Browsing by Author "Mayer, S"
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- ItemThe contribution of high-energy x-rays and neutrons to characterization and development of intermetallic titanium aluminides(Wiley-Blackwell, 2011-08-01) Schmoelzer, T; Liss, KD; Staron, P; Mayer, S; Clemens, HAbstract Intermetallic γ-TiAl based alloys are a novel class of lightweight structural materials that exhibit excellent high-temperature strength while having low density. These properties make them ideal candidates for replacing dense Ni base alloys currently used in the temperature range from 550 to 750 °C. Therefore, extensive research activities were conducted during the last 20 years to make this innovative class of materials fit for service. In this task, diffraction methods have been an important tool for promoting the development of TiAl alloys. The ability to perform experiments in situ and to determine phase fractions even in cases where two phases are present in ultrafine lamellar structures are only two examples for applications in which diffraction methods are indispensable. In this work, a review is given concerning the use of diffraction methods in the development of TiAl alloys. Different methods are introduced and highlighted by examples. This review lists the advantages of diffraction experiments and critically discusses the limits of the individual methods.© 2011, Wiley-Blackwell.
- ItemIn situ diffraction experiments for the investigation of phase fractions and ordering temperatures in Ti-44 at% Al-(3-7) at% mo alloys(Wiley, 2011-04-01) Schmoelzer, T; Mayer, S; Sailer, C; Haupt, F; Guther, V; Staron, P; Liss, KD; Clemens, HBeing a strong beta stabilizer, Mo has gained importance as an alloying element for so-called beta/gamma-TiAl alloys. Intermetallic TiAl-based alloys which contain a significant volume fraction of the body-centered cubic beta-phase at elevated temperatures have proven to exhibit good processing characteristics during hot-working. Unfortunately, the effect of Mo on the appearing phases and their temperature dependence is not well known. In this work, sections of the Ti-Al-Mo ternary phase diagram derived from thermodynamic calculations as well as experimental data are presented. The phase transition temperatures stated in these phase diagrams are compared with the results of high-temperature diffraction studies using high-energy synchrotron radiation. Additionally, the disordering temperature of the beta(o)-phase is determined. © 1999-2020 John Wiley & Sons, Inc.
- ItemAn in-situ high-energy X-ray diffraction study on the hot-deformation behavior of a β-phase containing TiAl alloy(Elsevier Science Ltd., 2013-08-01) Schmoelzer, T; Liss, KD; Kirchlechner, C; Mayer, S; Stark, A; Peel, MJ; Clemens, HIn engineering materials, microstructural evolution during hot-working critically determines the properties of the finished part. Intermetallic TiAl alloys are no exception and numerous attempts have been made to improve their performance by subjecting them to harmonized hot-working steps. In the current work a novel in-situ diffraction technique along with conventional microscopic methods were employed to characterize the behavior of the individual phases at two different deformation temperatures. A so-called TNM™ alloy with a nominal composition of Ti-43.5 Al-4 Nb-1 Mo-0.1 B (in at%), which exhibits an adjustable fraction of disordered β-phase at elevated temperatures, was deformed isothermally at 1220 °C and 1300 °C. At 1220 °C three phases (α,β,γ) are present in thermodynamic equilibrium which reduces to two (α,β) at 1300 °C. It was possible to observe in-situ the individual behavior of the involved phases during deformation and the phenomena which accommodate the defects generated by hot-working. Results of post-mortem microscopic investigations were used to confirm the findings. The results of the in-situ experiments give unique insights into the hot-deformation behavior of multi-phase TiAl alloys, which can be used for specific process optimization and for further alloy development. © 2013, Elsevier Ltd.
- ItemPhase transition and ordering behavior of ternary Ti-Al-Mo alloys using in-situ neutron diffraction(HANSER eLibrary, 2011-06-01) Kabra, S; Yan, K; Mayer, S; Schmoelzer, T; Reid, M; Dippenaar, RJ; Clemens, H; Liss, KDNeutron diffraction has been used for in-situ. investigations to elucidate the phase transformation behavior of two Mo-containing TiAl alloys with compositions of Ti-44Al-3Mo and Ti-44Al-7Mo (in at.%). Five different phases are present in these alloys. These include three ordered phases at room temperature, namely alpha(2), beta(0) and gamma and two disordered phases, alpha and beta, which occur at higher temperatures. The sequence of the three phase transformations in each alloy has been determined. The phase transformation and disordering/ordering temperatures were determined on heating and cooling from the diffracted peak intensities. The neutron experiments are particularly sensitive to the order disorder transitions in TiAl alloys, which are compared with the overall phase fractions obtained from previous high energy X-ray diffraction. Hysteresis and undercooling effects are observed for the various phase transformations and depend on the nature of atomic rearrangements. © 2011 Carl Hanser Verlag GmbH & Co. KG
- ItemPhase 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, HIntermetallic 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.