Sintered soft magnetic Fe-Al,Fe-Si,and Fe-Si-Al alloys

Summary The results are presented of an investigation of soft magnetic iron-aluminum, iron-silicon, and iron-silicon-aluminum alloys produced by powder metallurgy methods. A study was made of the effect of preparation conditions on the magnetic and electrical properties of these alloys. It was found that powder metallurgy permits the preparation of one-piece magnetic cores which in many cases can be used in 50 cps alternating fields.     

Nitrogenation of Fe-Al alloys. III: Absorption of hydrogen in nitrogenated Fe-Al alloys

Nitrogenation of Fe-2 pct Al alloys produces a large number of A1N particles and a large density of dislocations in the ferrite. We have measured the amount of nitrogen absorbed reversibly as a function of nitrogen activity at 500°C by alloys nitrogenated under different conditions. We have also measured the reversible hydrogen absorption at room temperature as a function of hydrogen fugacity and with varying amounts of preadsorbed nitrogen. Some preparative treatments produce some AIN-ferrite interface that can reversibly adsorb nitrogen at 500°C and hydrogen at 24.5°C upon sites not occupied by nitrogen. In the absence of such interface, the nitrogen absorption isotherms and the nitrogen-free hydrogen absorption isotherms are adequately described by a model based upon the thermodynamics of stressed bodies. However, the observed decrease of absorbed hydrogen caused by preabsorbed nitrogen is not explicable by the simple idea that a site occupied by nitrogen is unavailable to hydrogen.     

Sintered metals and alloys

The paper examines the production of a composite material that is double hardened by adding titanium carbides and borides to the steel and by quenching the metal matrix and letting it to age. Samples containing 30 wt.% TiC or TiB₂ are produced by liquid phase sintering, hot pressing, and hot forging. The effect of thermal treatment on the mechanical properties and structural state of the material is investigated. The material quenched and aged is established to be twice as durable and hard as the sintered one. Hence, it can be mechanically treated after sintering and then thermally treated. The highest possible strength of the material produced is 1400 to 1500 MPa and hardness 60 to 65 HRC. Strengthening worn reinforcing-wire knives with plates of the composite material prolonged their life by 50 to 100% compared with the standard knife. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 7–8 (456), pp. 28–34, 2007.     

Phase relationships in the iron-rich Fe-Al alloys

X-ray diffraction study of isothermally annealed powder specimens of Fe-Al alloys with 18.75 to 32 at. pct Al indicates that the α + FeAl two-phase field closes at around 662‡C where both phases have the same composition: 23.9 at. pct Al. X-ray diffraction and magnetic data show that any twophase field that may exist between the FeAl and Fe₃Al phases must be extremely narrow. It is probable that there is no two-phase field and that the transition is of a higher than first order type.     

Sintered magnesium and magnesium-beryllium alloys

Summary The use of powder metallurgy methods for the production of magnesium alloys is highly promising. By employing technological procedures widely known in powder metallurgy practice, it is possible to make magnesium alloys whose production by the methods of melting and casting would be hardly feasible.The addition of finely dispersed magnesium oxide and an excess beryllium phase to the magnesium matrix secures an excellent combination of long-time oxidation and heat resistance at temperatures substantially above the permissible operating temperatures of the usual magnesium-base alloys.     

The electron metallography of ordering reactions in Fe-Al alloys

The microstructural changes during the α→ FeAl, FeAl → Fe₃Al, and α→ Fe₃Al transitions were studied by transmission electron microscopy. The ordering of ferromagnetic α was observed to occur in a classical manner by the nucleation and growth of particles of the FeAl or Fe₃Al type phases. However, the ordering of paramagnetic α to FeAl and paramagnetic FeAl to Fe₃Al occurred by a mechanism which showed many of the characteristics expected of a second or higher degree transition. These included critical point fluctuations in the degree of long-range order which also appeared to be greater in the vicinity of antiphase domain boundaries. The FeAl phase was also observed to partially disorder in the initial stages of the FeAl → α + FeAl transition and this effect appears to account for the anomalous magnetic behavior of some FeAl alloys.     

Crystallographic textures in rolled and annealed Fe-Ga and Fe-Al alloys

The feasibility of obtaining [001] preferred texture in polycrystalline Fe₈₅Ga₁₅ and Fe₈₅Al₁₅ magnetostrictive alloys containing 1 mol pct NbC using a low-cost conventional thermomechanical processing approach is shown in this work. Thermomechanical processing conditions examined consisted of a sequence of hot rolling, two-stage warm rolling at 400 °C with intermediate anneal at 900 °C and texture anneal in the temperature range of 900 °C to 1300 °C for time periods up to 24 hours. Textures present prior to and after texture annealing were characterized using orientation imaging microscopy in a scanning electron microscope. In the case of Fe₈₅Ga₁₅ alloy with 1 mol pct NbC, the deformation-induced texture after a two-stage warm rolling consists of mixed {100} 〈110〉 and {111} 〈110〉 type partial textures. Texture annealing of the Fe₈₅Ga₁₅ alloy with 1 mol pct NbC at 1150 °C for 2 hours changes the texture to a predominant texture that is close to {001}〈100〉. On increasing the annealing time to 24 hours, the texture shifts toward {110}〈100〉. While texture anneal at both 1150 °C and 1300 °C produces a [001] or near-[001] preferred orientation along the rolling direction in the Fe₈₅Ga₁₅ alloy with 1 mol pct NbC, 1150 °C-24 hour treatment was found to provide the strongest [001] orientation among the conditions examined. Similar trends are observed for the case of Fe₈₅Al₁₅ alloy with 1 mol pct NbC.     

Fe-Al和Fe-Cr-Al合金在高温下的初期氧化

研究了Fe-10Al、Fe-5Cr-10Al和Fe-10Cr-10Al分别在900℃和1 000℃的初期氧化行为.利用电子显微镜(SEM)和俄歇电子谱(AES)分析了合金表面形成氧化膜的形貌与组成.Fe-Cr-Al实现铝的选择性氧化所需的时间取决于合金中铝和铬的质量分数,同时也与氧化温度有关,较高的反应温度能促进铝的选择性氧化.Fe-10Cr-10Al比Fe-5Cr-10Al更快地实现铝的选择性氧化,而Fe-5Cr-10Al在1 000℃比在900℃更快实现铝的选择性氧化.     

Thermoelectric properties of the Fe-Al and Fe-Al-Si alloys for thermoelectric generation utilising low-temperature heat sources

The iron is intrinsically a p-type conductor. When aluminum with three valence electrons is added to the iron, the d-subbands are occupied by electrons, so alloying with the aluminum transforms the iron to the n-type conductor, hence the p-n junction is made possible. Furthermore, when silicon is added to the n-type Fe-Al alloy, this alloy returns to the p-type conductor. Therefore, the thermoelectric p-n junctions with high thermoelectric power have been recognised (figures in % refer to mass contents): Fe(p) – Fe12%Al(n): α=38μV/K and Fe12%Al12%Si(p) – Fe12%/Al(n): Δα=70μV/K. Thermoelectric generation offers the possibility of a gigantic electric power generation utilising low-temperature sources of energy below 700 K such as exhaust heat from the central-station steam-electric plant, solar heat and terrestrial heat. The immense production of electricity by this principle is made possible exclusively by means of the conversion materials consisiting of the iron and iron-based alloy because the generator can be manufactured on an efficient mass production basis, and the alloys mentioned above will meet this requirement. In this paper, the thermoelectric properties of these alloys such as Seebeck coefficient, thermal conductivity and electrical resistivity were experimentally determined in the temperature range between 300 and 700 K to provide basic data on the conversion materials with respect to the thermoelectric generation utilising low-temperature heat sources.     

Activities in carbon-saturated Fe-Al alloys and the stability of Al4C3 at 1873 K

The Knudsen cell-mass spectrometer combination has been used to study carbon-saturated Fe-Al alloys at 1873 K. Activities are derived and presented for both metallic components as a function of the composition variableN _Al/(N _Al + N _Fe ).From the composition for the separation of the carbide, the standard Gibbs Energy of formation of Al₄C₃ is determined to be -88.8 ± 11.2 kJ mole^-1 at 1873 K. Formerly a Graduate Student.     

Activities in carbon-saturated Fe-Al alloys and the stability of Al4C3 at 1873 K

The Knudsen cell-mass spectrometer combination has been used to study carbon-saturated Fe-AI alloys at 1873 K. Activities are derived and presented for both metallic components as a function of the composition variableN _Al/(N_A + N_Fe). From the composition for the separation of the carbide, the standard Gibbs Energy of formation of A1₄C₃ is determined to be -88.8 ± 11.2 kJ mole⁻¹ at 1873 K. Dr. Choudary was formerly a Graduate Student.