Properties Of Iron Aluminides Research Articles

The Effect of High-Temperature Deformation on the Structure of Iron Aluminides

The iron aluminides are very perspective materials with many advantages – for example excellent corrosion resistance and/or good strength up to 600 °C. Due to these benefits they appear as suitable materials for use in high temperature applications. But some negative properties (sharp drop in strength above 600 °C or limited ductility at room temperature) are the major obstacles for their use. One way, how to improve mechanical properties of iron aluminides, is doping of binary alloy by alloying elements, which can form strengthening precipitates. Depending on their size the precipitates of secondary phases can block dislocation movement or act as strengthening phase as known in composite materials.One from many properties, which is important to know before a new type of material is used in structural applications, is its deformation behaviour. In present paper there was studied the structure of Fe-25Al-5Zr (in at. %) sample in as cast state and in states after high-temperature deformation at 600 and 800 °C in detail. A high resolution SEM equipped with EDX and EBSD was used for the study of structure. It was measured that huge grains are presented in the structure of as cast state. After deformation at 600 °C there were still observed huge Fe3Al-matrix grains, but strongly deformed. Also formation of sub-grains due to deformation is obvious. Deformation at 800°C led to formation of small grains due to recrystallization. Higher deformation degree in non-eutectic areas led to preferential recrystallization while Fe3Al phase in eutectic regions remained deformed (nonrecrystallized).

Temperature Dependent Elastic and Ultrasonic Properties of Iron Aluminide

The anisotropic elastic constants of a B2 structured iron aluminide FeAl (Fe-40 at. % Al) alloy at different temperatures are computed using Coulomb and Born Mayer model. The temperature dependent ultrasonic properties of the alloy along with other associated parameters are determined using the elastic constants. The correlation between the mechanical and thermal properties makes ultrasonic properties a suitable, nondestructive tool to study the physical state of FeAl alloy. The results of present investigation are discussed in correlation with the microstructural phenomenon like phonon-phonon interaction and the other thermophysical properties. Temperature dependence of ultrasonic attenuation along different crystallographic directions reveals some typical characteristic features.

Electronic Structure of Bimetallic Fe<sub><i>m</i></sub>Al<sub><i>n</i></sub> (m+n=6) Clusters

Theoretical study on the electronic structure of small FemAln(m+n=6) clusters has been carried out at the BPW91 level, and the electronic structures, binding energy and vertical ionization potential of clusters were evaluated. For the stable clusters, the iron atoms gather together and form a maximum of Fe-Fe bonds, and the aluminum atoms locate around Fe core with a maximum of Fe-Al bonds. The binding energy and vertical ionization potential show that the Fe5Al, Fe4Al2 and Fe3Al3 clusters have higher stability, which results provide insight into the properties of iron-aluminides can be obtained from a finite size cluster model.

High temperature mechanical properties of iron aluminides

Considerable attention has been given to the iron aluminide family of intermetallics over the past years since they offer considerable potential as engineering materials for intermediate to high temperature applications, particularly in cases where extreme oxidation or corrosion resistance is required. Despite efforts at alloy development, however, high temperature strength remains low and creep resistance poor. Reasons for the poor high-temperature strength of iron aluminides will be discussed, based on the ordered crystal structure, the dislocation structure found in the material, and the mechanisms of dislocation pinning operating. Alternative ways of improving high temperature strength by microstructural modification and the inclusion of second phase particles will also be considered.

The strength properties of iron aluminides

For the development of Fe−Al alloys as structural materials, a deep understanding of slip and deformation properties is necessary. In particular, since mechanical properties of the iron aluminides are affected by excess vacancy strengthening as well as the positive-temperature dependence of yield stress, controlling these strength features is essential. In this article, the strength properties of iron aluminides are reviewed.

Effects of annealing temperature on the mechanical properties of an Fe-36% Al alloy

Annealing B2-ordered iron aluminides at various temperature significantly affects room temperature mechanical properties such as hardness and yield strength. This effect is caused by the retention of high concentrations of thermal vacancies during cooling. A recent study has correlated hardness changes with calculated vacancy concentrations and has concluded that vacancies cause strengthening through a point defect-dislocation interaction mechanism. The present work expands the study of the effects of annealing temperature on the mechanical properties of iron aluminides, and also includes the effects of annealing temperature on the environment-induced embrittlement of these materials. Fe-36 at.% Al specimens, after various annealing treatments, were tensile tested in oxygen and air; testing in dry oxygen results in relatively high ductilities by eliminating environmental embrittlement.

The effect of molybdenum addition on properties of iron aluminides

The effect of the addition of up to 10 pct molybdenum on several metallurgical properties of Fe-28Al (at. pct) to which 1 pct TiB2 was added for grain refinement has been studied. It was determined that the addition of molybdenum results in a decrease in grain size, an increase in the recrystallization temperature, and an increase in the DO3 to B2 ordering transformation temperature. The solubility limit of molybdenum in the matrix of the base alloy was found to be about 6 pct. At this concentration, another 1 pct is dissolved in the TiB2 precipitates. Tensile strengths were increased slightly by adding up to 2 pct Mo, but ductility decreased, even though grain sizes were reduced. The fracture mode in tension did not change with addition of molybdenum up to 2 pct.