Elevated temperature mechanical behavior of CoSi and particulate reinforced CoSi produced by spray atomization and co-deposition

1994 ◽  
Vol 9 (2) ◽  
pp. 362-371 ◽  
Author(s):  
Don Baskin ◽  
Jeff Wolfenstine ◽  
Enrique J. Lavernia
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Elevated Temperature ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Diffusional Creep ◽  
Spray Atomization ◽  
Dislocation Glide ◽  
Unreinforced Material ◽  
Particulate Reinforced

Monolithic CoSi and TiB2 reinforced CoSi materials were produced by spray atomization and co-deposition. The creep behavior of both materials at elevated temperature was investigated. The unreinforced material of grain size ≍25 μm exhibited a stress exponent of three, activation energy for creep of 320 kJ/mole, dislocation substructure of homogeneously distributed dislocations, and inverse creep transients upon stress increases. These results suggest that the creep behavior of CoSi is controlled by a dislocation glide mechanism. In contrast, the reinforced material of a finer grain size (≍10 μm) exhibited a stress exponent of unity, activation energy for creep of 240 kJ/mole, and negligible creep transients upon stress increases, suggesting that the creep behavior of the reinforced material is controlled by a diffusional creep mechanism. The creep resistance of the reinforced material was lower than that for the unreinforced material. This is a result of the finer grain size and higher porosity in the reinforced material.

Elevated temperature deformation of fine-grained La0.9Sr0.1MnO3

1996 ◽  
Vol 11 (3) ◽  
pp. 657-662 ◽  
Author(s):  
J. Wolfenstine ◽  
T. R. Armstrong ◽  
W. J. Weber ◽  
M. A. Boling-Risser ◽  
K. C. Goretta ◽  
...  
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Elevated Temperature ◽  
Perovskite Oxides ◽  
Lattice Diffusion ◽  
Diffusional Creep ◽  
Temperature Deformation ◽  
Creep Data ◽  
Fine Grained ◽  
Fine Grain

Compressive creep behavior of fine-grained (5 μm) La0.9Sr0.1MnO3with a relative theoretical density between 85 and 90% was investigated over the temperature range 1150–1300 °C in air. The fine grain size, brief creep transients, stress exponent close to unity, and absence of deformation-induced dislocations, suggested that the deformation was controlled by a diffusional creep mechanism. The activation energy for creep of La0.9Sr0.1MnO3was 490 kJ/mole. A comparison of the activation energy for creep of La0.9Sr0.1MnO3with existing diffusion and creep data for perovskite oxides suggested that the diffusional creep of La0.9Sr0.1MnO3was controlled by lattice diffusion of the cations, either lanthanum or manganese.

Creep Behavior of MoSi2 with Si3N4 Reinforcements

1996 ◽  
Vol 460 ◽  
Author(s):  
C. R. Feng ◽  
K. Sadananda
Keyword(s):  
Activation Energy ◽  
Elevated Temperature ◽  
Melting Point ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Volume Fraction ◽  
High Melting ◽  
Stress Range ◽  
High Melting Point ◽  
Compression Creep

ABSTRACTBecause of its high melting point, excellent oxidation resistance and ductility at high temperatures, MoSi2 and its composites are attractive for elevated temperature applications. In this study, the compression creep behavior of hot pressed MoSi2 with various volume fraction of Si3N4 at 1200°C, 1300°C and 1400°C were investigated. Within the stress range of 115–425MPa, the stress exponent, n, was either 1 or 5 depended on the volume fraction of Si3N4. The activation energy of creep for MoSi2-50%Si3N4 composite was 750kJ/mol. At still higher volume fraction of Si3N4, the activation energy decreases to 693kJ/mol, which is the same as that for monolithic Si3N4.

Microstructures and Creep of AM50-Sb-Gd Alloys

2005 ◽  
Vol 488-489 ◽  
pp. 749-752 ◽  
Author(s):  
Su Gui Tian ◽  
Keun Yong Sohn ◽  
Hyun Gap Cho ◽  
Kyung Hyun Kim
Keyword(s):  
Activation Energy ◽  
Creep Rate ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Deformation Mechanism ◽  
Creep Resistance ◽  
Fine Particles ◽  
Dislocation Climb ◽  
The Matrix

Creep behavior of AM50-0.4% Sb-0.9%Gd alloy has been studied at temperatures ranging from 150 to 200°C and at stresses ranging from 40 to 90 MPa. Results show that the creep rate of AM50-0.4%Sb-0.9%Gd alloy was mainly controlled by dislocation climb at low stresses under 50 MPa. The activation energy for the creep was 131.2 ± 10 kJ/mol and the stress exponent was in the range from 4 to 9 depending on the applied stress. More than one deformation-mechanism were involved during the creep of this alloy. Microstructures of the alloy consist of a–Mg matrix and fine particles, distinguished as Mg17Al12, Sb2Mg3, and Mg2Gd or Al7GdMn5 that were homogeneously distributed in the matrix of the alloy, which effectively reduced the movement of dislocations, enhancing the creep resistance. Many dislocations were identified to be present on non-basal planes after creep deformation.

Grain Size Effect on the Creep Behavior of Monolithic MoSi2

1994 ◽  
Vol 364 ◽  
Author(s):  
C.R. Feng ◽  
K. Sadananda
Keyword(s):  
Grain Size ◽  
Size Effect ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Molybdenum Disilicide ◽  
Grain Size Effect ◽  
Stress Range ◽  
Creep Stress ◽  
Creep Stress Exponent

AbstractThe grain size effect on the creep behavior of hot-pressed monolithic molybdenum disilicide was investigated at 1200°C in a 19–255 MPa stress range. The creep-stress exponent, n, increased from 1 at low stresses to 4 at high stresses. The grain size exponent, p, varied from 0, to 3.5 and to 8 depending on the grain size, the creep-stress exponent, and creep history.

Interface Controlled Diffusional Creep of Cu + 2.8 at.% Co Solid Solution

2012 ◽  
Vol 322 ◽  
pp. 33-39 ◽  
Author(s):  
Sergei Zhevnenko ◽  
Eugene Gershman
Keyword(s):  
Activation Energy ◽  
Solid Solution ◽  
Surface Tension ◽  
High Temperature ◽  
Creep Behavior ◽  
Pure Copper ◽  
Diffusional Creep ◽  
High Temperature Creep ◽  
Temperature Range ◽  
Different Temperatures

High-temperature creep experiments were performed on a Cu-2.8 ат.% Co solid solution. Cylindrical foils of 18 micrometers thickness were used for this purpose. Creep tests were performed in a hydrogen atmosphere in the temperature range of about from 1233 K to 1343 K and at stresses lower than 0.25 MPa. For comparison, a foil of pure copper and Cu-20 at.% Ni solid solution were investigated on high temperature creep. Measurements on the Cu foil showed classical diffusional creep behavior. The activation energy of creep was defined and turned out to be equal 203 kJ/mol, which is close to the activation energy of bulk self-diffusion of copper. There was a significant increase in activation energy for the Cu-20 at.% Ni solid solution. Its activation energy was about 273 kJ/mol. The creep behavior of Cu-Co solid solution was more complicated. There were two stages of diffusional creep at different temperatures. The extremely large activation energy (about 480 kJ/mol) was determined at relatively low temperature and a small activation energy (about 105 kJ/mol) was found at high temperatures. The creep rate of Cu-Co solid solution was lower than that of pure copper at all temperatures. In addition, the free surface tension of Cu-2.8 ат.% Co was measured at different temperatures from 1242 K to 1352 K. The surface tension increases in this temperature range from 1.6 N/m to 1.75 N/m. There were no features on the temperature dependence of the surface tension.

scholarly journals Microstructure and impression creep characteristics Al-9Si-xCu aluminum alloys

10.30544/101 ◽  
2015 ◽  
Vol 21 (2) ◽  
pp. 115-126 ◽  
Author(s):  
Mohsen Yousefi ◽  
Mehdi Dehnavi ◽  
S.M. Miresmaeili
Keyword(s):  
Activation Energy ◽  
Aluminum Alloys ◽  
Intermetallic Compound ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Eutectic Phase ◽  
Dislocation Creep ◽  
Impression Creep ◽  
Pipe Diffusion ◽  
Creep Characteristics

The effects of 1.5, 2.5 and 3.5 wt.% Cu additions on the microstructure and creep behavior of the as-cast Al-9Si alloy were investigated by impression tests. The tests were performed at temperature ranging from 493 to 553 K and under punching stresses in the range 300 to 414 MPa for dwell times up to 3000 seconds. The results showed that, for all loads and temperatures, the Al–9Si–3.5Cu alloy had the lowest creep rates and thus, the highest creep resistance among all materials tested. This is attributed to the formation of hard intermetallic compound of Al2Cu, and higher amount of α-Al2Cu eutectic phase. The stress exponent and activation energy are in the ranges of 5.2- 7.2 and 115 -150 kJ/ mol, respectively for all alloys. According to the stress exponent and creep activation energies, the lattice and pipe diffusion- climb controlled dislocation creep were the dominant creep mechanism.

Comparison of the High-Temperature Deformation of Alumina-Zirconia and Alumina-Zirconia-Mullite Composites

2005 ◽  
Vol 20 (1) ◽  
pp. 13-17 ◽  
Author(s):  
Tiandan Chen ◽  
Martha L. Mecartney
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
Strain Rate ◽  
Stress Exponent ◽  
Creep Behavior ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Reactive Processing ◽  
Lower Activation ◽  
Lower Activation Energy

An alumina-based ceramic codispersed with 15 vol% zirconia and 15 vol% mullite (AZM) was synthesized by reactive processing, and the creep behavior was compared to alumina with 30 vol% zirconia (AZ). Constant stress compressive creep behavior for AZM exhibited a stress exponent of 2 and an activation energy of 770 KJ/mol, while a similar stress exponent but lower activation energy of 660 KJ/mol was found for AZ. The strain rate of AZM, however, was more than twice that of the AZ under the same deformation conditions, indicating a better potential for superplastic shape forming.

Plastic deformation in icosahedral Al–Pd–Mn alloys

1994 ◽  
Vol 9 (2) ◽  
pp. 343-347 ◽  
Author(s):  
J.E. Shield ◽  
M.J. Kramer ◽  
R.W. McCallum
Keyword(s):  
Electron Microscopy ◽  
Activation Energy ◽  
Transmission Electron Microscopy ◽  
Stress Exponent ◽  
Microstructural Analysis ◽  
High Temperature Creep ◽  
Deformation Characteristics ◽  
Cast Sample ◽  
Dislocation Glide ◽  
Transmission Electron

The deformation characteristics of icosahedral Al70Pd21.5Mn8.5 have been investigated by high temperature creep experiments, and the resultant microstructures have been examined by transmission electron microscopy (TEM). From 730 to 780 °C, microstructural analysis revealed that the deformation is controlled by dislocation glide, with an activation energy of 210 ± 30 kJ/mole and a stress exponent of 1.2 ± 0.2. From 780 to 810 °C, microstructures were characteristic of deformation controlled by dislocation glide and climb. The activation energy and stress exponent were determined to be 1700 ± 80 kJ/mole and 2.9 ± 0.3, respectively. Hardness measurements also reflected an increase in dislocation density, as the hardness of the deformed samples was approximately 10% higher than the as-cast sample.

Creep behavior of a polycrystalline nickel aluminide: Ni-23.5 at.% A1-0.5 at.% Hf-0.2 at.% B

1986 ◽  
Vol 1 (1) ◽  
pp. 68-72 ◽  
Author(s):  
J. H. Schneibel ◽  
G. F. Petersen ◽  
C. T. Liu
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Creep Behavior ◽  
Nickel Aluminide ◽  
Size Dependence ◽  
Diffusional Creep ◽  
Diffusion Control ◽  
Polycrystalline Nickel ◽  
Experimental Conditions ◽  
Coble Creep

The creep behavior of a poly crystalline nickel aluminide with the composition Ni-23.5 at.% Al-0.5 at. % Hf-0.2 at. % B has been measured as a function of stress, temperature, and grain size. At high stresses, of the order of 100 MPa, the strain rate is nonlinear in the stress, with a stress exponent greater than two. Below approximately 10 MPa, at 1033 K, the steady-state strain rate is almost proportional to the stress, indicating that diffusional creep is rate controlling. Calculations of expected Nabarro—Herring and Coble creep rates did not answer whether diffusive mass transport through the grains, or along the grain boundaries, is rate controlling. The grain-size dependence of the strain rate, however, indicates predominance of volume diffusion control, i.e., Nabarro—Herring creep, for our experimental conditions.

Creep behavior of a cryomilled ultrafine-grained Al–4% Mg alloy

2000 ◽  
Vol 15 (10) ◽  
pp. 2215-2222 ◽  
Author(s):  
R. W. Hayes ◽  
V. Tellkamp ◽  
E. J. Lavernia
Keyword(s):  
Activation Energy ◽  
Thermal Stability ◽  
Grain Size ◽  
Grain Boundary ◽  
Creep Behavior ◽  
Boundary Region ◽  
Mg Alloy ◽  
Pinning Force ◽  
Ultrafine Grained ◽  
Boundary Deformation

The creep behavior of a cryomilled ultrafine-grained Al–Mg alloy was examined. The grain size ranged from 300 to 400 nm. The stress exponents ranged from 7.2 to 7.4. The apparent activation energy for creep, 83.7 kJ/mol at 27.5 MPa and 77 kJ/mol at 38 MPa, agreed well with the activation energy for grain boundary diffusion in aluminum. Transmission electron microscope analysis following creep at 300 °C to approximately 0.2% strain in 1411 h revealed the grain size was unchanged from its as-extruded size indicating significant thermal stability of this material at relatively high fractions of the melting temperature. The creep resistance of the Al–Mg alloy was rationalized in terms of an attractive interaction between grain boundary dislocations and incoherent particles within the boundary region, which suppressed grain boundary deformation. The grain boundary particles also led to high thermal stability by exerting a Zener pinning force on the grain boundaries, thus inhibiting grain growth at high temperatures.

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