Stress Driven Phase Transformations and Recrystallization Processes in Two-Phase Titanium Aluminide Alloys

2000 ◽  
Vol 652 ◽  
Author(s):  
Fritz Appel ◽  
Michael Oehring
Keyword(s):  
Phase Transformation ◽  
Titanium Aluminide ◽  
Electron Microscope Study ◽  
Phase Boundaries ◽  
Two Phase ◽  
Titanium Aluminide Alloy ◽  
Lower Solubility ◽  
Term Creep ◽  
Titanium Aluminide Alloys

ABSTRACTThe paper presents an electron microscope study of phase transformation and recrystallization in an intermetallic α2(Ti3Al) + γ(TiAl) titanium aluminide alloy, after long-term creep. The mechanisms are closely related to the atomic structure of the α2/γ phase boundaries and are probably driven by a non-equilibrium of the phase composition leading to the dissolution of the α2 phase. The α2 /γ transformation is accompanied by the formation of precipitates, because the γ(TiAl)phase has a significantly lower solubility for interstitial impurities than the α2(Ti3Al) phase.

Point Defect Mechanisms in Deformation and Phase Transformation of Titanium Aluminide Alloys

2002 ◽  
Vol 753 ◽  
Author(s):  
Fritz Appel ◽  
Jonathan D.H. Paul ◽  
Ulrich Fröbel
Keyword(s):  
Phase Transformation ◽  
Point Defects ◽  
Titanium Aluminide ◽  
High Resolution Electron Microscopy ◽  
Transport Processes ◽  
Two Phase ◽  
Structural Characterisation ◽  
Resolution Electron ◽  
Term Creep ◽  
Titanium Aluminide Alloys

ABSTRACTPoint defects in intermetallic compounds are subjected to significant constraints due to the directional bonding, long-range order and off-stoichiometric deviation of the materials. This leads to a variety of defects with distinct differences in morphology, concentration and mobility. In the present study the implications of these defect characteristics on the mechanical properties of two-phase titanium aluminide alloys will be investigated. The major areas of the study are: (i) deformation induced point defects that contribute to work hardening; (ii) dislocation locking due to the formation of defect atmospheres; (iii) transport processes involved in phase transformation and recrystallization occurring during long-term creep. The applied methods include mechanical testing, static strain aging and structural characterisation by high resolution electron microscopy.

Tensile and Creep Behavior of Ordered Orthorhombic Ti2A1Nb-Based Alloys

1990 ◽  
Vol 213 ◽  
Author(s):  
R.G. Rowe ◽  
D.G. Konitzer ◽  
A.P. Woodfield ◽  
J.C. Chesnutt
Keyword(s):  
Heat Treatment ◽  
Titanium Aluminide ◽  
Room Temperature ◽  
Single Phase ◽  
Two Phase ◽  
Creep Properties ◽  
Specific Strength ◽  
Heat Treated ◽  
Titanium Aluminide Alloys

ABSTRACTTitanium aluminide alloys with compositions near Ti-25A1-25Nb at.% were prepared by both rapid solidification and ingot techniques. Their tensile and creep properties were studied after heat treatment to produce various microstructures containing ordered orthorhombic (O) [1], ordered beta (βo), and α2 phases. It was found that these alloys had higher specific strength from room temperature to 760°C than conventional α2 alloys. Ductility and tensile strength of O+βo alloys were strongly dependent upon heat treatment, with the highest strength observed as-heat-treated, and the highest ductility after long term aging. The creep resistance of single phase O and two phase O+βo alloys was strongly dependent upon heat treatment.

Evolution of hot rolling texture in β (B2)-phase of a two-phase (O+B2) titanium–aluminide alloy

2008 ◽  
Vol 483-484 ◽  
pp. 551-554 ◽  
Author(s):  
S.R. Dey ◽  
Satyam Suwas ◽  
J.-J. Fundenberger ◽  
J.X. Zou ◽  
T. Grosdidier ◽  
...  
Keyword(s):  
Hot Rolling ◽  
Titanium Aluminide ◽  
Rolling Texture ◽  
Two Phase ◽  
Titanium Aluminide Alloy ◽  
B2 Phase

Microstructure and interfaces in TiB2/Ti-46Al-3Cr Alloy Composites

1995 ◽  
Vol 410 ◽  
Author(s):  
Weimin Si ◽  
Michael Dudley ◽  
Pengxing Li ◽  
Renjie Wu
Keyword(s):  
Electron Microscopy ◽  
Titanium Aluminide ◽  
Analytical Electron Microscopy ◽  
Lattice Misfit ◽  
High Resolution Electron Microscopy ◽  
Amorphous Layer ◽  
Two Phase ◽  
Titanium Aluminide Alloy ◽  
Resolution Electron ◽  
Crystallographic Orientation Relationship

ABSTRACTA ternary titanium aluminide alloy, Ti-46Al-3Cr (at%), was discontinuously reinforced with 5 vol% titanium diboride (TiB2), by an in-situ synthesis technique, resulting in a two phase γ(TiAl) (mainly) and α2(Ti3Al) matrix with randomly dispersed TiB2 particle. Interfaces of TiB2-TiAl were investigated by Analytical Electron Microscopy (AEM) and High Resolution Electron Microscopy (HREM). No consistent crystallographic orientation relationship was observed between TiB2 particle and TiAl matrix, and there was no evidence of alloying elements (such as Cr) segregation or interphase formation at the TiB2-TiAl interface. HREM results indicated that no semi-coherent interface between TiB2 and TiAl has been observed. There existed a thin amorphous layer (0.5 to 1.3 nm) at the TiB2-TiAl interface, which may accommodate the large lattice misfit across the interface and enhance the interfacial bonding.

Creep Deformation of a Fully Lamellar Gamma Based Titanium Aluminide Alloy

1996 ◽  
Vol 460 ◽  
Author(s):  
F. Herrouin ◽  
P. Bowen ◽  
I. P. Jones
Keyword(s):  
Gas Turbine ◽  
Creep Deformation ◽  
Titanium Aluminide ◽  
Creep Resistance ◽  
Tial Alloy ◽  
Operating Conditions ◽  
Two Phase ◽  
Titanium Aluminide Alloy ◽  
Aero Engine ◽  
Fully Lamellar

ABSTRACTA complex two phase γ-TiAl alloy, Ti-47Al-lCr-1Mn-2Ta-0.2Si (at.%) in a fully lamellar condition, has been creep tested at a stress of 200MPa and a temperature of 700°C. This simulates the in-service operating conditions for several potential gas turbine aero engine applications where creep resistance is a design limiting material property. The results have indicate that reduction in lamellae thickness and avoidance of feathery type microstructures contribute to improved creep resistance.

Recent Advances in Gamma Titanium Aluminide Alloys

1990 ◽  
Vol 213 ◽  
Author(s):  
Young-Won (Y-W.) Kim
Keyword(s):  
Titanium Aluminide ◽  
Thin Plates ◽  
Second Phase ◽  
Two Phase ◽  
Gamma Titanium Aluminide ◽  
Gamma Titanium ◽  
The Matrix ◽  
Evolution Of Microstructure ◽  
Titanium Aluminide Alloys ◽  
Extended Discussion

ABSTRACTGamma titanium aluminide alloys of current interest are two-phase alloys consisting of γ-TiAl phase as the matrix and a α2-Ti3Al phase as the second phase. The properties of these alloys depend on alloy composition, processing, microstructure, and their combination. Two major microstructural constituents are gamma grains and lamellar grains, the latter of which contain alternate layers of gamma (γ) and alpha-2 (α2) thin plates. The relative amounts and distribution of these two constituents are the main factors controlling mechanical properties. This paper reviews our current understanding of the composition/microstructure/property relationships. An extended discussion will be made on the fundamental aspects of the formation of lamellar structure during cooling and the evolution of microstructure occurring during thermomechanical treatments.

Microstructural Changes During Long-Term Tension Creep of Two-Phase γ-Titanium Aluminide Alloys

1996 ◽  
Vol 460 ◽  
Author(s):  
M. Oehring ◽  
P. J. Ennis ◽  
F. Appel ◽  
R. Wagner
Keyword(s):  
Titanium Aluminide ◽  
Primary Creep ◽  
Creep Tests ◽  
Two Phase ◽  
Microstructural Changes ◽  
Deformation Processes ◽  
Interfacial Dislocations ◽  
Structural Parts ◽  
Heterogeneous Formation

ABSTRACTLong-term tension creep tests were performed on a Ti-48 at.% Al-2 at.% Cr alloy in order to assess the material behaviour under the intended service conditions for structural parts in turbine engines. Deformation processes and microstructural changes were investigated by TEM on a specimen loaded to 140 MPa for 5988 h at 700 °C. At lamellar boundaries the emission of interfacial dislocations was observed and is thought to contribute significantly to the high primary creep rate of the material. Under the creep conditions gliding dislocations apparently become locked by the heterogeneous formation of precipitates along their cores. Lamellar interfaces revealed ledges which indicates that they migrate during creep.

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