Microstructural stability and creep behavior of a lamellar γ-TiAl based alloy with extremely fine lamellar spacing

2002 ◽  
Vol 10 (5) ◽  
pp. 459-466 ◽  
Author(s):  
Wolfram Schillinger ◽  
Helmut Clemens ◽  
Gerhard Dehm ◽  
Arno Bartels
Keyword(s):  
Creep Behavior ◽  
Lamellar Spacing ◽  
Microstructural Stability

Creep Behavior and Microstructural Stability of Lamellar γ-T1AI (Cr, Mo, Si, B) with Extremely Fine Lamellar Spacing

2000 ◽  
Vol 646 ◽  
Author(s):  
Wolfram Schillinger ◽  
Dezhi Zhang ◽  
Gerhard Dehm ◽  
Arno Bartels ◽  
Helmut Clemens
Keyword(s):  
Creep Rate ◽  
Creep Behavior ◽  
Lamellar Microstructure ◽  
Lamellar Spacing ◽  
Primary Creep ◽  
Vacuum Arc ◽  
Internal Stresses ◽  
Microstructural Stability ◽  
Thermodynamical Equilibrium ◽  
Creep Tests

ABSTRACTγ-T1AI (Cr, Mo, Si, B) specimens with two different fine lamellar microstructures were produced by vacuum arc melting followed by a two-stage heat treatment. The average lamellar spacing was determined to be 200 nm and 25–50 nm, respectively. Creep tests at 700°C showed a very strong primary creep for both samples. After annealing for 24 hours at 1000 °C the primary creep for both materials is significantly decreased. The steady-state creep for the specimens with the wider lamellar spacing appears to be similar to the creep behavior prior to annealing while the creep rate of the material with the previously smaller lamellar spacing is significantly higher. Optical microscopy and TEM-studies show that the microstructure of the specimens with the wider lamellar specing is nearly unchanged, whereas the previously finer material was completely recrystallized to a globular microstructure with a low creep resistance. The dissolution of the fine lamellar microstructure was also observed during creep tests at 800 °C as manifested in an acceleration of the creep rate. It is concluded that extremely fine lamellar microstructures come along with a very high dislocation density and internal stresses which causes the observed high primary creep. The microstructure has a composition far away from the thermodynamical equilibrium which leads to a dissolution of the structure even at relatively low temperatures close to the intended operating temperature of γ-T1AI structural parts. As a consequence this limits the benefit of fine lamellar microstructures on the creep behavior.

Creep Behavior and Microstructural Stability of Ti-46Al-9Nb with Different Microstructures

2004 ◽  
Vol 842 ◽  
Author(s):  
S. Bystrzanowski ◽  
A. Bartels ◽  
H. Clemens ◽  
R. Gerling ◽  
F.-P. Schimansky ◽  
...  
Keyword(s):  
Creep Behavior ◽  
Sheet Material ◽  
Lamellar Microstructure ◽  
Lamellar Spacing ◽  
Activation Energies ◽  
Microstructural Stability ◽  
X Ray Diffraction ◽  
Creep Tests ◽  
Apparent Activation Energies ◽  
Term Creep

ABSTRACTIn this paper the creep behavior and the microstructural stability of Ti-46Al-9Nb (in at.%) sheet material were investigated in the temperature range of 700°C to 815°C. The study involves three different types of microstructure, namely fully lamellar with narrow lamellar spacing, duplex and massively transformed. Short-term creep experiments conducted at 700°C and 225 MPa confirmed that the lamellar microstructure with narrow lamellar spacing exhibits a much higher creep resistance when compared to the massively transformed and duplex ones. During longterm creep tests up to 1500 hours stress exponents (in the range of 4.4 to 5.8) and apparent activation energies (of about 4 eV) have been estimated by means of load and temperature changes, respectively. Both, stress exponents and activation energies suggest that under the applied conditions diffusion-assisted climb of dislocations is the dominant creep mechanism. The thermal stability of the different microstructures under various creep conditions has been analyzed by electron microscopy and X-ray diffraction. Our investigations revealed considerable stress and temperature induced microstructural changes which are reflected in the dissolution of the α2 phase accompanied by precipitation of a Ti/Nb - rich phase situated at grain boundaries. This phase was identified as a ω-related phase with B82-type structure. It was shown, that in particular the duplex microstructure is prone to such microstructural instabilities.

The effect of lamellar spacing on the creep behavior of a fully lamellar TiAl alloy

2000 ◽  
Vol 8 (5-6) ◽  
pp. 525-529 ◽  
Author(s):  
C.E. Wen ◽  
K. Yasue ◽  
J.G. Lin ◽  
Y.G. Zhang ◽  
C.Q. Chen
Keyword(s):  
Creep Behavior ◽  
Tial Alloy ◽  
Lamellar Spacing ◽  
Fully Lamellar

The Creep Behaviors of Two Fine-grained XD TiAl Alloys Produced by Similar Heat Treatments

2004 ◽  
Vol 842 ◽  
Author(s):  
Hanliang Zhu ◽  
Dongyi Seo ◽  
Kouichi Maruyama ◽  
Peter Au
Keyword(s):  
Grain Boundaries ◽  
Creep Resistance ◽  
Lamellar Spacing ◽  
Heat Treatments ◽  
Tensile Creep ◽  
Microstructural Stability ◽  
Creep Tests ◽  
Tial Alloys ◽  
Fine Grained ◽  
Interlocked Grain

ABSTRACTThe microstructural characteristics and creep behavior of two fine-grained XD TiAl alloys, Ti-45Al and 47Al–2Nb–2Mn+0.8vol%TiB2 (at%), were investigated. A nearly lamellar structure (NL) and two kinds of fully lamellar (FL) structures in both alloys were prepared by selected heat treatments. The results of microstructural examination and tensile creep tests indicate that the 45XD alloy with a NL structure possesses an inferior creep resistance due to its coarse lamellar spacing and larger amount of equiaxed γ grains at the grain boundaries, whereas the same alloy in a FL condition with fine lamellar spacing lowers the minimum creep rates. Contrary to 45XD, the 47XD alloy with a NL structure exhibits the best creep resistance. However, 47XD with a FL structure with finer lamellar spacing shows inferior creep resistance. On the basis of microstructural deformation characteristics, it is suggested that the well-interlocked grain boundary and relatively coarse colony size in FL and NL 47XD inhibit sliding and microstructural degradation at the grain boundaries during creep deformation, resulting in better creep resistance. Therefore, good microstructural stability is essential for improving the creep resistance of these alloys.

Microstructural Stability and Creep Behavior of Directionally Solidified MgAl2O4/Y3Al5O12 Eutectic Composite

2015 ◽  
Vol 752-753 ◽  
pp. 189-193 ◽  
Author(s):  
Serkan Abali
Keyword(s):  
High Temperature ◽  
Creep Behavior ◽  
Creep Strength ◽  
Dislocation Motion ◽  
Microstructural Stability ◽  
Directionally Solidified ◽  
Compressive Creep ◽  
Transmission Electron ◽  
Creep Characteristics ◽  
Mechanisms Of Deformation

In the present work, compressive creep characteristics of directionally solidified MAS-YAG (MgAl2O4/Y3Al5O12) were investigated at high temperature. The compressive creep strength of a crystal grown at a rate of 5 mm/min and a flow rate of 1.2 mm/min at 1500 °C under a strain rate of 1.0 × 10-4 was only 400 MPa, which is slightly higher than that of crystals grown under different conditions. The compressive creep strength of an oxide eutectic fabricated by the directional solidification method is higher than that of a polycrystalline sintered eutectic with the same composition. The creep behavior at high temperature was studied and the mechanisms of deformation by dislocation motion were revealed by Transmission Electron Microscopy (TEM) observations.

Advanced intermetallic γ-TiAl based alloys with improved microstructural stability during creep

2014 ◽  
Vol 1760 ◽  
Author(s):  
M. Kastenhuber ◽  
B. Rashkova ◽  
H. Clemens ◽  
S. Mayer
Keyword(s):  
Discontinuous Precipitation ◽  
Lamellar Spacing ◽  
Precipitation Process ◽  
Nominal Composition ◽  
Microstructural Stability ◽  
Creep Tests ◽  
Creep Properties ◽  
High Temperature Materials ◽  
Step Heat Treatment ◽  
Kinetics Of

ABSTRACTEnsuring microstructural stability under technical relevant conditions is a determining criterion for the development of innovative high-temperature materials. In this work, the influ-ence of C and Si on the microstructural stability during creep exposure was investigated for a β-solidifying γ-TiAl based alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at.%), named TNM. With a two-step heat treatment a microstructure consisting of fine lamellar α2/γ-colonies, surrounded by βo-phase and areas of discontinuous precipitation, starting from the boundaries of the lamellar colonies, was adjusted. Creep tests were carried out to examine the potential of C and Si to prevent microstructural instability during creep and hence improving the creep properties. At 815 °C the discontinuous precipitation process of the TNM alloy continues during ensuing creep testing leading to a reduced creep resistance. In comparison, the minimum creep rate of the TNM-0.3C-0.3Si alloy was significantly decreased caused by the lower βo-phase content and average lamellar spacing within the α2/γ-colonies, the precipitation of p-Ti3AlC carbides and the retarded kinetics of discontinuous precipitation.

Creep behavior and microstructural stability of Al-Cu-Mg-Ag and Al-Cu-Li-Mg-Ag alloys

1997 ◽  
Vol 234-236 ◽  
pp. 571-574 ◽  
Author(s):  
Susan M. Kazanjian ◽  
Ning Wang ◽  
Edgar A. Starke
Keyword(s):  
Creep Behavior ◽  
Microstructural Stability
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