Physical Metallurgy and Properties of β-solidifying TiAl Based Alloys

2011 ◽  
Vol 1295 ◽  
Author(s):  
Helmut Clemens ◽  
Thomas Schmoelzer ◽  
Martin Schloffer ◽  
Emanuel Schwaighofer ◽  
Svea Mayer ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
Volume Fraction ◽  
High Energy ◽  
Heat Treatments ◽  
Hot Working ◽  
Physical Metallurgy ◽  
Compression Tests ◽  
Phase Volume Fraction ◽  
Β Phase

ABSTRACTIn this paper, the physical metallurgy and properties of a novel family of high-strength γ-TiAl-based alloys is reviewed succinctly. These so-called TNM™ alloys contain Nb and Mo additions in the range of 3 - 7 atomic percent as well as small additions of B and C. For the definition of the alloy composition thermodynamic calculations using the CALPHAD method were conducted. The predicted phase transformation and ordering temperatures were verified by differential scanning calorimetry and in situ high-energy X-ray diffraction. TNM alloys solidify via the β-phase and exhibit an adjustable β-phase volume fraction at temperatures, where hot-working processes are performed. Due to the high volume fraction of β-phase these alloys can be processed isothermally as well as under near conventional conditions. In order to study the occurring deformation and recrystallization processes during hot-working, in situ diffraction experiments were conducted during compression tests at elevated temperatures. With subsequent heat-treatments a significant reduction of the β-phase is achieved. These outstanding features of TNM alloys distinguish them from other TiAl alloys which must exclusively be processed under isothermal conditions and/or which always exhibit a high fraction of β-phase at service temperature. After hot-working and multi-step heat-treatments, these alloys show yield strength levels > 800 MPa at room temperature and also good creep resistance at elevated temperatures.

scholarly journals Phase Transition and Ordering Temperatures of TiAl-Mo Alloys Investigated by In Situ Diffraction Experiments

2010 ◽  
Vol 654-656 ◽  
pp. 456-459 ◽  
Author(s):  
Thomas Schmoelzer ◽  
Svea Mayer ◽  
Frank Haupt ◽  
Gerald A. Zickler ◽  
Christian Sailer ◽  
...  
Keyword(s):  
Ternary Phase ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Ternary Phase Diagram ◽  
High Energy ◽  
The Body ◽  
Alloying Element ◽  
Tial Alloys ◽  
Β Phase

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.

Processing Map for Zr-based In-situ β Phase Composites

2007 ◽  
Vol 1048 ◽  
Author(s):  
Seung-Yub Lee ◽  
John J.Z. Li ◽  
Jin-yoo Suh ◽  
Won-Kyu Rhim ◽  
William L. Johnson ◽  
...  
Keyword(s):  
Processing Map ◽  
Volume Fraction ◽  
Processing Condition ◽  
Phase Evolution ◽  
High Energy ◽  
High Temperature Phase ◽  
Composition Analysis ◽  
Temperature Phase ◽  
Β Phase

AbstractThe processing map for Zr-based bulk metallic glasses with crystalline in-situ precipitates (â phase) has been constructed from high temperature phase information, chemical composition analysis, and â phase crystallization kinetics. The phase evolution was detected in-situ by high energy synchrotron X-ray, and kinetic information on crystalline phase was measured from electrostatic levitation facility (ESL). This processing map offers a unique opportunity to control both volume and size of the dendritic â phase through composition and processing condition manipulation. The volume fraction of â phase can be customized from 6% to 93 %, and dendrite size is controllable between 1 and 50 µm at the current stage.

scholarly journals The Transformation Mechanism of β Phase to ω-Related Phases in Nb-Rich γ-TiAl Alloys Studied by In Situ High-Energy X-Ray Diffraction

2013 ◽  
Vol 772 ◽  
pp. 85-89 ◽  
Author(s):  
Andreas Stark ◽  
Michael Oehring ◽  
Florian Pyczak ◽  
Thomas Lippmann ◽  
Lars Lottermoser ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
High Energy ◽  
X Ray Diffraction ◽  
Transformation Mechanism ◽  
Quenching Rate ◽  
Repeated Heating ◽  
X Ray ◽  
Β Phase ◽  
Diffusion Controlled

In recent years intermetallic γ-TiAl based alloys with additional amounts of the ternary bcc β Ti(Al,Nb) phase attracted increasing attention due to their improved workability at elevated temperatures. Depending on alloy composition and heat treatment the ductile high-temperature β phase can transform to several ordered phases at lower temperatures. However, currently available phase diagrams of these multiphase alloys are quite uncertain and the precipitation kinetics of some metastable phases is far from understood. In the present study various transformation pathways of the third phase were observed in situ by means of high-energy X-ray diffraction using synchrotron radiation. A Ti-45Al-10Nb (at.%) specimen was subjected to a temperature ramp of repeated heating cycles (700 °C - 1100 °C) with subsequent quenching at different rates. Depending on the quenching rate reversible transformations of the B2-ordered βo phase to different ω-related phases were observed. The results indicate that the complete transformation from βo to hexagonal B82-ordered ωo consists of two steps which are both diffusion controlled but proceed with different velocities.

Hot-die Forging of a β-stabilized γ-TiAl Based Alloy

2008 ◽  
Vol 1128 ◽  
Author(s):  
Wilfried Wallgram ◽  
Helmut Clemens ◽  
Sascha Kremmer ◽  
Andreas Otto ◽  
Volker Güther
Keyword(s):  
Mechanical Properties ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Small Deformation ◽  
High Volume ◽  
Compression Tests ◽  
Tial Alloys ◽  
Β Phase ◽  
Heat Treated ◽  
Hot Die Forging

AbstractBecause of the small “deformation window” hot-working of γ-TiAl alloys is a complex and difficult task and, therefore, isothermal forming processes are favoured. In order to increase the deformation window a novel Nb and Mo containing γ-TiAl based alloy (TNM™ alloy) was developed. Due to a high volume fraction of β-phase at elevated temperatures the alloy can be hot-die forged under near conventional conditions, which means that conventional forging equipment with minor and inexpensive modifications can be used. With subsequent heattreatments balanced mechanical properties can be achieved. This paper summarizes our progress in establishing a “near conventional” forging route for the fabrication of γ-TiAl components. The results of lab scale compression tests and forging trials on an industrial scale are included. In addition, the mechanical properties of forged and heat-treated TNM™ material are presented.

scholarly journals Enhancing the High-Temperature Strength of a Co-Base Superalloy by Optimizing the γ/γ′ Microstructure

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 321
Author(s):  
D. Hausmann ◽  
C. Solís ◽  
L.P. Freund ◽  
N. Volz ◽  
A. Heinemann ◽  
...  
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Volume Fraction ◽  
Heat Treatments ◽  
Age Hardening ◽  
Precipitate Size ◽  
High Temperature Strength ◽  
Compression Tests ◽  
Transmission Electron

Compositionally complex polycrystalline γ/γ′ CoNi-base superalloys, such as CoWAlloy2 (Co41-Ni32-Cr12-Al9-W5-Ti0.3-Ta0.2-Si0.4-Hf0.1-C-B-Zr) are interesting candidates for new high-temperature materials. To maximize their high-temperature strength, the γ/γ′ microstructure has to be optimized by adjusting the multi-step heat treatments. Various microstructures after different heat treatments were analyzed by scanning and transmission electron microscopy and especially in-situ small-angle neutron scattering during heat treatment experiments. The corresponding mechanical properties were determined by compression tests and hardness measurements. From this, an optimum γ′ precipitate size was determined that is adjusted mainly in the first precipitation heat treatment step. This is discussed on the basis of the theory of shearing of γ′ precipitates by weak and strong pair-couplings of dislocations. A second age hardening step leads to a further increase in the γ′ volume fraction above 70% and the formation of tertiary γ′ precipitates in the γ channels, resulting in an increased hardness and yield strength. A comparison between two different three-step heat treatments revealed an increase in strength of 75 MPa for the optimized heat treatment.

scholarly journals Pseudo-binary phase diagram for Zr-based in situ β phase composites

2007 ◽  
Vol 22 (2) ◽  
pp. 538-543 ◽  
Author(s):  
S.Y. Lee ◽  
C.P. Kim ◽  
J.D. Almer ◽  
U. Lienert ◽  
E. Ustundag ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Volume Fraction ◽  
Equilibrium Phase ◽  
High Energy ◽  
High Temperature Phase ◽  
Composition Analysis ◽  
Temperature Phase ◽  
Quasi Equilibrium ◽  
Β Phase

The pseudo-binary (quasi-equilibrium) phase diagram for Zr-based bulk metallic glasses with crystalline in situ precipitates (β phase) has been constructed from high-temperature phase information and chemical composition analysis. The phase evolution was detected in situ by high-energy synchrotron x-ray diffraction followed by Rietveld analysis of the data for volume fraction estimation. The phase diagram delineates phase fields and allows the control of phase fractions. Combined with related previous work by the authors, this diagram offers a unique opportunity to control both the morphology and volume of the dendritic β phase precipitates to enhance the properties of the composites.

Electron and ion irradiation-induced dissolution of mechanical twins in the intermetalic U3Si: An in situ HVEM study

1989 ◽  
Vol 47 ◽  
pp. 652-653
Author(s):  
Charles W. Allen ◽  
Robert C. Birtcher
Keyword(s):  
Elevated Temperatures ◽  
Ion Irradiation ◽  
Ion Beam ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Heavy Ion ◽  
High Energy ◽  
Mechanical Twinning ◽  
In Situ Experiments

The uranium silicides, including U3Si, are under study as candidate low enrichment nuclear fuels. Ion beam simulations of the in-reactor behavior of such materials are performed because a similar damage structure can be produced in hours by energetic heavy ions which requires years in actual reactor tests. This contribution treats one aspect of the microstructural behavior of U3Si under high energy electron irradiation and low dose energetic heavy ion irradiation and is based on in situ experiments, performed at the HVEM-Tandem User Facility at Argonne National Laboratory. This Facility interfaces a 2 MV Tandem ion accelerator and a 0.6 MV ion implanter to a 1.2 MeV AEI high voltage electron microscope, which allows a wide variety of in situ ion beam experiments to be performed with simultaneous irradiation and electron microscopy or diffraction.At elevated temperatures, U3Si exhibits the ordered AuCu3 structure. On cooling below 1058 K, the intermetallic transforms, evidently martensitically, to a body-centered tetragonal structure (alternatively, the structure may be described as face-centered tetragonal, which would be fcc except for a 1 pet tetragonal distortion). Mechanical twinning accompanies the transformation; however, diferences between electron diffraction patterns from twinned and non-twinned martensite plates could not be distinguished.

scholarly journals Hot Workability of 300M Steel Investigated by In Situ and Ex Situ Compression Tests

Metals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 880 ◽  
Author(s):  
Rongchuang Chen ◽  
Haifeng Xiao ◽  
Min Wang ◽  
Jianjun Li
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Hot Working ◽  
Ex Situ ◽  
Lower Strain Rate ◽  
Hot Workability ◽  
Compression Tests ◽  
300M Steel ◽  
Lower Strain

In this work, hot compression experiments of 300M steel were performed at 900–1150 °C and 0.01–10 s−1. The relation of flow stress and microstructure evolution was analyzed. The intriguing finding was that at a lower strain rate (0.01 s−1), the flow stress curves were single-peaked, while at a higher strain rate (10 s−1), no peak occurred. Metallographic observation results revealed the phenomenon was because dynamic recrystallization was more complete at a lower strain rate. In situ compression tests were carried out to compare with the results by ex situ compression tests. Hot working maps representing the influences of strains, strain rates, and temperatures were established. It was found that the power dissipation coefficient was not only related to the recrystallized grain size but was also related to the volume fraction of recrystallized grains. The optimal hot working parameters were suggested. This work provides comprehensive understanding of the hot workability of 300M steel in thermal compression.

scholarly journals Two-dimensional inorganic molecular crystals

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Wei Han ◽  
Pu Huang ◽  
Liang Li ◽  
Fakun Wang ◽  
Peng Luo ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Electronic Devices ◽  
Molecular Crystals ◽  
High Energy ◽  
Two Dimensional ◽  
Β Phase ◽  
Α Phase ◽  
Growth Plane ◽  
Transmission Electron

Abstract Two-dimensional molecular crystals, consisting of zero-dimensional molecules, are very appealing due to their novel physical properties. However, they are mostly limited to organic molecules. The synthesis of inorganic version of two-dimensional molecular crystals is still a challenge due to the difficulties in controlling the crystal phase and growth plane. Here, we design a passivator-assisted vapor deposition method for the growth of two-dimensional Sb2O3 inorganic molecular crystals as thin as monolayer. The passivator can prevent the heterophase nucleation and suppress the growth of low-energy planes, and enable the molecule-by-molecule lateral growth along high-energy planes. Using Raman spectroscopy and in situ transmission electron microscopy, we show that the insulating α-phase of Sb2O3 flakes can be transformed into semiconducting β-phase under heat and electron-beam irradiation. Our findings can be extended to the controlled growth of other two-dimensional inorganic molecular crystals and open up opportunities for potential molecular electronic devices.

scholarly journals In-Situ Characterization by High-Energy X-ray Diffraction of the Phase Transformations Leading to Transformation-Induced Plasticity-Aided Bainitic Steel

2019 ◽  
Vol 3 (4) ◽  
pp. 25
Author(s):  
Zélie Tournoud ◽  
Frédéric De Geuser ◽  
Gilles Renou ◽  
Didier Huin ◽  
Patricia Donnadieu ◽  
...  
Keyword(s):  
Carbon Content ◽  
Phase Transformations ◽  
High Energy ◽  
Heat Treatments ◽  
Treatment Temperature ◽  
Bainitic Steel ◽  
X Ray Diffraction ◽  
Transformation Induced Plasticity ◽  
X Ray

The phase transformations occurring during the heat treatments leading to transformation-induced plasticity (TRIP)-aided bainitic steel have been investigated in-situ by high-energy X-ray diffraction (HEXRD) conducted with synchrotron light at 90 keV. Direct microstructure characterization has been performed by electron microscopy using electron backscatter diffraction and orientation and phase mapping in a transmission electron microscope. HEXRD data allow the quantification of the evolution of the austenite phase fraction with the heat treatments, as well as its carbon content and the fraction of carbides, from the lattice parameter evolution. It is shown that different combinations of austenite fraction and carbon content can be reached by adjusting the heat treatment temperature.

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