Pathways of phase transformation in β-phase-stabilized σ/γ-TiAl alloys subjected to two-step heat treatments

2018 ◽  
Vol 149 ◽  
pp. 70-74 ◽  
Author(s):  
Thomas Klein ◽  
David Holec ◽  
Helmut Clemens ◽  
Svea Mayer
Keyword(s):  
Phase Transformation ◽  
Heat Treatments ◽  
Tial Alloys ◽  
Β Phase

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.

Phase Transformation In Ti-6al-4v Alloys

1972 ◽  
Vol 30 ◽  
pp. 584-585
Author(s):  
Shiro Fujishiro
Keyword(s):  
Phase Transformation ◽  
Grain Boundary ◽  
Cryogenic Temperature ◽  
Β Phase ◽  
Heat Treated ◽  
Mixed Microstructure ◽  
Ductile Behavior

The Ti-6 wt.% Al-4 wt.% V commercial alloys have exhibited an improved formability at cryogenic temperature when the alloys were heat-treated prior to the tests. The author was interested in further investigating this unusual ductile behavior which may be associated with the strain-induced transformation or twinning of the a phase, enhanced at lower temperatures. The starting materials, supplied by RMI Co., Niles, Ohio were rolled mill products in the form of 40 mil sheets. The microstructure of the as-received materials contained mainly ellipsoidal α grains measuring between 1 and 5μ. The β phase formed an undefined grain boundary around the a grains. The specimens were homogenized at 1050°C for one hour, followed by aging at 500°C for two hours, and then quenched in water to produce the α/β mixed microstructure.

Microstructural and Microchemical Characterization of Nickel Sulfide Inclusions in Plate Glass

1991 ◽  
Vol 49 ◽  
pp. 962-963
Author(s):  
J. Cooper ◽  
O. Popoola ◽  
W. M. Kriven
Keyword(s):  
Thermal Expansion ◽  
Phase Transformation ◽  
Glass Matrix ◽  
Nickel Sulfide ◽  
Plate Glass ◽  
Thermal Expansion Mismatch ◽  
Volume Increase ◽  
Β Phase ◽  
Microchemical Characterization

Nickel sulfide inclusions have been implicated in the spontaneous fracture of large windows of tempered plate glass. Two alternative explanations for the fracture-initiating behaviour of these inclusions have been proposed: (1) the volume increase which accompanies the α to β phase transformation in stoichiometric NiS, and (2) the thermal expansion mismatch between the nickel sulfide phases and the glass matrix. The microstructure and microchemistry of the small inclusions (80 to 250 μm spheres), needed to determine the cause of fracture, have not been well characterized hitherto. The aim of this communication is to report a detailed TEM and EDS study of the inclusions.

γ→β phase transformation in Ti-42.9Al-4.6Nb–2Cr

2021 ◽  
Vol 133 ◽  
pp. 107169
Author(s):  
R.R. Xu ◽  
M.Q. Li
Keyword(s):  
Phase Transformation ◽  
Β Phase

The Use of In Situ Characterization Techniques for the Development of Intermetallic Titanium Aluminides

2014 ◽  
Vol 783-786 ◽  
pp. 2097-2102 ◽  
Author(s):  
Svea Mayer ◽  
Emanuel Schwaighofer ◽  
Martin Schloffer ◽  
Helmut Clemens
Keyword(s):  
Titanium Aluminides ◽  
Turbine Blades ◽  
Heat Treatments ◽  
Mechanical Processing ◽  
Tial Alloys ◽  
Solidification Processes ◽  
Consistent Picture ◽  
Aero Engines ◽  
Multi Phase

Urgent needs concerning energy efficiency and environmental politics require novel approaches to materials design. One recent example is thereby the implementation of light-weight intermetallic titanium aluminides as structural materials for the application in turbine blades of aero-engines as well as in turbocharger turbine wheels for the next generation of automotive engines. Each production process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and / or subsequent heat-treatments. To develop sound and sustainable processing routes, knowledge on solidification processes and phase transformation sequences in advanced TiAl alloys is fundamental. Therefore, in-situ diffraction techniques employing synchrotron radiation and neutrons were used for establishing phase fraction diagrams, investigating advanced heat-treatments as well as for optimizing thermo-mechanical processing. Summarizing all results a consistent picture regarding microstructure formation and its impact on mechanical properties in advanced multi-phase TiAl alloys can be given.

Effects of a pre-anneal on the mechanical properties of γ-TiAl

2000 ◽  
Vol 646 ◽  
Author(s):  
Fabienne Grégori ◽  
Philippe Penhoud ◽  
Patrick Veyssière
Keyword(s):  
Mechanical Properties ◽  
Yield Stress ◽  
Alloy Composition ◽  
Heat Treatments ◽  
Tial Alloys ◽  
Clear Effect ◽  
Interstitial Atoms

ABSTRACTThe temperature, TP, and the stress, σP, at which the yield stress of γ-TiAl alloys peaks are influenced by factors such as alloy composition and load orientation. Available data indicates that in the absence of adequate heat treatments, TP and σP are shifted towards values significantly higher than those of samples pre-annealed in order to precipitate interstitial atoms. Conditions under which precipitation influences the anomalous regime are revealed by dedicated tests. In addition to pointing out the clear effect of interstitials, these tests suggest that further ordering may contribute to the strength of Al-rich γ-TiAl.

Effect of Alloying and Thermal Processing on Mechanical Properties of TiAl Alloys

2016 ◽  
Vol 258 ◽  
pp. 501-505
Author(s):  
Alice Chlupová ◽  
Milan Heczko ◽  
Karel Obrtlík ◽  
Přemysl Beran ◽  
Tomáš Kruml
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Thermal Processing ◽  
Lamellar Microstructure ◽  
High Strength ◽  
Fatigue Behaviour ◽  
Tial Alloys ◽  
Working Temperature ◽  
Β Phase ◽  
Strength And Ductility

Two γ-based TiAl alloys with 7 at.% of Nb, alloyed with 2 at.% Mo and 0.5 at.% C, were studied. A heat treatment leading to very fine lamellar microstructure was applied on both alloys. Microstructure after the heat treatment was described and mechanical properties including fatigue behaviour were measured. The as-received material alloyed with C possesses high strength and very limited ductility, especially at RT. After application of selected heat treatment it becomes even more brittle; therefore, this process could be considered as not appropriate for this alloy. On the contrary, in the case of Mo alloyed material, both strength and ductility are improved by the heat treatment at RT and usual working temperature (~750 °C). Presence of the β phase is responsible for this effect. The selected heat treatment thus can be an alternative for this alloy to other thermomechanical treatments as high temperature forging.

scholarly journals A Phenomenological Mechanical Material Model for Precipitation Hardening Aluminium Alloys

Metals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1165 ◽  
Author(s):  
Hannes Fröck ◽  
Lukas Vincent Kappis ◽  
Michael Reich ◽  
Olaf Kessler
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Finite Element ◽  
Phase Transformation ◽  
Aluminium Alloys ◽  
Material Model ◽  
Heat Treatments ◽  
Maximum Temperature ◽  
Finite Element Software ◽  
Welding Processes

Age hardening aluminium alloys obtain their strength by forming precipitates. This precipitation-hardened state is often the initial condition for short-term heat treatments, like welding processes or local laser heat treatment to produce tailored heat-treated profiles (THTP). During these heat treatments, the strength-increasing precipitates are dissolved depending on the maximum temperature and the material is softened in these areas. Depending on the temperature path, the mechanical properties differ between heating and cooling at the same temperature. To model this behavior, a phenomenological material model was developed based on the dissolution characteristics and experimental flow curves were developed depending on the current temperature and the maximum temperature. The dissolution characteristics were analyzed by calorimetry. The mechanical properties at different temperatures and peak temperatures were recorded by thermomechanical analysis. The usual phase transformation equations in the Finite Element Method (FEM) code, which were developed for phase transformation in steels, were used to develop a phenomenological model for the mechanical properties as a function of the relevant heat treatment parameters. This material model was implemented for aluminium alloy 6060 T4 in the finite element software LS-DYNA (Livermore Software Technology Corporation).

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