3 Al/钢扩散焊界面的结合强度.     

A new approach to the synthesis of nanostructured Fe3Al alloy and aluminum doped iron oxide material

Aluminum doped iron oxide nanostructured material with hematite phase has been produced by the heat-treatment process of an amorphous precursor under air atmosphere. The nano sized precursor was synthesized by using a co-precipitation method. The heat-treated product of the precursor under reduction atmosphere was Fe₃Al alloy with particle sizes around 200 nm. Powder X-ray diffraction pattern and Fourier transform infrared spectroscopy confirmed the formation of the products. That is, the intermetallic alloy, Fe₃Al has really produced via a wet chemical route for first time. Magnetic measurements indicated that all the samples are soft magnets with different magnetization.     

Effects of adsorbent dose, its particle size and initial arsenic concentration on the removal of arsenic, iron and manganese from simulated ground water by Fe3+ impregnated activated carbon

This paper presents the observations of the study on arsenic removal from a contaminated ground water (simulated) by adsorption onto Fe³⁺ impregnated granular activated carbon (GAC-Fe). Fe²⁺, Fe³⁺ and Mn²⁺ have also been considered along with arsenic species in the water sample. Similar study has also been done with untreated granular activated carbon (GAC) for comparison. The effects of adsorbent dose, particle size of adsorbent and initial arsenic concentration on the removal of As(T), As(III), As(V), Fe²⁺, Fe³⁺ and Mn²⁺ have been discussed. Under the experimental conditions, the optimum adsorbent doses for GAC-Fe and GAC have been found to be 8 g/l and 24 g/l, respectively with an agitation time of 15 h. Particle size of the adsorbents (both GAC and GAC-Fe) has shown negligible effect on the removal of arsenic and Fe species. However, for Mn removal the effect of adsorbent particle size is comparatively more. Percentage removal of As(T), As(V) and As(III) increase with the decrease in initial arsenic concentration (As₀). However, the increase in percentage removal of all the arsenic species with decrease in As₀ are less for higher value of As₀ (3000–500 ppb) than those of the lower value of As₀ (500–10 ppb). The % removal of As(T), As(III), As(V), Fe, and Mn were 95%, 92.4%, 97.6%, 99% and 41.2%, respectively when 8 g/l GAC-Fe was used at the As₀ value of 200 ppb. However, for GAC these values were 55.5%, 44%, 71%, 98% and 97%. The pH and temperature of the study were 7 ± 0.1 and 30 ± 1 °C, respectively.     

Diffusivity of Al and Fe near the diffusion bonding interface of Fe3Al with low carbon steel

The distribution of elements near the Fe₃Al/Q235 diffusion bonding interface was computed by the diffusion equation as well as measured by means of EPMA. The results indicated close agreement between the two for iron and aluminium. Diffusion coefficient in the interface transition zone is larger than that in the Fe₃Al and Q235 steel at the same temperature, which is favourable to elemental diffusion. The diffusion distance near the Fe₃Al/Q235 interface increased with increasing heating temperature,T , and the holding time, t. The relation between the width of the interface transition zone,x , and the holding time,t , conformed to parabolic growth law: x bd² = 4.8 × 10⁴ exp(-133/RT) bdt -t ₀bd. The width of the interface transition zone does not increase significantly for holding times beyond 60 min.     

CrO3对Fe2O3+Al铝热反应系统反应过程的影响

用铝热-重力分离法制备了不含铁铝尖晶石（FeAl₂O₄）的陶瓷内衬复合钢管,并通过热力学计算分析了有关反应的优先顺序,结果表明,在Fe₂O₃+Al系统中强氧化剂CrO₃与Al的反应并不是一步完成而是分步反应,FeAl₂O₄优先于Cr₂O₃与Al反应,因而加入CrO₃添加剂可有效地去除陶瓷层中的尖晶石相,从而提高复合钢管的耐蚀性能.     

Cr对Al-5%Fe合金中初生Al3Fe相形貌的影响

采用普通熔铸的方法研究了加Cr对Al-5%Fe合金铸态组织的影响,采用XRD方法分析了合金中的物相.结果表明,Cr可以明显改善合金中的初生Al3Fe相形貌.不加Cr时,合金中的初生Al3Fe相大多为针状、针片状,仅有少量为花朵状;加入0.2%～1.0%Cr,Al3Fe相转变为细小针状和针点状;Cr含量超过1.0%时,组织开始粗化,出现长针状和星状Al3Fe相.SEM扫描表明,Cr主要固溶在Al3Fe相中.XRD并未检测到含Cr化合物.     

退火对Cr3+离子掺杂Al2O3薄膜的结构及发光性能影响

用脉冲激光沉积技术在Si(100)基底上制备了纯Al2O3、掺杂浓度为0.3%、1%(质量分数)的Cr3+∶Al2O3薄膜。制备态的薄膜为立方γ-Al2O3结构,经800℃真空条件下退火1h样品的结晶度有所提高,呈现α-Al2O3相与γ-Al2O3相的衍射峰。薄膜基本保持了靶材中原有各元素成分比例,平均粒径为250nm,形貌为条形。与Al2O3粉体相比,制备态薄膜在386nm处的发光峰强度明显提高。这可归因于薄膜中氧空位的增加使双氧空位吸收电子所产生的F2+色心浓度提高。薄膜经真空退火后在332、398nm附近的发光峰强度明显增强,这是由于薄膜中氧空位的增加提高了F+、F色心浓度。与此同时,制备态薄膜在386nm附近发光峰经退火后由386nm蓝移至381nm,可归因于退火后制备态薄膜的内应力得到了释放。1%(质量分数)Cr3+掺杂薄膜在646、694nm出现Cr3+离子由4 T2能级跃迁至4 A2能级及由E-能级跃迁至4 A2能级产生的荧光发光峰。     

Influence of chromium concentration and particle size on the ESR linewidth of Al2O3: Cr3+ powders

The linewidth of electron spin resonance (ESR) absorption in polycrystalline samples of chromium-doped alumina (Al₂O₃: Cr³⁺) has been investigated as a function of chromium concentration and particle size. The linewidth is found to be directly proportional to chromium concentration and inversely proportional to particle size. The experimental results are consistent with the mechanism of dipolar broadening in diluted solid solutions; the influence of particle size may be attributed to size-dependent fluctuations of the zero-field parameter, D.     

Structural and photoluminescent properties of Al2O3: Cr3+ nanoparticles via solution combustion synthesis method

In the present work, we have discussed the structural and photoluminescent properties of Al₂O₃ nanoparticles doped with Cr³⁺ ion prepared through solution combustion synthesis (SCS) technique. SCS is a well-known method for the production of different metal oxides and composite materials such as metal matrix composites and for producing this need an extra reduction step. The set of samples differing in activator concentration were studied carefully by means of structural and optical characterization methods. In particular, the transmission electron microscopy (TEM) has been deployed together with X-ray diffraction (XRD) technique to determine fundamental structural properties of nanoparticles. XRD results showed that pure α-Al₂O₃ single phase was obtained and TEM result indicates that nanoparticles are spherical in shape. The selected area electron diffraction (SAED) and Energy dispersive analysis by X-rays (EDAX) analysis suggested the crystallinity and chemical composition of the Cr³⁺ doped Al₂O₃. The change in crystal structure parameters was obtained by Rietveld refinement method. The optical characterization focused mainly on the basic excitation and emission features and their sensitivity to the dopant concentrations. The excitation spectrum of Cr³⁺-doped Al₂O₃ nanopowders consist of two bands peaking at 406 nm and 570 nm and the emission spectrum consist of two bands peaking at 694 nm and 670 nm.     

Fe3+/Al3+-TiO2复合光催化剂的制备及其光催化性能研究

以钛酸四正丁酯为先驱物,采用溶胶-凝胶法制备铁铝共掺杂的TiO2(Fe3+/Al3+-TiO2)复合光催化剂,并用XRD、UV-Vis等进行表征,系统研究煅烧温度、光催化体系中的盐对Fe3+/Al3+-TiO2复合光催化剂在自然光条件下光催化降解甲基橙性能的影响。结果表明,Fe3+/Al3+-TiO2光催化降解甲基橙的性能随着煅烧温度的升高而增强,催化体系中的HCO3-和NO2-使Fe3+/Al3+-TiO2复合光催化剂的催化活性有所降低。