Freiberg, Germany
Freiberg, Germany

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Schmoelzer T.,University of Leoben | Mayer S.,University of Leoben | Sailer C.,University of Leoben | Haupt F.,GfE Fremat GmbH | And 4 more authors.
Advanced Engineering Materials | Year: 2011

Being a strong β stabilizer, Mo has gained importance as an alloying element for so-called β/γ-TiAl alloys. Intermetallic TiAl-based alloys which contain a significant volume fraction of the body-centered cubic β-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 βo-phase is determined. Intermetallic TiAl alloys with high contents of disordered body-centered cubic β-phase are known to exhibit good processing characteristics during hot-working. Mo is one of the elements used for stabilizing this phase but has an otherwise not very well investigated influence on the phase equilibria. To shed light on the effect of Mo on the phase diagram, two model alloys with different Mo contents were produced and investigated by microscopic and diffraction techniques. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA.


Grant
Agency: Cordis | Branch: FP7 | Program: JTI-CS | Phase: JTI-CS-2010-4-SAGE-04-004 | Award Amount: 550.00K | Year: 2011

The major requirement on gamma-TiAl feedstock materials for subsequent forging operations (forging stocks) is a fine grained microstructure which decreases the flow stresses at elevated temperatures. Novel gamma-TiAl based TNM alloys have been developed from a consortium consisting of GfE, Bhler, MTU and University of Leoben in order to increase wrought processing capability by the addition of the bcc structured beta-Ti phase into the well known alpha2/gamma microstructure of Titanium Aluminides. As a side effect, the microstructure remains fine grained due to a different solidification path of the alloy which is characterized by a complete beta-solidification mechanism. It has been demonstrated that the as-cast TNM alloy can be subsequent wrought processed without primary ingot conversion via extrusion technology. Thus, the objective of the materials conversion technology is reduced to the generation of small size parts. There is a substantial interest in improved homogeneity, high reproducibility and low overall production costs including ingot manufacturing and ingot conversion. In the project, different materials production technologies such as VAR and PAM are being evaluated. The conversion of the resulting ingots to small size forging stocks will be performed via VAR skull melting and VIM skull melting, both followed by casting in permanent moulds, HIP and machining. The objective of the project is the development of a low cost casting process for gamma-TiAl based TNM alloys which guarantees to meet all technical specifications of the products.


Bolz S.,TU Brandenburg | Oehring M.,Helmholtz Center Geesthacht | Lindemann J.,GfE Fremat GmbH | Pyczak F.,TU Brandenburg | And 8 more authors.
Intermetallics | Year: 2015

In the cast condition γ titanium aluminide alloys that solidify completely through the β phase are characterized by fine and homogeneous microstructures, weak textures and low segregation. For these reasons such alloys have a relatively good workability and can be closed-die forged without preceding ingot breakdown even if the alloys contain no large fractions of the β phase at the working temperature. The present work was devoted to a combined study of the constitution and microstructural morphologies that develop in various two-step heat treatments of a single-step forged β solidifying alloy. The study included high-energy X-ray diffraction for in situ investigations of the constitution at the heat treatment temperature. It was observed that the phase transformations are quite sluggish in the material which results in fine microstructures and some conditions that significantly deviate from thermodynamic equilibrium. Further, tensile and creep testing was carried out on the different material conditions in order to identify the range in which the properties can be varied. It is found that this easily forgeable material exhibits comparable strength, ductility and creep strength as more conventional peritectically solidifying alloys. © 2014 Elsevier Ltd.


Werner R.,University of Leoben | Schwaighofer E.,University of Leoben | Schloffer M.,University of Leoben | Clemens H.,University of Leoben | And 2 more authors.
Advanced Materials Research | Year: 2014

In the present study the high-temperature deformation behavior of a caste and subsequently HIPed β-solidifying γ-TiAl-based alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at. %), termed TNM alloy, is investigated. At room temperature this alloy consists of ordered g- TiAl, α2-Ti3Al and βo-TiAl phases. By increasing the temperature, α2 and βo disorder to α and β, respectively. In order to get a better understanding of dynamic recovery and recrystallization processes during thermomechanical processing, isothermal compression tests on TNM specimens are carried out on a Gleeble®3500 simulator. These tests are conducted at temperatures ranging from 1100 °C to 1250 °C (in the α/α2+β/βo+γ phase field region) applying strain rates in the range of 0.005 s-1 to 0.5 s-1 up to a true strain of 0.9. The evolution of microstructure along with the dynamically recrystallized grain size during hot deformation is examined by scanning electron microscopy (SEM). The flow softening behavior after reaching the peak stress in the true stress-true strain curve is attributed to dynamic recrystallization. By using the Zener-Hollomon parameter as a temperaturecompensated strain rate the dependence of flow stress on temperature and strain rate is shown to follow a hyperbolic-sine Arrhenius-type relationship. © (2014) Trans Tech Publications, Switzerland.


Schwaighofer E.,University of Leoben | Schloffer M.,University of Leoben | Schmoelzer T.,University of Leoben | Mayer S.,University of Leoben | And 4 more authors.
Praktische Metallographie/Practical Metallography | Year: 2012

Intermetallic titanium aluminides are employed in aircraft engines and automobile engines because of their low density and excellent high-temperature properties Today's TiAI-based alloys are multi-phase alloys of a complex structure which mainly consist of γ-TiAl, α 2-T1 3AI and low fractions of a β 0-TiAI phase. An example of such an alloy is the so-called TNM alloy which exhibit a nominal composition of Ti-43 5AI-4Nb-1 Mo-0.1 B (in at.%) In this alloy, solidification takes place via the p-phase, with the consequence of a finegrained and nearly segregation-free micro-structure In spite of that, the cast microstruc-ture also contains coarser grains which can act as crack initiators at room temperature and will reduce the deformation capability during tensile tests. Within the framework of this paper, heat treatment studies were conducted on a cast and hot isostatically pressed material with the primary aim of a microstruc-tural homogenization in order to reduce the crack-initiating microstructural components and, hence, increase its fracture elongation at room temperature. In further heat treatments, microstructures with balanced mechanical properties were adjusted.


Schwaighofer E.,University of Leoben | Clemens H.,University of Leoben | Mayer S.,University of Leoben | Lindemann J.,TU Brandenburg | And 4 more authors.
Intermetallics | Year: 2014

Advanced intermetallic multi-phase γ-TiAl based alloys, such as TNM alloys with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at.%), are potential candidates to replace heavy Ni-base superalloys in the next generation of aircraft and automotive combustion engines. Aimed components are turbine blades and turbocharger turbine wheels. Concerning the cost factor arising during processing, which - additionally to material costs - significantly influences the final price of the desired components, new processing solutions regarding low-cost and highly reliable production processes are needed. This fundamental study targets the replacement of hot-working, i.e. forging, for the production of turbine blades. But without forging no grain refinement takes place by means of a recrystallization process because of the lack of stored lattice defects. Therefore, new heat treatment concepts have to be considered for obtaining final microstructures with balanced mechanical properties in respect to sufficient tensile ductility at room temperature as well as high creep strength at elevated temperatures. This work deals with the adjustment of microstructures in a cast and heat-treated TNM alloy solely by exploiting effects of phase transformations and chemical driving forces due to phase imbalances between different heat treatment steps and compares the mechanical properties to those obtained for forged and heat-treated material. © 2013 Elsevier Ltd. All rights reserved.


Decker S.,TU Bergakademie Freiberg | Lindemann J.,GfE Fremat GmbH | Kruger L.,TU Bergakademie Freiberg
Materials Science and Engineering A | Year: 2016

A composite material consisting of a Ti-6Al-4V matrix and 10 wt% and 20 wt% TiAl particles respectively, was synthesized by Spark Plasma Sintering (SPS). The microstructure and mechanical properties of both composite conditions are investigated and compared with those of the unreinforced matrix material. Tensile properties are analyzed in the temperature range from room temperature to 550 °C. Due to the particle reinforcement, the ultimate tensile strength increases in the temperature range between 300 °C and 550 °C significantly. The results prove the potential of TiAl particle reinforced titanium alloys as light weight material in the temperature range between 450 and 650 °C. © 2016 Elsevier B.V.


Godor F.,University of Leoben | Werner R.,University of Leoben | Lindemann J.,GfE Fremat GmbH | Clemens H.,University of Leoben | Mayer S.,University of Leoben
Praktische Metallographie/Practical Metallography | Year: 2015

In this contribution, the microstructure of two intermetallic γ-TiAI-based alloys with different Al contents were examined after high-temperature deformation. To investigate the dynamic recrystallization of these alloys, isothermal compression tests were performed using a Gleeble® 3500 simulator. For the experiments, a temperature range of 1150°C to 1300°C and strain rates of 0.005 s-1 0.05 s-1 and 0.5 s-1 were applied, up to a true strain of 0.9. The deformed microstructural states, particularly the multiphase alloys' dynamically recrystallized grain sizes were characterized via Scanning Electronic Microscopy (SEM) and Electron Back Scatter Diffraction (EBSD). The recrystallized grain sizes obtained from the experiments could be linked with the calculated Zener-Hollomon parameter through a power law. © Carl Hanser Verlag, München.


Kirschner M.,Max Planck Institute for Physics | Wobst T.,Rolls-Royce | Rittmeister B.,GfE Fremat GmbH | Mundt Ch.,Max Planck Institute for Physics
Proceedings of the ASME Turbo Expo | Year: 2014

One of the major problems facing the users of aircraft engines and stationary gas turbines in dusty and dirty environments is erosion, causing engine performance deterioration. Thermal barrier coatings (TBCs) are often applied on metal engine components as combustor heat shields or tiles as well as turbine blades allowing enhanced operating temperatures and resulting in increased thermal efficiency of the turbine and also reduced fuel consumption and gaseous emission. Erosive attack by airborne dust or fly ash, coarse particles causes coating degradation resulting in lifing issues of engine components. In the present study an erosion test facility was used to simulate the mechanisms of coating degradation expected in gas turbines in a more realistic way closer to real engine conditions. A loading situation combining thermal gradient cycling and erosive media was used. The experiments has been performed with an arc heated plasma wind tunnel (total enthalpy up to 20 MJ/kg), which is available at the Institute for Thermodynamics at the University of the Federal Armed Forces in Munich, Germany. The experimental setup and the integration of the air jet erosion test rig into the existing plasma wind tunnel will be elucidated. Different plasma sprayed thermal barrier coating materials, including the standard TBC material yttria-stabilised zirconia, were investigated regarding their erosion resistance. For validation and verification, samples of nickel-based Mar-M 247 and INCO 718 alloys have been used. Copyright © 2014 by ASME.


Godor F.,University of Leoben | Werner R.,University of Leoben | Lindemann J.,GfE Fremat GmbH | Clemens H.,University of Leoben | Mayer S.,University of Leoben
Materials Science and Engineering A | Year: 2015

Intermetallic titanium aluminides are promising candidates for high-temperature components in aero and automotive applications. To enable good processing characteristics with an optimized final microstructure, the hot-working parameters and the fraction of the β/βo-TiAl phase at deformation temperature are of particular interest. Therefore, the high-temperature deformation behavior of two γ-TiAl based alloys with the nominal compositions Ti-41Al-3Mo-0.5Si-0.1B and Ti-45Al-3Mo-0.5Si-0.1B, in at%, was studied. At room temperature both alloys contain the ordered phases γ-TiAl, βo-TiAl and small amounts of α2-Ti3Al. In order to investigate dynamic restoration during thermomechanical processing, isothermal compression tests were conducted on a Gleeble®3500 simulator and corresponding flow curves were measured. The tests were carried out at temperatures from 1150°C to 1300°C, applying strain rates ranging from 0.005s-1 to 0.5s-1, up to a true strain of 0.9. The deformed microstructural states of the multiphase alloys, particularly the dynamically recrystallized grain sizes, were characterized by means of scanning electron microscopy and electron back-scatter diffraction. To compare the microstructure right before and after deformation heat treatments were additionally performed at the same temperatures as the compression tests were carried out. The experimentally determined flow stress data were described with two different constitutive models (Sellars-McTegart model, Hensel-Spittel model). The experimentally determined dynamically recrystallized grain sizes of the hot-deformed microstructures were linked with the Zener-Hollomon parameter calculated from the simulation through a power law. © 2015 Elsevier B.V.

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