A study on the preparation of iron aluminium based intermetallic alloy by aluminothermic smelting technique

Iron aluminium based intermetallic alloys or iron aluminide alloys are usually made by conventional melting and powder processing routes. Melting is carried out either in vacuum induction melting or arc melting furnaces. However,the use of high vacuum and high temperature expensive furnaces, high cost associated with the procurement of pure individual metal components, operational problems during melting stages are some of the most deterrent factors in making these alloys by melting route. Powder processing route utilises atomised, carbonyl or rapidly solidified pre alloyed powders as starting materials and alloying is carried out either by mechanical alloying or reaction synthesis or by consolidation through hot isostatic pressing. This process also involves many processing steps and considerable expense. In the present investigation, it has been found possible to eliminate the above problems by adopting a simple aluminothermic reduction (thermit) smelting technique for the preparation of iron aluminide alloy of targetted composition Fe–16Al–5.46Cr–0.5V–0.05C (wt %) by the direct co-reduction of oxides of iron,chromium and vanadium in presence of carbon and excess aluminium. Incorporation of slag fluidizer CaO amounting to 10 wt % of total charge, aluminium, 10 wt % excess over stoichiometric requirement and carbon, double the theoretical amount have been found to be adequate to form the above alloy with maximum overall yield of 99.4 wt %. The compositional variation of alloying components like iron, chromium,vanadium, aluminium and carbon in the aluminothermically produced iron aluminide alloy from the target composition have been minimized under optimum experimental conditions. The reactions have been found to be well controlled, rapid and self-sustaining and are conducted in an off-furnace manner using a simple experimental set-up.Studies on composition and microstructure characterization, hot rolling behaviour and oxidation resistance of the said alloy points towards its suitability for use.     

Fabrication of Ti-Al intermetallics by a two-stage aluminothermic reduction process using Na2TiF6

A novel two-stage method, based on aluminothermic reduction of Na₂TiF₆, has been proposed to prepare Ti-Al intermetallic alloys in this paper. The entire process of the two-stage aluminothermic reduction was introduced in detail. The result of thermal analysis demonstrated that the aluminothermic reduction reaction was an exothermic process and occurred at approximately 660 °C. Besides Ti-containing cryolite, pure Ti₃Al, TiAl and TiAl₃ intermetallics could be prepared after the first stage reduction. Further, in secondary reduction, Ti-containing cryolite contained Ti⁴⁺, TiOS and Ti-Al intermetallics could be purified completely. As a result, pure cryolite and Al-Ti alloy were obtained. A concept of continuous and cyclic route was proposed. The two-stage aluminothermic reduction process provided a high productivity and pollution-free metallurgical way for preparing Ti-Al intermetallic alloys.     

Studies on the development of TZM alloy by aluminothermic coreduction process and formation of protective coating over the alloy by plasma spray technique

TZM alloy is a potential candidate for high temperature structural applications. However, in the preparation of this alloy by conventional melt-casting route, difficulties are encountered in achieving homogenized alloy composition in view of high melting temperature of the alloy and presence of minor alloying components. Therefore, an alternative technique of aluminothermic co-reduction was adopted to prepare TZM alloy of composition, Mo-0.5Ti-0.1Zr-0.02 °C, wt.% by simultaneous reduction of uniformly premixed oxides of MoO₂, TiO₂ and ZrO2 by aluminium in presence of requisite amount of carbon. The as-reduced alloy was further arc melted for consolidation. Since, TZM alloy is by nature highly susceptible to oxidation at elevated temperature in air or oxygen, therefore feasibility of development of silicide type of coating over the synthesized alloy by plasma coating technique was also examined. Silicon powder coated on TZM alloy surface by plasma spray technique was finally converted into MoSi₂ coating by sintering at 1350 ^°C for 2-4 h duration under argon. A double layer coating structure was formed with two distinct phases. The inner thin layer was consisted of Mo₂Si₅ phase (~ 10 μm) followed by thick outer layer of MoSi₂ (~ 150 μm). The coating showed good adhesion strength and stable oxidation with negligible mass gain (10 g/m²) at 1000 ^°C in air.     

Preparation of primary Al-Si alloy from bauxite tailings by carbothermal reduction process

Effects of various reaction parameters such as atmospheric pressure, treating temperature, sintering time and bituminite content on the preparation of primary Al-Si alloy by carbothermal reduction of bauxite tailings were investigated by XRD,XRF, infrared absorption carbon-sulfur analysis unit and SEM coupled with EDS. Meanwhile, the mechanism of carbothermal reduction of Al2O3 and SiO2 was discussed. It is found that pressure and temperature are major factors that influence the carbothermal reduction of bauxite tailings. The appropriate conditions for preparation of primary Al-Si alloy are as follows: atmospheric pressure of 0.1 MPa, heating temperature of 1 900 ℃,bituminite content of 95% (mass fraction) of theoretic bituminite content and sintering time of 1 h. Among four mechanisms of carbothermal reduction of Al2O3 and SiO2, the theory of the formation and decomposition of carbides might be the best one to interpret the reaction process.     

Effects of the Zr and Mo contents on the electrochemical corrosion behavior of Ti–22Nb alloy

Ti–22Nb–xZr and Ti–22Nb–xMo (x = 0, 2, 4, 6, in atom percent) were prepared by an arc melting method. The alloys were solution‐treated at 1073 K for 1.8 ks followed by quenching them into ice water, and the electrochemical corrosion behavior in a 0.9% NaCl solution at 25 °C and neutral pH range of the solution‐treated alloys was evaluated by using electrochemical impedance spectroscopy, polarization curves and an equivalent circuit analysis. It was found that the microstructure of the solution‐treated Ti–22Nb alloy mainly contains β phase with small amount of α″ phase, and the addition of Zr or Mo to a Ti–22Nb alloy is efficient to stabilize the β phase. The resulting impedance parameters and passive current densities indicated that the corrosion resistance of the Ti–22Nb alloy was promoted significantly with the addition of Zr and Mo.     

Ageing behavior of Cu-15Ni-8Sn alloy prepared by mechanical alloying

1INTRODUCTIONCu-Ni-Snal1oyshavebeenconsideredaspossiblesubstitutesforCu-Bealloysinthemanu-factureofc0nnectors,springcomponentsandsoforth,intheelectronicsindustriesbecauseoftheiroutstandingpropertiessuchashighstrength,highelasticmodulus,exce1lenterosi0nresistanceandhighresistancetostressrelaxationatelevatedtemperature['].Inaddition,com-paredwithCu'Bealloys,thelowcostandminorpollutioninthepreparationprocessofthealloyhavealsoattractedtheincreasingattentionofmanyresearchers.However,extensiv…     

时效对铸造Cu-15Ni-8Sn合金组织与性能的影响

对铸造Cu-15Ni-8Sn合金进行均匀化处理和固溶处理后,研究了时效温度和时效时间对合金硬度和导电率的影响。通过对显微组织以及硬度和导电率的变化分析结果表明,时效时间和时效温度对Cu-15Ni-8Sn合金的硬度和导电率都有较大影响,并确定了Cu-15Ni-8Sn合金最佳时效时间是5 h,最佳时效温度是425 ℃。     

铝热还原工艺条件对Al-Ti-Ce中间合金物相结构和合金元素浓度的影响

在Na3AlF6-NaCl-KCl氟氯混合电解质体系中,通过铝热还原法以TiO2和CeO2为Ti源和Ce源,制备Al-Ti-Ce中间合金。研究反应时间、反应温度、电解质构成（Na3AlF6质量百分含量）、K2TiF6添加量四种工艺条件对Al-Ti-Ce中间合金物相结构和合金元素浓度的影响。实验结果表明,在所有实验工艺参数范围内,制备的Al-Ti-Ce中间合金均由ɑ-Al、Al3Ti和Ti2Al20Ce三相构成。制备的最佳单因素工艺参数为：反应时间90 min,反应温度850℃,Na3AlF6质量百分含量40 %、K2TiF6添加量20 mol%。热力学分析结果从理论上进一步证明了在实验条件下几种主要化学反应的可行性。     

铝热还原酸溶性钛渣制备TiAl基多元合金

对含高钛的酸溶性钛渣进行铝热还原制备钛铝基多元合金。为了控制并了解合金的制备,讨论了铝和氧化钙的添加和温度的影响。通过考虑材料的配比计算,可以成功地使合金与渣合金分离。大多数还原元素的回收率表现为高值,在所有实验条件下均为95%。铝的添加主要影响合金的成分,而氧化钙的添加则通过改变渣系成分来影响渣金分离。此外,系统的温度可以提高大部分还原元素的回收率和分配比。     

Synthesis of Al2O3／WC powder by aluminothermic reduction and carbonization method

Al2O3/WC powder was synthesized by means of aluminothermic reduction-carbonization with metallic Al powder, yellow tungsten oxide and carbon black or graphite as raw materials under the protection of coke granules.The effects of Al2O3 content, temperature, C/WO3 molar ratio, and atmosphere on the synthesis of Al2O3/WC powder were studied. The results show that the relative content of WC and W2C is strongly influenced by the factors mentioned-above. Carbon black has higher reactivity than graphite. Al2O3-WC composite is easier to obtain under the protection of coke granules than under argon atmosphere. The CO in the coke layer can easily react witht ungsten to form WC and to transfer from W2C to WC.     

以白云石和菱镁石的混合物为原料真空铝热还原法炼镁过程的动力学（英文）

研究真空铝热还原煅烧白云石和煅烧菱镁石的混合物炼镁过程的动力学,提出一种满足真空铝热过程的等温还原方法。实验在4 Pa的真空下进行。实验结果表明:还原率随着温度、制团压力和铝粉添加量的提高而增加。对不同还原时间的还原渣进行XRD分析,结果表明,还原过程能够粗略地分为3个阶段:MgAl2O4和Ca12Al14O33的形成阶段;CaAl2O4的生成阶段;CaAl4O7的形成阶段。根据动力学模型将获得的实验数据分为3部分,这3部分的活化能分别为98.2、133.0和223.3 kJ/mol。     

以白云石和菱镁石的混合物为原料真空铝热还原法炼镁的机理(英文)

利用SEM和EDS研究真空铝热还原煅白和煅烧菱镁石的混合物炼镁的反应机理。结果表明,根据在温度T时,t时间的还原率ηt与此温度下实验最终获得的还原率ηf的比,将还原过程分为三个阶段:0≤ηt/ηf≤0.43±0.06、0.43±0.06≤ηt/ηf≤0.9±0.02、0.9±0.02≤ηt/ηf<1。第一阶段为铝分别与煅烧菱镁石和煅白反应,主要产物为12CaO·7Al2O3和MgO·Al2O3,还原速率受化学反应的控制;Ca2+伴随熔融铝的扩散和化学反应速度决定了第二阶段的还原速率,CA相是此阶段的主要产物;CA2相在第三阶段产生,反应速率受Ca2+扩散控制。     

Preparation of ferromagnetic binary alloy fine fibers by organic gel-thermal reduction process

Ferromagnetic metal fibers with a high aspect ratio （length/diameter） are attractive for use as high performance electromagnetic interference shielding materials. Ferromagnetic binary alloy fine fibers of iron-nickel, iron-cobalt and cobalt-nickel were prepared by the organic gel-thermal reduction process from the raw materials of critic acid and metal salts. These alloy fibers synthesized were featured with a diameter of about 1 pm and a length as long as 1 m. The structure, thermal decomposition process and morphologies of the gel precursors and fibers derived from thermal reduction of the gel precursors were characterized by FTIR, XRD, TG/DSC and SEM. The gel spinnability largely depends on the molecular structure of metal- carboxylates formed during the gel formation. The gel consisting of linear-type structural molecules shows good spinnability.     

真空碳热还原制备Mg-Li合金热力学分析

提出了真空碳热还原制备Mg-Li合金的新思路,并对还原反应进行了热力学分析,研究了还原反应的反应式、吉布斯自由能及临界还原温度。结果表明:真空碳热还原制备Mg-Li合金具备热力学可行性,且其吉布斯自由能随真空度和反应温度的升高而降低;相同真空度下,该反应的临界反应温度低于真空碳热还原制备金属Mg、金属Li的临界温度,反应更容易进行;当真空度为10 Pa,Li_2O的相对比例为0.1时,真空碳热还原制备Mg-Li合金的临界反应温度为1345 K;在常规皮江法(真空硅热还原法)制镁的反应条件下,不论反应物料中Mg O、Li_2O相对比例为多少,真空碳热还原制备Mg-Li合金均具有热力学可行性。     

Quantitative analysis of phases formed in the aluminothermic reduction of Ta2O5 by plasma

A novel technique of aluminothermic reduction of tantalum oxide is developed to produce tantalum in form of powder. In this technique, hydrogen plasma is used to trigger the reaction in a plasma reactor. The reacted powders were analyzed by XRD and SEM. Rietveld method was used to quantify the phases present in the product of reaction. The results showed that a tantalum rich phase with a dendritic structure, typical of molten phases is formed. This phase occurred in significant amounts onto the surface and in bulk of the reacted grains.     

Nb–20%Ta alloy powder by the hydriding–dehydriding technique

Nb–Ta alloys have been used in the chemical industry to substitute pure Ta in corrosive environments (inorganic acids at high temperature). The production of components from these alloys does not show important technical problems due to the high ductility of these materials. The present work is aimed at the production of Nb–20%Ta (wt%) alloy powders by the hydriding–dehydriding technique. The alloy was produced in ingot form by the aluminothermic reduction of oxides (Nb₂O₅/Ta₂O₅) and electron beam melting. The hydriding step has been carried out in a hydrogen gas atmosphere at different temperatures using chips machined from the ingot. No significant hydriding has been observed in the experiments carried out below 500 °C, meaning that it is the lowest possible hydriding temperature of the material through the adopted experimental procedure. The XRD patterns of the hydride and Nb–20%Ta powders coincide with those of β-NbH_0.89 and Nb XRD standards, respectively. The powders were of angular and irregular morphology. The specific masses of the hydride and Nb–20%Ta powder were determined as approximately 8.55 and 9.57 g/cm³, respectively. The apparent and TAP specific masses of the hydride and Nb–20%Ta powders were (4.30/5.60) and (4.65/6.10) g/cm³, respectively.     

金属热还原法制备V-Ti-Fe中间合金(英文)

采用金属热还原热法制备V-Ti-Fe中间合金,考察V2O5与TiO2的加入比例、用铝量和Al-Mg合金用量对金属回收率和合金成分的影响。结果表明:最佳工艺参数为原料中V2O5和TiO2的质量比为0.5:1,实际用铝量为理论值的95%,Al-Mg合金用量为铝量的1/3。能谱分析结果表明,合金中的V和Fe元素分布比较均匀,Ti则存在一定偏析。为降低合金中Al和O的杂质含量,进行喷吹造渣精炼。精炼后,合金中的铝含量由4.27%降为1.86%,氧含量由2.10%降为0.91%。     

Recycling high density tungsten alloy powder by oxidization—reduction process

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真空硅热同步还原制备镁锰研究

阐述锰在镁合金中的作用以及镁锰合金的性能、应用与制备.为了提高镁锰合金中的含锰量,制备新型镁合金及南含锰量Mg - Mn中间合金,分析富锰渣硅热还原的基本原理,提出真空硅热还原制备镁锰合金的新方法.通过热力学分析真空硅热同步还原MgO、MnO,其平衡蒸汽压关系是:Mn的平衡蒸汽压＞Mg的平衡蒸汽压＞系统压强;同步还原条件是:P系≤102 Pa,T还≥1517K;还原温度为1550K时,同步固化冷凝温度T＜922K.研究设计了真空熔融及热还原设备用于实验研究真空硅热同步还原制备镁锰.