Influence of Quenching Rates on the Transformation of Ternary Phases in Nb-rich γ-TiAl Alloys

2011 ◽  
Vol 1295 ◽  
Author(s):  
Andreas Stark ◽  
Michael Oehring ◽  
Florian Pyczak
Keyword(s):  
Elevated Temperatures ◽  
High Energy ◽  
X Ray Diffraction ◽  
Quenching Rate ◽  
Repeated Heating ◽  
Β Phase ◽  
Third Phase ◽  
Diffusion Controlled ◽  
Temperature Ramp ◽  
Ordered Phases

ABSTRACTIntermetallic γ-TiAl based alloys with additional amounts of the ternary bcc β phase attracted increasing attention in recent years due to their improved workability at elevated temperatures. At lower temperatures the ductile high-temperature β phase can transform to several ordered phases. However, actually 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 transformations of the third phase are observed in situ by means of high-energy x-ray diffraction using synchrotron radiation. A Ti-45Al-10Nb (at.%) specimen is subject 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 are observed in Ti-45Al-10Nb. At low quenching rates the hexagonal B82-ordered ωo phase is formed while at high quenching rates the metastable intermediate trigonal ω’’ phase can be preserved. The results indicate that the complete transformation from βo to hexagonal B82-ordered ωo consists of two steps which are both diffusion controlled.

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.

scholarly journals Residual Stress Evolution during Decomposition of Ti(1-x)Al(x)N Coatings Using High-Energy X-Rays

2006 ◽  
Vol 524-525 ◽  
pp. 619-624 ◽  
Author(s):  
Mark R. Terner ◽  
Peter Hedström ◽  
Jonathan Almer ◽  
J. Ilavsky ◽  
Magnus Odén
Keyword(s):  
Residual Stress ◽  
Phase Separation ◽  
Elevated Temperatures ◽  
High Energy ◽  
Film Plane ◽  
X Rays ◽  
X Ray Diffraction ◽  
Synchrotron Source ◽  
Simultaneous Acquisition ◽  
Initial Stage

Residual stresses and microstructural changes during phase separation in Ti33Al67N coatings were examined using microfocused high energy x-rays from a synchrotron source. The transmission geometry allowed simultaneous acquisition of x-ray diffraction data over 360° and revealed that the decomposition at elevated temperatures occurred anisotropically, initiating preferentially along the film plane. The as-deposited compressive residual stress in the film plane first relaxed with annealing, before dramatically increasing concurrently with the initial stage of phase separation where metastable, nm-scale c-AlN platelets precipitated along the film direction. These findings were further supported from SAXS analyses.

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.

scholarly journals In situ synchrotron X-ray diffraction line-profile analysis of additively manufactured Ti−6Al−4V alloy under tensile deformation

2020 ◽  
Vol 321 ◽  
pp. 03026
Author(s):  
K. Yamanaka ◽  
A. Kuroda ◽  
M. Ito ◽  
M. Mori ◽  
T. Shobu ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Line Profile ◽  
Tensile Deformation ◽  
Profile Analysis ◽  
High Energy ◽  
Line Profile Analysis ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase

In this study, the tensile deformation behavior of an electron beam melted Ti−6Al−4V alloy was examined by in situ X-ray diffraction (XRD) line-profile analysis. The as-built Ti−6Al−4V alloy specimen showed a fine acicular microstructure that was produced through the decomposition of the α′-martensite during the post-melt exposure to high temperatures. Using high-energy synchrotron radiation, XRD line-profile analysis was successfully applied for examining the evolution of dislocation structures not only in the α-matrix but also in the nanosized, low-fraction β-phase precipitates located at the interfaces between the α-laths. The results indicated that the dislocation density was initially higher in the β-phase and an increased dislocation density with increasing applied tensile strain was quantitatively captured in each constitutive phase. It can be thus concluded that the EBM Ti−6Al−4V alloy undergoes a cooperative plastic deformation between the constituent phases in the duplex microstructure. These results also suggested that XRD line-profile analysis combined with highenergy synchrotron XRD measurements can be utilized as a powerful tool for characterizing duplex microstructures in titanium alloys.

In Situ High-Energy X-Ray Diffraction Studies of Melting, Solidification and Solid-State Transformation of Ni3Sn

MRS Advances ◽  
2020 ◽  
Vol 5 (29-30) ◽  
pp. 1529-1535 ◽  
Author(s):  
Rijie Zhao ◽  
Jianrong Gao ◽  
Yang Ren
Keyword(s):  
Solid State ◽  
Elevated Temperatures ◽  
High Energy ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
State Transformation ◽  
Solid State Transformation ◽  
X Ray ◽  
Melting And Solidification

AbstractMelting, solidification and solid-state transformation of the intermetallic Ni3Sn compound were investigated in situ using synchrotron high-energy X-ray diffraction. It was observed that the compound undergoes a hexagonal to cubic transition before melting. In solidification, a disordered cubic phase crystallizes from the liquid at a large undercooling but it is reordered prior to bulk solidification. In melting and solidification, forced or natural flows are active bringing about significant changes of crystal orientations. These in situ observations provided insights into phase transformations of Ni3Sn at elevated temperatures and their roles in formation of metastable microstructure consisting of coarse grains and subgrains.

Diffraction studies of cubic phase stability in undoped zirconia thin films

2000 ◽  
Vol 15 (2) ◽  
pp. 369-376 ◽  
Author(s):  
S. C. Moulzolf ◽  
R. J. Lad
Keyword(s):  
Grain Size ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Electron Cyclotron Resonance ◽  
High Energy ◽  
Electron Beam Evaporation ◽  
Fiber Axis ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Critical Grain Size

Pure stoichiometric ZrO2 films were deposited on amorphous silica substrates by electron beam evaporation of Zr in the presence of an electron cyclotron resonance oxygen plasma. Grain size, strain, and texture were analyzed by x-ray diffraction and reflection high-energy electron diffraction. Films grown at room temperature are polycrystalline and exist in the cubic phase. Growth at elevated temperatures produces coexisting cubic and monoclinic phases and shows a maximum critical grain size of ??~10 nm for stabilization of the cubic phase. Pole figure analysis indicates a preferred cubic [200] fiber axis for room-temperature growth and dual monoclinic {111} and in-plane textures for films grown at 400 °C. Postdeposition annealing experiments confirm the existence of a critical grain size and suggest mechanisms for grain growth.

Stability of Ordered B2-βO and Disordered BCC-β Phases in Tial - A First Principles Study

2021 ◽  
Vol 1016 ◽  
pp. 1159-1165
Author(s):  
Florian Pyczak ◽  
Victoria Kononikhina ◽  
Andreas Stark
Keyword(s):  
First Principles ◽  
Density Functional ◽  
High Energy ◽  
First Principles Calculations ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
Tial Alloys ◽  
Β Phase ◽  
Phase Ordering ◽  
Strength And Ductility

Either at higher temperatures or when a certain alloying element content is exceeded, γ-TiAl alloys contain the β phase (bcc) or its ordered derivate βo (B2). The relatively soft β phase can facilitate hot deformation, but βo is detrimental for creep strength and ductility. Thus, knowledge about βo→β phase transformation is desirable. Surprisingly, even for the binary Ti-Al system it is under discussion whether the ordered βo phase exists. Also, the effect of alloying elements on the β phase ordering is still unclear. In the present work the ordering of the β phase in binary Ti-(39,42,45)Al and ternary Ti-42Al-2X alloys (X=Fe, Cr, Nb, Ta, Mo) which was experimentally investigated by neutron and high energy X-ray diffraction is compared with the results of first principles calculations using density functional theory. Except for Cr the experimentally determined and the predicted behavior correspond.

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.

Structure and Magnetic Properties of MnAl/α-Fe Nano-Composite Powders Prepared by High-Energy Ball Milling

2011 ◽  
Vol 287-290 ◽  
pp. 1492-1495 ◽  
Author(s):  
Hai Xia Wang ◽  
Ping Zhan Si ◽  
Wei Jiang ◽  
Jin Jun Liu ◽  
Jung Goo Lee ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Ball Milling ◽  
Elevated Temperatures ◽  
High Energy ◽  
High Energy Ball Milling ◽  
Composite Powders ◽  
Two Phase ◽  
Nano Composite ◽  
Β Phase ◽  
Energy Ball

Novel nano-composite powders composed of hard-magnetic Mn54Al46 and soft-magnetic α-Fe were prepared by high-energy ball milling. The effect of α-Fe and preparation conditions on the structure and magnetic properties of the composite powders has been investigated. The ε-MnAl transforms to γ-MnAl, τ-MnAl, and β-phase under ball milling and annealing. The saturation magnetization and coercivity of the two-phase samples decrease with increasing temperature for the τ-phase decomposes at elevated temperatures. With increasing iron content, the coercivity decrease first and then increase up to 0.33 T when the Fe content is 10 wt%. Further addition of the magnetically soft iron phase would result in a decrease of the coercivity.

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