Investigation of phase equilibria in the Al–Cr–Fe system in a region with a high aluminum content (more than 50 at.% ) is important for the development of new heat-resistant and corrosion-resistant alloys. Aluminum, chromium, and iron are common elements, and their combinations can lead to the formation of complex phase structures that determine the properties of alloys.
This paper presents the results of experimental studies of isothermal cross sections of the Al–Cr–Fe phase diagram at various temperatures in the range from 800 °C to 1200 °C. Differential thermal analysis (DTA), X-ray phase analysis (XRD), and microscopic analysis were used to determine the phase composition and microstructure of alloys.
It is established that several solid phases exist in the studied concentration range, including aluminum-based solid solution (Al), intermetallic compounds AlxCryFez (where x, y, and z are stoichiometric coefficients), and iron – based solid solution (Fe). The equilibrium phase regions and phase compositions are determined for each temperature.
In the temperature range from 700 to 1160 °C (namely, at 1160, 1100, 1075, 1042, 1000, 900, 800 and 700 °C), the percentage of Al and individual isothermal cross sections were determined. The Al–Cr–Fe diagram was studied for compositions in the range of 50-100%. In the region of compositions with a low aluminum content, the isostructural high-temperature y1 phases of the Al–Cr and Al–Fe systems form a continuous zone of solid solutions.
It was found that the binary compounds Al13Fe4 and Al5Fe2 can dissolve up to 6.5 at% Cr, while Al2Fe can dissolve up to 4.1 at% Cr. It was found that solid solutions of the γ2 and μ phases based on Al-Cr contain 35.2 and 1.3 at% Fe, respectively. The effect of Cr dissolution in binary Al–Fe alloys on the Al concentration is insignificant, while in binary Al–Cr alloys the Al concentration decreases with increasing Fe concentration.
In the n-phase, Al-Cr is dissolved to 5 at% Fe, which causes a significant drop in the Al concentration and an increase in the melting point. The presence of the triple decagonal phase D3 and the three complex periodic phases O1, H, and ε previously detected was confirmed, and their compositions at different temperatures were refined.
Analysis of the experimental data allowed us to construct isothermal cross-sections of the Al-Cr-Fe phase diagram. The results obtained indicate a complex phase structure of the system and a strong influence of temperature on phase equilibria. As the temperature increases, the region of the aluminum-based solid solution expands and the stability of intermetallic compounds changes.
The obtained data can be used to optimize the composition and heat treatment of aluminum alloys containing chromium and iron in order to improve their mechanical properties and corrosion resistance.
Author: D. Pavlyuchkov, B. Przepiórzyński, W. Kowalski, T.Ya. Velikanova, B. Grushko
The Institute: Frantsevich Institute of Materials Science Problems, Department of Physical Chemistry of Inorganic Materials, 03680 Kiev, 142, Ukraine, Technical University of Freiberg, Institute of Materials Science, D-09599 Freiberg, Germany, IFF3, Jülich Research Center, D-52425 Jülich, Germany, Institute of Materials Science, Silesian University, 40007 Katowice, Poland