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.

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.

Influence of Microstructural Changes in Creep Resistant Steel after Long-Term Creep Tests on the Shape of the Polarization Curves

2015 ◽  
Vol 647 ◽  
pp. 153-161
Author(s):  
Jana Sladká ◽  
Dagmar Jandová ◽  
Eva Chvostová
Keyword(s):  
Martensitic Steel ◽  
Light And Electron Microscopy ◽  
Polarization Curves ◽  
Resistant Steel ◽  
Creep Tests ◽  
Microstructural Changes ◽  
Additional Peak ◽  
Term Creep ◽  
Non Destructive

Creep resistance of the steel depends on chemical and structural composition and structural stability. Therefore it is necessary to check microstructural changes in material during the long-term service, however the necessary material analyses are generally destructive. The submitted contribution describes non-destructive electrochemical method for detection of some microstructural changes taking place during creep exposures. The shape of polarization curves are correlated to the microstructure of CB2 steel, the most promissing (9-12) %Cr martensitic steel for the cast components. The dynamic polarization curves were measured using samples in as received conditions and after long-term creep tests at 650°C. Microstructure was analysed using light and electron microscopy. The microstructure of the CB2 steel changed during creep exposures. In polarization curves additional peak appeared in the main passivation region and the curve shape changed also in the secondary passivation region. The curve changed in dependence on precipitation and growth of Laves phase particles.

The Structure and Stress State of Lamellar Interfaces in Two-Phase Titanium Aluminides

1993 ◽  
Vol 318 ◽  
Author(s):  
Fritz Appel ◽  
Ulrich Christoph ◽  
Richard Wagner
Keyword(s):  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Lattice Mismatch ◽  
Deformation Behaviour ◽  
Lamellar Microstructure ◽  
Misfit Strain ◽  
Shear Stresses ◽  
Dislocation Loops ◽  
Two Phase ◽  
Interfacial Dislocations

ABSTRACTTitanium aluminide alloys with compositions slightly on the Ti-rich side of stoichiometry consist of the intermetallic phases α2 (Ti3Al) and γ(TiAl). The two phases form a lamellar microstructure with various types of coherent and semicoherent interfaces. The lattice mismatch occurring at the semicoherent interfaces is largely accommodated by networks of interfacial dislocations. Nevertheless, a significant homogeneous straining seems to remain at these interfaces, resulting in long-range residual stresses. The present paper reports an electron microscope study of the correlation between the misfit strain of adjacent lamellae and the atomic structure of the interfaces. The residual coherency stresses were determined by analyzing the curvature of dislocation loops which were emitted from the network of the interfacial dislocations. The estimated stresses are close to the shear stresses applied during macroscopic deformation experiments. The effects of these stresses on the deformation behaviour of the material are discussed.

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.

Creep Behaviour and Microstructural Changes of Advanced Creep Resistant Steels after Long-Term Isothermal Ageing

2010 ◽  
Vol 654-656 ◽  
pp. 504-507 ◽  
Author(s):  
Vàclav Sklenička ◽  
Květa Kuchařová ◽  
Milan Svoboda ◽  
A. Kroupa ◽  
J. Čmakal
Keyword(s):  
Rupture Strength ◽  
Creep Behaviour ◽  
Tensile Creep ◽  
Microstructural Stability ◽  
Creep Tests ◽  
Microstructural Changes ◽  
Creep Resistant Steels ◽  
Isothermal Ageing

In this paper we will try to further clarify the creep-strength degradation of selected advanced creep resistant steels. In order to accelerate some microstructural changes and thus to simulate degradation processes in long-term service, isothermal ageing at 650°C for 10000 h was applied to P91, P92 and P23 steels in their as-received states. The accelerated tensile creep tests were performed at temperature 600°C in argon atmosphere on all steels in the as-received state and after long-term isothermal ageing, in an effort to obtain a more complete description of the role of microstructural stability in high temperature creep of these steels. Creep tests were followed by microstructural investigations by means of both transmission and scanning electron microscopy and by the thermodynamic calculations. It is suggested that microstructural instability is the main detrimental process in the long-term degradation of the creep rupture strength of these steels.

Long-Term Creep Modeling of Modified 9Cr-1Mo Steel for a Sodium Cooled Fast Reactor

2010 ◽  
Author(s):  
Woo-Gon Kim ◽  
Jae-Young Park ◽  
Sung-Ho Kim ◽  
Chan-Bock Lee
Keyword(s):  
Constant Load ◽  
Primary Creep ◽  
Least Square ◽  
Creep Data ◽  
Creep Tests ◽  
Omega Method ◽  
Creep Curves ◽  
The Individual ◽  
Term Creep

This paper focused on long-term creep modeling for describing total creep curves of up to rupture for modified 9Cr-1Mo steel (G91). Creep data was obtained by a series of constant-load creep tests at 600°C. Three modified constitutive equations of modified power-law method (MPM), modified theta method (MTM) and modified omega method (MOM), described as a sum of a decaying primary creep and an accelerating tertiary creep, were proposed. A nonlinear least square fitting (NLSF) analysis was carried out on the basis of the creep data so that they provide the best fit to experimental data in optimizing parameter constants of the individual equation. Results of the NLSF analysis showed that in the lower stress regions of 160MPa (σ/σys<0.65), the MTM matched well with the experimental creep data compared with the MPM and MOM, but that in the higher stress regions of 160MPa (σ/σy > 0.65), the MPM revealed better agreement than the MTM and MOM. It was found that the MTM was superior in the modeling of long-term creep curves to the MPM and MOM. Long-term creep curves for the G91 steel were numerically modeled and its creep life was predicted by the MTM.

scholarly journals Primary Creep Behaviour of Two-Phase Titanium Alloy with Various Microstructure

2016 ◽  
Vol 61 (2) ◽  
pp. 683-688
Author(s):  
W. Ziaja ◽  
M. Motyka ◽  
K. Kubiak ◽  
J. Sieniawski
Keyword(s):  
Heat Treatment ◽  
Elevated Temperature ◽  
Creep Behaviour ◽  
Strong Dependence ◽  
Primary Creep ◽  
Fatigue Properties ◽  
Creep Tests ◽  
Two Phase ◽  
Treatment Conditions ◽  
Primary Creep Strain

Abstract Creep and fatigue properties of two-phase titanium alloys show strong dependence on microstructure, especially morphology of the α and β phases which can be controlled to certain extent by proper selection of hot working and heat treatment conditions. In the paper the creep behaviour of Ti-6Al-2Mo-2Cr alloy (VT3-1) at elevated temperature was modelled. Finite element analyses of primary creep stage were carried out taking into account some microstructural features of the two-phase alloy that were included in the physical model and different properties of α and β phases. In order to verify results of calculations distinct types of microstructure were developed in the alloy by heat treatment and creep tests were carried out at elevated temperature (450°C) at various stress levels. Based on the FEM simulations the effect of changes of some microstructure features on primary creep strain development was estimated.

Creep Behavior and Microstructure of XD™ Titanium Aluminide

1990 ◽  
Vol 194 ◽  
Author(s):  
C. R. Feng ◽  
H. H. Smith ◽  
D. J. Michel ◽  
C. R. Crowe
Keyword(s):  
Heat Treatment ◽  
Creep Behavior ◽  
Titanium Aluminide ◽  
Lamellar Structure ◽  
Creep Mechanism ◽  
Creep Testing ◽  
Al Alloy ◽  
Creep Tests ◽  
Two Phase

AbstractThe creep behavior of extruded XD™ Ti-47at%Al/7.5v%TiB2 composite was investigated together with extruded Ti-46at%Al alloy. Prior to creep testing, both materials received a duplex heat-treatment at 1200°C for 16h plus 900°C for 8h. The creep tests were conducted at 69, 103 and 138MPa at 760°C in air. The microstructures of both materials prior to and after the creep testing were examined by TEM. The microstructures suggest that the formation of the TiAl/Ti3Al two-phase lamellar structure was the predominant creep mechanism.

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