Browsing by Author "Zickler, GA"

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    In and ex situ investigations of the β-phase in a Nb and Mo containing gamma-TiAl based alloy.
    (Elsevier, 2008-06) Clemens, H; Chladil, HF; Wallgram, W; Zickler, GA; Gerling, R; Liss, KD; Kremmer, S; Guther, V; Smarsly, W
    In β-stabilized Ti-43Al-4Nb-1Mo-0.1B alloy (composition in atomic percent) the correlation between the occurrence of β-phase and temperature was analyzed experimentally and compared to thermodynamic calculations. Results from in situ high-energy X-ray diffraction, texture measurements, heat treatments, scanning electron microscopy, and temperature-dependent flow stress measurements were used to study the evolution of the β-phase with temperature. Thermodynamic calculations based on the CALPHAD method were applied to correlate the phases developed in the β-solidifying TiAl based alloy under investigation. This alloy is characterized by an adjustable β-phase volume fraction at temperatures where hot-work processes such as forging and rolling are conducted. Due to a high volume fraction of β-phase at elevated temperatures the hot-extruded alloy can be forged under near conventional conditions. © 2008, Elsevier Ltd.
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    Phase fractions, transition and ordering temperatures in TiAl-Nb-Mo alloys: an in- and ex-situ study.
    (Elsevier, 2010-08) Schmoelzer, T; Liss, KD; Zickler, GA; Watson, IJ; Droessler, LM; Wallgram, W; Buslaps, T; Studer, AJ; Clemens, H
    Intermetallic γ-TiAl based alloys of the TNM™ alloy family attain their excellent processing characteristics by a high β-phase content present at hot-working temperatures. Subsequent to hot-working the β-phase content is decreased by a heat treatment step performed at temperatures where the β-phase fraction exhibits a minimum. In this study, in- and ex-situ experiments were conducted on three alloys with different contents of β/β0 stabilizing elements. The course of phase fractions as a function of temperature as well as phase transition temperatures were determined by means of in-situ high-energy X-ray diffraction experiments. Additionally, dynamic scanning calorimetry investigations were performed to obtain complementary data on the transition temperatures. Quantitative metallography was conducted on heat treated and quenched specimens to acquire additional information on the dependence of the phase fractions on temperature. By neutron diffraction experiments the ordering temperatures of the constituent phases were determined. It was shown that the experiments yielded consistent results which differ significantly from ThermoCalc simulations for which a commercial TiAl database was used. The differences between the experimental results and the thermodynamic predictions are discussed. © 2010, Elsevier Ltd.
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    Phase transition and ordering temperatures of TiAl-Mo alloys investigated by in-situ diffraction experiments
    (Trans Tech Publications, 2010-08-02) Schmoelzer, T; Mayer, S; Haupt, F; Zickler, GA; Sailer, C; Lottermoser, L; Guther, V; Liss, KD; Clemens, H
    Intermetallic TiAl alloys with a significant volume fraction of the body-centered cubic β-phase at elevated temperatures have proven to exhibit good processing characteristics during hot-working. Being a strong β stabilizer, Mo has gained importance as an alloying element for so-called β/γ-TiAl alloys. Unfortunately, the effect of Mo on the appearing phases and their temperature dependence is not well known. In this work, two sections of the Ti-Al-Mo ternary phase diagram derived from experimental data are shown. These diagrams are compared with the results of in-situ high-temperature diffraction experiments using high-energy synchrotron radiation. © 2020 by Trans Tech Publications Ltd.