Browsing by Author "Schmoelzer, T"
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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.
- ItemDynamic recovery and recrystallization during hot-working in an advanced TiAl alloy(Carl Hanser Verlag, 2011-01-01) Schmoelzer, T; Liss, KD; Rester, M; Yan, K; Stark, A; Reid, M; Peel, MJ; Clemens, HIntermetallic TiAl alloys are light-weight high-temperature materials and intended to partly replace Ni based alloys in jet engines. Due to difficult forming operations, component prices are high and limit the possible field of application. During hot-working, recovery and recrystallization effects determine the microstructural evolution and thereby the mechanical properties of the finished part as well as its behavior during deformation. To study the occurring experiments with high-energy X-rays were conducted. By means of this method, the dominating processes were identified. The results were validated through electron back scatter diffraction experiments. © 2011 CARL HANSER VERLAG
- ItemIn situ characterization of a Nb and Mo containing γ-TiAl based alloy using neutron diffraction and high-temperature microscopy(Wiley-VCH Verlag Berlin, 2009-11) Watson, IJ; Liss, KD; Clemens, H; Wallgram, W; Schmoelzer, T; Hansen, TC; Reid, MIn recent times, novel titanium aluminides containing the bcc β-phase at high temperatures are being developed for improved hot-working capabilities, however, predictions of the phase diagrams are merely uncertain. Here we present in-situ neutron studies, which are particularly sensitive to the atomic disorder in the ordered phases. Complementary laser scanning confocal microscopy is employed for in-situ microstructural investigations. © 2009, Wiley-VCH Verlag Berlin
- 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.
- ItemIn situ study of dynamic recrystallization and hot deformation behavior of a multiphase titanium aluminide alloy(American Institute of Physics, 2009-12-01) Liss, KD; Schmoelzer, T; Yan, K; Reid, M; Peel, MJ; Dippenaar, RJ; Clemens, HHot-compression tests were conducted in a high-energy synchrotron x-ray beam to study in situ and in real time microstructural changes in the bulk of a beta-solidifying titanium aluminide alloy. The occupancy and spottiness of the diffraction rings have been evaluated in order to access grain growth and refinement, orientation relationships, subgrain formation, dynamic recovery, and dynamic recrystallization, as well as phase transformations. This method has been applied to an alloy consisting of two coexisting phases at high temperature and it was found that the bcc beta-phase recrystallizes dynamically, much faster than the hcp alpha-phase, which deforms predominantly through crystallographic slip underpinned by a dynamic recovery process with only a small component of dynamic recrystallization. The two phases deform to a very large extent independently from each other. The rapid recrystallization dynamics of the beta-phase combined with the easy and isotropic slip characteristics of the bcc structure explain the excellent deformation behavior of the material, while the presence of two phases effectively suppresses grain growth. © 2009, American Institute of Physics
- 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 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, HIntermetallic 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.
- 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.