scholarly journals Phase Equilibria and Phase Transformations in Molybdenum-Containing TiAl Alloys

2011 ◽  
Vol 1295 ◽  
Author(s):  
Svea Mayer ◽  
Christian Sailer ◽  
Hirotoyo Nakashima ◽  
Thomas Schmoelzer ◽  
Thomas Lippmann ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Ternary Phase Diagram ◽  
Isothermal Heat Treatment ◽  
Transition Temperatures ◽  
Scanning Calorimetry ◽  
Tial Alloys ◽  
Β Phase ◽  
The Individual

ABSTRACTMolybdenum, being a strong β stabilizer, is an important alloying element in TiAl alloys, since a significant volume fraction of the disordered bcc β-phase at elevated temperatures improves the processing characteristics during hot-working. Unfortunately, the effect of Mo on the individual phases and their transition temperatures is not completely known but is necessary for designing engineering applications. In this paper, sections of the Ti-Al-Mo ternary phase diagram derived from thermodynamic calculations as well as experimental data are presented. Further, the phase transition temperatures given by the phase diagrams are compared with results from isothermal heat treatment studies, differential scanning calorimetry measurements and in-situ high-temperature diffraction experiments. Combining all of these results, a revised phase diagram is proposed.

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.

High Temperature Oxidation Protection of Multi-Phase Mo-Containing TiAl-Alloys by the Fluorine Effect

2012 ◽  
Vol 1516 ◽  
pp. 95-100 ◽  
Author(s):  
Alexander Donchev ◽  
Raluca Pflumm ◽  
Svea Mayer ◽  
Helmut Clemens ◽  
Michael Schütze
Keyword(s):  
High Temperature ◽  
Oxidation Resistance ◽  
Titanium Aluminides ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Temperature Oxidation ◽  
Tial Alloys ◽  
Β Phase ◽  
Multi Phase ◽  
The Impact

ABSTRACTIntermetallic titanium aluminides are potential materials for application in high temperature components. In particular, alloys solidifying via the β-phase are of great interest because they possess a significant volume fraction of the disordered body-centered cubic β-phase at elevated temperatures ensuring good processing characteristics during hot-working. Nevertheless, their practical use at temperatures as high as 800°C requires improvements of the oxidation resistance. This paper reports on the fluorine effect on a multi-phase TiAl-alloy in the cast and hot-isostatically pressed condition at 800°C in air. The behavior of the so-called TNM material (Ti-43.5Al-4Nb-1Mo-0.1B, in at %) was compared with that of two other TiAl-alloys which are Nb-free and contain different amounts of Mo (3 and 7 at%, respectively). The oxidation resistance of the fluorine treated samples was significantly improved compared to the untreated samples. After fluorine treatment all alloys exhibit slow alumina kinetics indicating a positive fluorine effect. Results of isothermal and thermocyclic oxidation tests at 800°C in air are presented and discussed in the view of composition and microstructure of the TiAl-alloys investigated, along with the impact of the fluorine effect on the oxidation resistance of these materials.

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.

Design Approaches and Achievements of Novel Wrought TiAl Alloys for Jet Engine Applications

MRS Advances ◽  
2019 ◽  
Vol 4 (25-26) ◽  
pp. 1465-1470
Author(s):  
Hideki Wakabayashi ◽  
Loris J. Signori ◽  
Ali Shaaban ◽  
Ryosuke Yamagata ◽  
Hirotoyo Nakashima ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Phase Transformation ◽  
Hot Workability ◽  
Tial Alloys ◽  
Jet Engine ◽  
Crack Propagation Resistance ◽  
Β Phase ◽  
Transformation Pathway ◽  
Component Systems ◽  
Multi Component System

AbstractDesign approaches and achievements for the development of wrought TiAl alloys to be used for LPT and HPC blades are constructed. In case of Ti-Al-M1-M2 quaternary systems, conventional equivalency concept does not work for the alloy design, and a new thermodynamic database for phase diagram calculations in multi-component systems of the alloys is built by introducing the interaction parameters among four phases of β−Ti, α2−Ti3Al, α−Ti and γ−TiAl phases in the systems, in order to reproduce the experimentally determined phase diagrams. Based on the phase diagram calculations, the composition range of a unique phase transformation pathway of β+α→α→β+γ in the multi-component system can be identified, and thus model alloys with excellent hot workability even at higher strain rate and mechanical properties can be successfully proposed. It can be concluded that an introduction of bcc β phase and the morphology control through the phase transformation pathway make it possible to improve the room temperature ductility, creep and fatigue crack propagation resistance.

Thermodynamics and Microstructure of Co-V8C7 Alloy

2005 ◽  
Vol 492-493 ◽  
pp. 523-530 ◽  
Author(s):  
Shui Gen Huang ◽  
Lin Li ◽  
Jef Vleugels ◽  
Omer Van der Biest
Keyword(s):  
Phase Diagram ◽  
Vertical Section ◽  
Carbon Activity ◽  
Calphad Method ◽  
Model Parameters ◽  
Dsc Analysis ◽  
Scanning Calorimetry ◽  
Isothermal Sections ◽  
Forming Temperature ◽  
The Individual

The thermodynamic properties of the Co-V-C and Co-V8C7 systems are of interest for superfine cemented carbide applications. The model parameters for the Gibbs energy of the individual phases have been evaluated using the CALPHAD method by combining the recently optimized phase diagram information of the V-C, Co-C and Co-V system. The isothermal sections of ternary system Co-V-C at 1400 °C and 1600 °C, as well as the vertical section of Co-V8C7 system were extrapolated. The calculated results, especially the liquid forming temperature of Co-V8C7 system was validated with experiments by using differential scanning calorimetry (DSC) analysis. Through controlling the carbon activity, various vertical sections with different carbon activity in Co-V8C7 system are presented.

scholarly journals Atom Probe Field Ion Microscopy of Model Ni-Al-Be Superalloys

1997 ◽  
Vol 3 (S2) ◽  
pp. 695-696
Author(s):  
R. C. Thomson ◽  
K. F. Russell ◽  
M. K. Miller
Keyword(s):  
Phase Diagram ◽  
Ternary Phase ◽  
Volume Fraction ◽  
Ternary Phase Diagram ◽  
Operating Temperature ◽  
Light Element ◽  
Atom Probe ◽  
Jet Engines ◽  
Probe Field ◽  
Ion Microscopy

Nickel-based superalloys used in jet engines consist of a face-centred cubic Ni matrix, γ, containing a high density of Ll2-ordered Ni3Al precipitates, γ´. At high temperatures the strength of the alloy depends primarily on the strength of the γ´ phase, which begins to decrease above approximately 750°C, limiting the maximum operating temperature of the superalloy. The possibility of strengthening the γ´ phase by solid-state precipitation within the γ´ phase has been investigated in model Ni-Al superalloys containing Be. Beryllium, a light element, is also expected to be a potent solid solution strengthener in the γ´ matrix.Four alloys were manufactured with compositions Ni-18.8 at. % Al-1.6% Be, Ni-19.0 at. % Al-2.6% Be, Ni-17.9 at. % Al-5.4% Be and Ni-15.9 at. % Al-11.9% Be. These Al levels result in a volume fraction of γ´ phase similar to that present in a commercial superalloy, and the Be addition places the superalloys in the γ-γ´-NiBe region of the ternary phase diagram, Fig. 1.

Calculation of Aluminum Equivalent Based on Thermo-Calc Software in Ti-Al-Nb Ternary System

2014 ◽  
Vol 788 ◽  
pp. 144-149 ◽  
Author(s):  
Hui Min Yang ◽  
Liang Shun Luo ◽  
Mei Hui Song ◽  
Hai Qun Qi ◽  
Chun Yan Wang ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Ternary Phase ◽  
Ternary Phase Diagram ◽  
Primary Phase ◽  
Ternary Alloys ◽  
Al Content ◽  
Β Phase ◽  
Thermo Calc Software ◽  
Vertical Sections ◽  
Aluminum Equivalent

Ti-Al-Nb ternary phase diagrams were calculated by Thermo-Calc software. The analysis of the calculated vertical sections of Ti-Al-Nb phase diagram indicated that when Nb content is fixed at 5at.% and Al content is lower than 52.3at.%, the primary phase would be β phase during solidification. With 10 at.%Nb and Al content lower than 55.8at.%, or with 15 at.%Nb and Al content lower than 56.9at.%, the primary phase would be β phase. The vertical sections of Ti-Al-Nb ternary phase diagram were further simplified into pseudo-Ti-Al binary phase diagram. According to the pseudo-Ti-Al diagram, the expression of the aluminum equivalent was obtained in Ti-Al-5Nb ternary alloys.

Thermal Stability of Severe Plastically Deformed VT-6 (Ti-6Al-4V)

2008 ◽  
Vol 584-586 ◽  
pp. 893-898 ◽  
Author(s):  
Henry J. Rack ◽  
Javaid Qazi ◽  
L. Allard ◽  
Ruslan Valiev
Keyword(s):  
Thermal Stability ◽  
Volume Fraction ◽  
Tem Analysis ◽  
Β Phase ◽  
Transmission Electron ◽  
Continuous Recrystallization ◽  
Hardness Increase ◽  
Lower Temperature ◽  
The Individual ◽  
Thermal Stability Of

The thermal stability of equal channel angular extruded VT-6(Ti-6Al-4V) has been examined using micro-hardness, nano-hardness of the individual αand β phases backscattered scanning (BSEI) and transmission electron microscopy (TEM). After straining to an equivalent total equivalent of 6.5 samples were annealed for 1 h at temperatures between 175 and 800 o C followed by water quenching. Micro and nano-hardness measurements showed an initial hardness increase, the former rising to a maximum at 175°C, while the latter exhibited a maximum at 500°C. BSEI and TEM analysis showed that these observations can be understood by considering the microstructure changes occurring at different length scales. Annealing in the temperature range of 175 to 500°C did not significantly alter the α and β particle size, while TEM showed that recovery and continuous recrystallization occurred in the α phase, higher temperatures being required to activate the recovery and recrystallization processes within the β phase. Finally at temperatures above 600°C spheroidization and growth of the β phase occurred with the volume fraction of this phase increasing from 15 pct at lower temperature to 25 pct at 800°C, an equi-axed α+ β microstructure being observed at this temperature.

Detection of Phase Transition in Free-Cutting Al-Mg-Si Alloys by Resonant Ultrasound Spectroscopy

2014 ◽  
Vol 794-796 ◽  
pp. 21-26 ◽  
Author(s):  
Jitka Nejezchlebová ◽  
Hanuš Seiner ◽  
Miroslav Karlík
Keyword(s):  
Volume Fraction ◽  
Thermal Hysteresis ◽  
Transition Process ◽  
Transition Temperatures ◽  
Scanning Calorimetry ◽  
Resonant Ultrasound Spectroscopy ◽  
Dsc Measurements ◽  
Temperature Ranges ◽  
Small Volume Fraction ◽  
Resonant Ultrasound

The transition temperatures of small amounts of eutectic particles contained in free-cutting aluminum alloys (namely AA6262 and AA6023) are investigated in this paper. Detection of the transition temperatures by conventional differential scanning calorimetry (DSC) measurements is difficult because of the small volume fraction (~ 1wt.%) of the eutectic. On the other hand, the melting of the particles induces small changes of elastic moduli of the alloy, which can be sensitively measured by resonant acoustic methods, for example by resonant ultrasound spectroscopy (RUS). It is shown that the phase transitions of the particles correspond to well-detectable changes of the resonant spectrum, which enables a more detailed characterization of the transition process. A significant thermal hysteresis is observed between the cooling and the heating runs, and also the widths of the temperature ranges in which the transitions occur exhibit a strong melting/freezing asymmetry.

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.

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