Static and Dynamic Strain Ageing in Two-Phase Gamma Titanium Aluminides

2000 ◽  
Vol 646 ◽  
Author(s):  
U. Christoph ◽  
F. Appel
Keyword(s):  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Deformation Behaviour ◽  
Dynamic Strain ◽  
Dynamic Strain Ageing ◽  
Two Phase ◽  
Fast Kinetics ◽  
Strain Ageing ◽  
Wide Range ◽  
Dislocation Pinning

ABSTRACTThe deformation behaviour of two-phase titanium aluminides was investigated in the intermediate temperature interval 450–750 K where the Portevin-LeChatelier effect occurs. The effect has been studied by static strain ageing experiments. A wide range of alloy compositions was investigated to identify the relevant defect species. Accordingly, dislocation pinning occurs with fast kinetics and is characterized by a relatively small activation energy of 0.7 eV, which is not consistent with a conventional diffusion process. Furthermore, the strain ageing phenomena are most pronounced in Ti-rich alloys. This gives rise to the speculation that antisite defects are involved in the pinning process. The implications of the ageing processes on the deformation behaviour of two-phase titanium aluminide alloys will be discussed.

Investigation of Dynamic Strain Ageing Effects of Low Alloy Steels 15Kh2MFA and 15Kh2NMFA

2005 ◽  
Vol 482 ◽  
pp. 367-370
Author(s):  
Miroslava Ernestová
Keyword(s):  
Strain Rate ◽  
Tensile Tests ◽  
Dynamic Strain ◽  
Low Alloy Steels ◽  
Strain Rates ◽  
Dynamic Strain Ageing ◽  
Strain Ageing ◽  
Lower Strain ◽  
Wide Range ◽  
Alloy Steels

The paper summarizes results of tensile tests in low alloy steel (LAS) specimens (steels 15Kh2MFA and 15Kh2NMFA). Slow Strain Rate Tensile tests (SSRT) were performed in air at temperatures from 22 to 325°C over a wide range of strain rates from 2.5×10-6 to 1.67×10-3 s-1. The possible effect of strain rate and temperature to mechanical properties of tested LAS is searched for. The dynamic strain ageing (DSA) was observed within certain temperature ranges at lower strain rates tested and its hardening effect in terms of the maximum strengthening stress decreased linearly with the increase of log strain rate. It has been found that the occurrence of susceptibility to environmentally assisted cracking (EAC) of tested steels in high temperature water (HTW) is corelated to the DSA behavior. The result suggest that DSA reduces ductility of reactor pressure vessel (RPV) steel and its role in enhancing the EAC of RPV steels should not be neglected, in view of the coincidence with susceptibility zones for DSA and EAC in terms of strain rate and temperature. A reasonable coincidence was observed between the susceptibility to DSA exhibited by SSRT in air and with the EAC behavior observed in laboratory experiments.

High Temperature Stress-Strain Properties of a Low-Carbon Steel from Hot Machining Tests

1973 ◽  
Vol 187 (1) ◽  
pp. 263-272 ◽  
Author(s):  
M. G. Stevenson ◽  
P. L. B. Oxley
Keyword(s):  
Cutting Speed ◽  
Machining Process ◽  
Dynamic Strain ◽  
Low Carbon ◽  
Dynamic Strain Ageing ◽  
Stress Strain ◽  
Strain Ageing ◽  
Wide Range ◽  
Hot Machining ◽  
Conventional Machining

Machining tests are described in which the cutting speed is kept constant and the primary shear zone temperature varied through a wide range by preheating the workpiece. Variations of the constants σ1 and n of the assumed stress-strain equation σ = σ1 εn with temperature, for an estimated strain rate of 900/s, are obtained. These show a range of temperature in which dynamic strain ageing takes place. This is consistent with results of conventional machining tests on the same material in which dynamic strain ageing takes place in the secondary zone in a certain speed range. Implications of the results for the machining process are discussed and explanations suggested for variation of force with speed in conventional machining and force with temperature in hot machining.

Static and Dynamic Strain Aging in Two-Phase γ-Titanium Aluminides

1996 ◽  
Vol 460 ◽  
Author(s):  
U. Christoph ◽  
F. Appel ◽  
R. Wagner
Keyword(s):  
Mechanical Properties ◽  
Activation Energy ◽  
Strain Aging ◽  
Titanium Aluminides ◽  
Rate Sensitivity ◽  
Dynamic Interaction ◽  
Dynamic Strain ◽  
Two Phase ◽  
Fast Kinetics ◽  
Negative Strain Rate Sensitivity

ABSTRACTDeformation of two-phase titanium aluminides exhibits discontinuous yielding and a negative strain rate sensitivity over the temperature range 450–750 K. These phenomena are usually associated with the Portevin-LeChatelier effect which is due to the dynamic interaction of diffusing defects with the dislocations. The resulting glide resistance was investigated by static strain aging. The experiments involve the prestraining of samples followed by aging under a relaxing load for certain periods of time. Reloading of the samples resulted in distinct yield points. The investigations were performed on two-phase γ-titanium aluminides having different compositions and microstructures which are currently being considered for technical applications. Accordingly, dislocation locking occurs with fast kinetics which is characterized by a low activation energy. The experimental results will be discussed with respect to the nature of the diffusional mechanism and possible implication on the mechanical properties of the materials.

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.

Interactions of Dislocations and Deformation Twins with Interfacial Boundaries in Titanium Aluminides

1993 ◽  
Vol 319 ◽  
Author(s):  
Fritz Appel ◽  
Richard Wagner
Keyword(s):  
Shear Deformation ◽  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Deformation Behaviour ◽  
Lamellar Microstructure ◽  
High Resolution Electron Microscopy ◽  
Misfit Dislocations ◽  
Two Phase ◽  
Deformation Twins ◽  
Resolution Electron

AbstractThe deformation behaviour of two-phase titanium aluminide alloys with a lamellar microstructure of the intermetallic phases α2(Ti3Al) and y(TiAl) was studied. The interaction processes of dislocations and deformation twins, respectively, with the lamellar interfaces are investigated by conventional and high-resolution electron microscopy. The mechanisms of translation of shear deformation across, the lamellar boundaries depend on their structure. Semicoherent interfaces are very effective barriers limiting the propagation of shear deformation. The misfit dislocations present at these interfaces support, on the other hand, the generation of dislocations and deformation twins. The observed processes are discussed regarding plastic deformation and crack propagation in the material.

High Temperature Stress-Strain Properties of a Low-Carbon Steel from Hot Machining Tests

1973 ◽  
Vol 187 (1) ◽  
pp. 263-272 ◽  
Author(s):  
M. G. Stevenson ◽  
P. L. B. Oxley
Keyword(s):  
Cutting Speed ◽  
Machining Process ◽  
Dynamic Strain ◽  
Low Carbon ◽  
Dynamic Strain Ageing ◽  
Stress Strain ◽  
Strain Ageing ◽  
Wide Range ◽  
Hot Machining ◽  
Conventional Machining

Machining tests are described in which the cutting speed is kept constant and the primary shear zone temperature varied through a wide range by preheating the workpiece. Variations of the constants σ1 and n of the assumed stress-strain equation σ = σ1 εn with temperature, for an estimated strain rate of 900/s, are obtained. These show a range of temperature in which dynamic strain ageing takes place. This is consistent with results of conventional machining tests on the same material in which dynamic strain ageing takes place in the secondary zone in a certain speed range. Implications of the results for the machining process are discussed and explanations suggested for variation of force with speed in conventional machining and force with temperature in hot machining.

Dynamic strain ageing and crack propagation in the 2091 AlLi alloy

1993 ◽  
Vol 29 (11) ◽  
pp. 1379-1384 ◽  
Author(s):  
D. Delafosse ◽  
G. Lapasset ◽  
L.P. Kubin
Keyword(s):  
Crack Propagation ◽  
Dynamic Strain ◽  
Dynamic Strain Ageing ◽  
Strain Ageing

Recent Advances in Development and Processing of Titanium Aluminide Alloys

2000 ◽  
Vol 646 ◽  
Author(s):  
Fritz Appel ◽  
Helmut Clemens ◽  
Michael Oehring
Keyword(s):  
High Temperature ◽  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Environmental Stability ◽  
Physical Metallurgy ◽  
Specific Strength ◽  
Wide Range ◽  
Structural Applications ◽  
Strength And Stiffness ◽  
Nickel Base

ABSTRACTIntermetallic titanium aluminides are one of the few classes of emerging materials that have the potential to be used in demanding high-temperature structural applications whenever specific strength and stiffness are of major concern. However, in order to effectively replace the heavier nickel-base superalloys currently in use, titanium aluminides must combine a wide range of mechanical property capabilities. Advanced alloy designs are tailored for strength, toughness, creep resistance, and environmental stability. Some of these concerns are addressed in the present paper through specific comments on the physical metallurgy and technology of gamma TiAl-base alloys. Particular emphasis is placed on recent developments of TiAl alloys with enhanced high-temperature capability.

Intergranular Stress Development in Al during Dynamic Strain Ageing

2004 ◽  
Vol 12 (1-3) ◽  
pp. 213-217 ◽  
Author(s):  
M.R. Daymond ◽  
E.C. Oliver
Keyword(s):  
Dynamic Strain ◽  
Dynamic Strain Ageing ◽  
Strain Ageing ◽  
Stress Development
Sign in / Sign up

Export Citation Format

Share Document