Creep Properties of a High Niobium Containing γ-TiAl Alloy Sheet Material

2002 ◽  
Vol 753 ◽  
Author(s):  
A. Bartels ◽  
S. Bystrzanowski ◽  
R. Gerling ◽  
F.-P. Schimansky ◽  
H. Kestler ◽  
...  
Keyword(s):  
Activation Energy ◽  
Stress Exponent ◽  
Elevated Temperatures ◽  
Sheet Material ◽  
Rolling Direction ◽  
Constant Load ◽  
Alloy Sheet ◽  
Tensile Creep ◽  
Creep Tests ◽  
Fine Grained

ABSTRACTIn this study Ti-46Al-9Nb (at%) sheet material processed by a powder metallurgical route was examined. Subsequent to hot rolling the sheets were subjected to a stress-relief treatment at 1273K for 3 hours. During this heat treatment a fine-grained near gamma microstructure has been formed. 100 hours tensile creep tests under constant load were carried out at 700°C in rolling direction, transverse direction as well as 45° direction. Using the method of load changes a stress exponent of 4.1 was determined. Furthermore, the apparent activation energy was determined in the temperature range of 715 – 775°C. Both stress exponent and activation energy suggest that diffusion assisted dislocation climb is the dominant creep mode. A comparison of these results with those of so-called conventional or so-called “2nd generation” γ-TiAl based alloys, e.g. Ti-46.5Al-4(Cr,Nb,Ta,B) (at%) and Ti-47Al-4(Cr,Mn,Nb,Si,B) (at%), indicates a significantly better creep resistance and a higher activation energy of the high Nb containing alloy. Additionally, internal friction experiments were conducted in order to analyze the deformation behavior under very small strains at elevated temperatures.

Impression creep of lead

1994 ◽  
Vol 9 (4) ◽  
pp. 903-908 ◽  
Author(s):  
Donyau Chiang ◽  
J. C. M. Li
Keyword(s):  
Creep Test ◽  
Elevated Temperatures ◽  
Constant Load ◽  
Constant Stress ◽  
Tensile Creep ◽  
Indentation Creep ◽  
Impression Creep ◽  
Creep Tests ◽  
Creep Measurements ◽  
Cylindrical Punch

The impression creep behavior of lead was investigated using a 100 μm diameter punch at ambient and elevated temperatures (433 K-563 K) under punching stresses of 6–70 MPa. The results were compared with the data obtained from conventional creep tests reported in the literature. Unlike the indentation creep test, the impression creep test showed a steady-state velocity after a short transient period when the flat-end cylindrical punch was pushed against the lead surface by a constant load. Both the temperature and stress dependences were comparable to those of the constant stress tensile creep tests under similar conditions. A master curve for lead was established by collecting data from the impression creep tests and the constant stress tensile creep tests. The indentation creep measurements for lead were included also. However, the indentation data depend on the load applied.

Improved Formability and Deep Drawing of Cross-Rolled Magnesium Alloy Sheets at Elevated Temperatures

2005 ◽  
Vol 488-489 ◽  
pp. 461-464 ◽  
Author(s):  
Yong Chao Xu ◽  
Shi Hong Zhang ◽  
H.M. Liu ◽  
Z.T. Wang ◽  
W.T. Zheng ◽  
...  
Keyword(s):  
Magnesium Alloy ◽  
Deep Drawing ◽  
Elevated Temperatures ◽  
Rolling Direction ◽  
Alloy Sheet ◽  
Rolled Sheet ◽  
Drawing Ratio ◽  
Cross Rolling ◽  
Magnesium Alloy Sheet ◽  
Cylindrical Cup

The extruded sheets were prepared at the temperature between 350ıand 400ı, and the magnesium alloy sheet was manufactured by a new method, cross rolling, in which the rolling direction was changed in each pass. At the time, deep drawing of magnesium alloy sheet was investigated at elevated temperatures. The results show that the sheet has refined-grain by cross-rolling after it was annealed at 250ı, and the formability is significantly improved at lower temperatures, which is superior to the extruded sheet and the one-way rolled sheet. Deep drawing of magnesium alloy was performed successfully, and cylindrical cup of limited drawing ratio (LDR) 2.6 and 35 mm deep rectangular box (65ı50) was achieved at the lower temperature of 170ı. The different types of fracture were analyzed and reasonable parameters were determined.

An investigation of the creep processes in tin and aluminum using a depth-sensing indentation technique

1992 ◽  
Vol 7 (3) ◽  
pp. 627-638 ◽  
Author(s):  
V. Raman ◽  
R. Berriche
Keyword(s):  
Stress Exponent ◽  
Constant Load ◽  
Indentation Creep ◽  
Depth Sensing ◽  
Creep Tests ◽  
Si Substrates ◽  
Uniaxial Creep ◽  
Rate Versus ◽  
Deformation Properties ◽  
Film Substrate

Constant load creep experiments were conducted using a depth-sensing indentation instrument with indentation depths in the submicron range. Experiments were conducted on polycrystalline Sn and sputtered Al films on Si substrates. The results show that the plastic depth versus time curves and the strain rate versus stress plots from these experiments are analogous to those obtained from conventional creep experiments using bulk specimens. The value of the stress exponent for Sn is close to the reported values from uniaxial creep tests. Tests on Al films showed that the stress exponent is dependent on the indentation depth and is governed by the proximity to the film/substrate interface. Load change experiments were also performed and the data from these tests were analyzed. It is concluded that indentation creep experiments may be useful in elucidating the deformation properties of materials and in identifying deformation mechanisms.

Compressive properties at elevated temperatures of porous aluminum processed by the spacer method

2005 ◽  
Vol 20 (12) ◽  
pp. 3385-3390 ◽  
Author(s):  
Masataka Hakamada ◽  
Tatsuho Nomura ◽  
Yasuo Yamada ◽  
Yasumasa Chino ◽  
Hiroyuki Hosokawa ◽  
...  
Keyword(s):  
Activation Energy ◽  
Relative Density ◽  
Stress Exponent ◽  
Elevated Temperatures ◽  
Chemical Compositions ◽  
Compressive Properties ◽  
Homogeneous Microstructure ◽  
Plateau Stress ◽  
Porous Aluminum

Compressive properties at 573–773 K of porous aluminum produced by the spacer method were investigated and compared with those of bulk reference aluminum with the same chemical compositions. The stress exponent and activation energy for deformation at elevated temperatures in the porous aluminum were in agreement with those in the bulk reference aluminum. In addition, the plateau stress of the porous aluminum was comparable to the stress of the bulk reference aluminum upon compensation by the relative density. Therefore, it is conclusively demonstrated that the mechanism of deformation at elevated temperatures in the porous aluminum is the same as that in the bulk reference aluminum. This is likely due to the homogeneous microstructure in the porous aluminum produced by the spacer method.

scholarly journals Nanoindentation Studies of Plasticity and Dislocation Creep in Halite

Geosciences ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 79 ◽  
Author(s):  
Christopher Thom ◽  
David Goldsby
Keyword(s):  
Strain Rate ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Constant Load ◽  
Dislocation Creep ◽  
Indentation Creep ◽  
Creep Tests ◽  
Creep Flow ◽  
A Value ◽  
Flow Laws

Previous deformation experiments on halite have collectively explored different creep mechanisms, including dislocation creep and pressure solution. Here, we use an alternative to conventional uniaxial or triaxial deformation experiments—nanoindentation tests—to measure the hardness and creep behavior of single crystals of halite at room temperature. The hardness tests reveal two key phenomena: (1) strain rate-dependent hardness characterized by a value of the stress exponent of ~25, and (2) an indentation size effect, whereby hardness decreases with increasing size of the indents. Indentation creep tests were performed for hold times ranging from 3600 to 106 s, with a constant load of 100 mN. For hold times longer than 3 × 104 s, a transition from plasticity to power-law creep is observed as the stress decreases during the hold, with the latter characterized by a value of the stress exponent of 4.87 ± 0.91. An existing theoretical analysis allows us to directly compare our indentation creep data with dislocation creep flow laws for halite derived from triaxial experiments on polycrystalline samples. Using this analysis, we show an excellent agreement between our data and the flow laws, with the strain rate at a given stress varying by less than 5% for a commonly used flow law. Our results underscore the utility of using nanoindentation as an alternative to more conventional methods to measure the creep behavior of geological materials.

Tensile and Creep Properties of the Refractory Nb Base In-Situ Composite

2003 ◽  
Vol 17 (08n09) ◽  
pp. 1608-1614
Author(s):  
Jin Hak Kim ◽  
Tatsuo Tabaru ◽  
Hisatoshi Hirai
Keyword(s):  
Fracture Surface ◽  
Tensile Tests ◽  
Constant Load ◽  
Tensile Creep ◽  
Tensile Fracture ◽  
Creep Tests ◽  
Tensile Fracture Surface ◽  
In Situ Composite ◽  
Temperature Ranges

Niobium-base in-situ composite Nb-18Si-5Mo-5Hf-2C (in mol%) was prepared and heat-treated at 2070 K for 20 hour. The uni-axile tensile tests at high temperature ranges and the constant load tensile creep tests at 1570 K were performed. The specimen tensile-tested at 1470 K exhibited the excellent UTS of 450 MPa, and the brittle to ductile transition temperature is between 1470 and 1670 K. The specimens creep tested showed good creep strength; the stress exponent is about 5. The tensile fracture surface of the in-situ composite is complex and attributed to cleavage of the Nb 5 Si 3, Nb ss / Nb 5 Si 3 interface separation, ductile rupture of the Nb ss and correlations of these. On the otherhand, the fracture surface of creep tested consists of intergranular above 150 MPa and transgranular below 120 MPa with severely deformed Nb ss .

Effect of Long-Term Aging and Creep Exposure on the Microstructure of TiAl-Based Alloy for Industrial Applications

2004 ◽  
Vol 842 ◽  
Author(s):  
Juraj Lapin ◽  
Mohamed Nazmy ◽  
Marc Staubli
Keyword(s):  
Chemical Composition ◽  
Constant Load ◽  
Industrial Applications ◽  
Tensile Creep ◽  
Creep Tests ◽  
Fine Needle ◽  
Term Creep ◽  
Applied Stresses ◽  
Creep Exposure

ABSTRACTThe effect of long-term aging and creep exposure on the microstructure of a cast TiAl-based alloy with nominal chemical composition Ti-46Al-2W-0.5Si (at.%) was studied. The aging experiments were performed at temperatures between 973 and 1073 K for various times ranging from 10 to 14000 h in air. Constant load tensile creep tests were performed at applied stresses ranging from 150 to 400 MPa and at temperatures between 973 and 1123 K up to 25677 h. During aging and creep testing the α2(Ti3Al)-phase in the lamellar and feathery regions transforms to the γ(TiAl)-phase and fine needle-like B2 precipitates. Microstructural instabilities lead to a softening of the alloy. The effect of this softening on long-term creep resistance is negligible at temperatures of 973 and 1023 K.

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.

Stress-Induced Change of the Microstructure and Strength of Modified 9Cr-1Mo Steel Under Fatigue and Creep Loadings at Elevated Temperatures

2017 ◽  
Author(s):  
Taichi Shinozaki ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Activation Energy ◽  
Applied Stress ◽  
Test Temperature ◽  
Elevated Temperatures ◽  
Critical Value ◽  
Atomic Diffusion ◽  
Dominant Factor ◽  
Martensitic Structure ◽  
Creep Tests ◽  
Microstructure Change

The change of the lath martensitic structure in modified 9Cr-1Mo steel was observed in the specimens after the fatigue and creep tests using EBSD (Electron Back-Scatter Diffraction). The Kernel Average Misorientation (KAM) value obtained from the EBSD analysis were used for the quantitative evaluation of the change in the lath martensitic texture. It was found that the average KAM values of the fractured specimens decreased clearly after 107−108 cycles of the fatigue loading at temperatures higher than 500°C when the amplitude of the applied stress exceeded a critical value. This change corresponded to the disappearance of the lath martensitic structure. The critical value decreased monotonically with the increase of the test temperature. This microstructure change decreased the strength of the alloy drastically. It was found that the change of the microstructure started at a certain time at each test temperature as a function of the amplitude of the applied stress. There was the critical stress at which the microstructure change started at each test temperature higher than 500°C, and the activation energy of the change was determined as a function of temperature and the amplitude of the applied stress. The dominant factor of the microstructure change was the stress-induced acceleration of the atomic diffusion of the component elements in the alloy. In order to improve the long-term reliability of the alloy, it is very important to increase the activation energy by modifying the microstructure of this alloy.

Impression Creep Behaviour of Extruded Mg-Sn Alloy

2016 ◽  
Vol 8 (3) ◽  
Author(s):  
V. Thenambika ◽  
S. Jayalakshmi ◽  
R.A. Singh ◽  
J.K. Nidhi ◽  
M. Gupta
Keyword(s):  
Activation Energy ◽  
Stress Exponent ◽  
Creep Deformation ◽  
Creep Behaviour ◽  
Impression Creep ◽  
Temperature Dependent ◽  
Creep Tests ◽  
Automobile Engine ◽  
Creep Curves ◽  
Mg2sn Phase

Mg-Sn alloys contain thermally stable Mg2Sn phase, and are proposed as heat-resistant alloys for automobile engine applications. In this study, the creep behaviour of Mg-5Sn alloy was investigated using impression creep technique. The impression creep tests were carried out under constant punching stress in the range of 80-320 MPa at temperatures 373-573 K, for dwell times up to 5 hours. The results highlight that creep of Mg-5Sn alloy was load and temperature dependent, i.e. increasing the load and temperature resulted in larger creep deformation and hence to higher creep rates. From the creep curves, the stress exponent and the activation energy were estimated and the creep mechanism was identified.

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