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Lecture

Phase equilibria in the Al-Cr-Fe ternary system: experimental study and thermodynamic calculations

Thursday (27.09.2018)
10:30 - 10:45 S1/01 - A01
Part of:


The Al-Cr-Fe system is well known for lightweight aluminum alloys and oxidation resistant steels. For those application fields, accurate thermodynamic descriptions of all corresponding systems are required. For this purpose, experimental investigations in the range < 50 at.-% of aluminum were performed. They comprise the determination of order-disorder reactions and the investigation of the polythermal phase equilibrium between bcc-based alloys and γ-Al8Cr5. For the latter, four alloys were equilibrated at several temperatures and subsequently quenched in iced water. Equilibrium phase compositions were determined with EPMA/WDX method. Furthermore, the microstructure of as-cast samples were investigated and the primary solidified phase was determined with complementary methods such as ICP-OES, XRD and SEM/EDX. An additional heat effect in the ternary system between 1093°C and 1120°C, depending on the chromium content, was observed using thermal analysis (DSC 404 C). As discussed in the literature, the measured effect probably attributes to an additional Al8Cr5 modification. The course of the technological important transition reaction between disordered α-Fe,Al (A2) and ordered FeAl phase (B2) is well known for the Al-Fe subsystem. Unfortunately, only limited information are available for ternary systems. In order to describe the A2/B2 transition in the Al-Cr-Fe system, 25 alloys in the range of 5 - 25 at.-% chromium and 25 - 45 at.-% aluminum were produced. The results from thermal analysis using DSC and dilatometry indicate a continuous decrease of the A2/B2 transition temperature, by alloying chromium to the subsystem Al-Fe. The ternary interaction parameters of the B2 ordered phase were adjusted with a two sublattice order-disorder model using CALPHAD based methods. Comparison of calculated and measured transition temperatures exhibit a reasonable agreement. The obtained constitutional data from this work can be used for an improved thermodynamic modeling and optimization of the Al-Cr-Fe system.

Speaker:
Maximilian Rank
Karlsruhe Institute of Technology (KIT)
Additional Authors:
  • Dr. Peter Franke
    Karlsruhe Institute of Technology (KIT)
  • Prof. Dr. Hans Jürgen Seifert
    Karlsruhe Institute of Technology (KIT)