Creep of Si3N4 Based Ceramics for Thermo-Mechanical Applications

2008 ◽  
Vol 591-593 ◽  
pp. 667-672
Author(s):  
Claudinei dos Santos ◽  
Kurt Strecker ◽  
M.J.R. Barboza ◽  
Francisco Piorino Neto ◽  
Olivério Moreira Macedo Silva ◽  
...  
Keyword(s):  
Activation Energy ◽  
Rare Earth ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Phase Content ◽  
Creep Tests ◽  
Intergranular Phase ◽  
Aspect Ratios ◽  
Compressive Stresses ◽  
N2 Atmosphere

Commercial α−Si3N4, Al2O3 and a mixed yttrium and rare earth oxides, RE2O3, were used as starting-powders. Powder batches were milled using different Al2O3/RE2O3 contents, as additive. Hot-pressing was done at 1750oC-30 min-20MPa in N2 atmosphere. Specimens neat to 6x3x3mm3 were polished and characterized by XRD and SEM. Specimens were submitted to creep tests, under compressive stresses between 100 and 350 MPa at temperatures ranging from 1250 to 1300oC in air. Higher additive amounts resulted in larger grains of higher aspect ratios and in a decreased anisotropy in the hot-pressed ceramics. The compressive creep behavior depends on the intergranular phase content. While higher amounts of additives resulted in higher creep rates, • ε , and higher stress exponents, n, the activation energy Qss, has been inferior for samples with lower additive contents. Grain sliding has been identified to be the predominant mechanism responsible for creep deformation of these ceramics.

Creep Behavior of Two Series Magnesium Alloys

2010 ◽  
Vol 638-642 ◽  
pp. 1596-1601 ◽  
Author(s):  
Yang Shan Sun ◽  
Jing Bai ◽  
Feng Xue
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Stress Exponent ◽  
Magnesium Alloys ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Grain Boundary Sliding ◽  
Creep Tests ◽  
Sharp Drop ◽  
Creep Properties

The creep behavior of two series of magnesium alloys, Mg-4Al based alloys with strontium addition and binary Mg-Nd alloys, has been studied. Results show that the high creep properties achieved by the Mg-Nd alloys are attributed to the precipitation of tiny dispersed β’ particles, which form and effectively restrict the dislocation slipping and climb during creep deformation. In terms of values of the stress exponent and apparent activation energy gained from systematic creep tests, the mechanism responsible for creep deformation of the Mg-Nd alloys is inferred as dislocation climb, which is supported by TEM observations performed on the Mg-2Nd alloy after creep test. For the Mg-4Al based alloys, however, microstructural observations reveal that the significant improvement on creep properties caused by Sr addition is accounted for the formation of an interphase network consisting of Al4Sr and a Mg-Al-Sr ternary compound distributing at grain boundaries. The breakage of the interphase network after extrusion results in a sharp drop of creep properties, indicating the creep deformation of the alloy is controlled mainly by grain boundary sliding, which is in contradiction to the mechanism for creep of the alloys inferred by the classical criterions based on the values of stress exponent and apparent activation energy.

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.

Investigation on Creep Behavior of Grade 91 Heat-Resistant Steel at 923K

2016 ◽  
Vol 853 ◽  
pp. 163-167
Author(s):  
Fa Cai Ren ◽  
Xiao Ying Tang
Keyword(s):  
Creep Rate ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Deformation Behavior ◽  
Minimum Creep Rate ◽  
Resistant Steel ◽  
Creep Tests ◽  
Heat Resistant Steel ◽  
Heat Resistant ◽  
Grade 91

Creep deformation behavior of SA387Gr91Cl2 heat-resistant steel used for steam cooler has been investigated. Creep tests were carried out using flat creep specimens machined from the normalized and tempered plate at 973K with stresses of 100, 125 and 150MPa. The minimum creep rate and rupture time dependence on applied stress was analyzed. The analysis showed that the heat-resistant steel obey Monkman-Grant and modified Monkman-Grant relationships.

scholarly journals The Creep Activation Energies of Ice

1978 ◽  
Vol 21 (85) ◽  
pp. 429-444 ◽  
Author(s):  
D. R. Homer ◽  
J. W. Glen
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Creep Deformation ◽  
Tensile Axis ◽  
Strain Rates ◽  
Boundary Slip ◽  
Creep Tests ◽  
Creep Activation Energy ◽  
Single Grain ◽  
Image Position

AbstractMonocrystals and bicrystals of ice have been creep tested at temperatures between 4 and — 30°C. The bicrystals had a single grain boundary running parallel to the tensile axis; this configuration inhibited grain-boundary slip between the two grains. The creep tests, which were carried out at constant stress σ and temperature T, yielded data of strain ϵ for time elapsed since the start of the test. These data showed accelerating creep for both monocrystals and bicrystals at all strain levels. Strain-rates were derived at strains of 0.01, 0.05. and 0.10, and these rates were fitted to the expressionk is Boltzmann’s constant and E is the creep activation energy. Derived values of n were 1.9 for monocrystals and 2.9 for bicrystals. The creep activation energy was found to be 78 kJ/mol for monocrystals and 75 kJ/mol for bicrystals. The processes of creep deformation in mono-, bi- and polycrystals are discussed.

Creep Behavior of Multi-Cation α-SiAlON Partially Stabilized Produced with an Yttrium-Rare Earth Oxide Mixture(CRE2O3)

2005 ◽  
Vol 498-499 ◽  
pp. 575-580
Author(s):  
Claudinei dos Santos ◽  
Kurt Strecker ◽  
M.J.R. Barboza ◽  
Sandro Aparecido Baldacim ◽  
Francisco Piorino Neto ◽  
...  
Keyword(s):  
Solid Solution ◽  
Rare Earth ◽  
High Temperature ◽  
Liquid Phase ◽  
Creep Behavior ◽  
Rare Earth Oxide ◽  
Si3n4 Ceramic ◽  
Creep Tests ◽  
Oxide Mixture ◽  
Metallic Cations

a−SiAlON (a’) is a solid solution of a−Si3N4, where Si and N are substituted by Al and O, respectively. The principal stabilizers of the a’-phase are Mg, Ca, Y and rare earth cations. In this way, the possible use of the yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, in obtaining these SiAlONs was investigated. Samples were sintered by hotpressing at 17500C, for 30 minutes, using a sintering pressure of 20 MPa. Creep behavior of the hot-pressed CRE-a-SiAlON/b-Si3N4 ceramic was investigated, using compressive creep tests, in air, at 1280 to 1340 0C, under stresses of 200 to 350 MPa, for 70 hours. This type of ceramic exhibited high creep and oxidation resistance. Its improved high-temperature properties are mainly due to the absence or reduced amount of intergranular phases, because of the incorporation of the metallic cations from the liquid phase formed during sintering into the Si3N4 structure, forming a a’/b composite.

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.

scholarly journals Effect of Superpave Short-Term Aging on Binder and Asphalt Mixture Rheology

2017 ◽  
Vol 45 (4) ◽  
pp. 196 ◽  
Author(s):  
Khaled Z. Ramadan ◽  
Aboqdais A. Saad
Keyword(s):  
Creep Behavior ◽  
Creep Deformation ◽  
Asphalt Binder ◽  
Testing Machine ◽  
Short Term ◽  
Creep Tests ◽  
Asphalt Mixes ◽  
Insignificant Effect ◽  
Aging Period ◽  
Asphalt Mix

This study aimed to evaluate the effect of Superpave short term aging period length and type of additive used in modifying the asphalt binder on the creep behavior of asphalt binder and asphalt mix. Hot-mix asphalt (HMA) specimens were prepared at optimum asphalt content using unmodified asphalt, or asphalt with 4% by weight of SBS or PE. The Universal Testing Machine was used to conduct dynamic creep tests. Tests results indicated that the effect of extending the aging period on creep deformation is highly dependent on type of additive used in preparing the asphalt mix. Extending the aging period more than three hours caused insignificant effect of creep behavior of control asphalt mixes. On the other hand, extending the aging period more than one hour caused insignificant effect of creep behavior of asphalt mixes prepared using SBS additive. While for mixes prepared using PE, the creep deformation continues to decrease as aging period increase.

scholarly journals Tensile Creep Behavior of Single-Crystal High-Entropy Superalloy at Intermediate Temperature

Crystals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 28
Author(s):  
Takuma Saito ◽  
Akira Ishida ◽  
Michinari Yuyama ◽  
Yuji Takata ◽  
Kyoko Kawagishi ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Single Crystal ◽  
Applied Stress ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Deformation Mechanism ◽  
Microscope Observation ◽  
Electron Microscope Observation ◽  
Creep Tests ◽  
High Entropy

In this study, we investigated the creep deformation mechanism of a single-crystal high-entropy superalloy (HESA) with the spherical γ′ precipitates at 760 °C. Before the creep tests, long-term aging tests at 760 °C without load were conducted, which showed Ostwald ripening of the secondary γ′ precipitates up to 50 h. The creep tests revealed that in the range of 500 and 600 MPa at 760 °C, the creep deformation mechanism of HESA was independent of applied stress in both the primary and secondary creep regions. The deformation mechanism of HESA was further investigated under the condition of 760 °C and 520 MPa by performing creep interrupted tests and microstructural analysis. Scanning electron microscope observation showed elongated γ′ precipitates along the applied stress axis near the ruptured surface. This could have been caused by the multi-slip around <100> preceded by the lattice rotation into <100> along the tensile axis, which was confirmed by the electron backscatter diffraction analysis. Transmission electron microscope observation of the creep interrupted and ruptured specimens showed bypass and climb motion of dislocations in the 2-h interrupted, shearing of the γ′ precipitates by the paired straight dislocations in the 50-h interrupted, and shearing of the γ′ precipitates by both the straight and the curved paired dislocations in the ruptured specimens, respectively. The secondary γ′ precipitates do not affect creep behavior as long as the deformation mechanism is a bypass and climb motion of dislocations.

scholarly journals The Creep Activation Energies of Ice

1978 ◽  
Vol 21 (85) ◽  
pp. 429-444 ◽  
Author(s):  
D. R. Homer ◽  
J. W. Glen
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Creep Deformation ◽  
Tensile Axis ◽  
Strain Rates ◽  
Boundary Slip ◽  
Creep Tests ◽  
Creep Activation Energy ◽  
Single Grain ◽  
Image Position

Abstract Monocrystals and bicrystals of ice have been creep tested at temperatures between 4 and — 30°C. The bicrystals had a single grain boundary running parallel to the tensile axis; this configuration inhibited grain-boundary slip between the two grains. The creep tests, which were carried out at constant stress σ and temperature T, yielded data of strain ϵ for time elapsed since the start of the test. These data showed accelerating creep for both monocrystals and bicrystals at all strain levels. Strain-rates were derived at strains of 0.01, 0.05. and 0.10, and these rates were fitted to the expression k is Boltzmann’s constant and E is the creep activation energy. Derived values of n were 1.9 for monocrystals and 2.9 for bicrystals. The creep activation energy was found to be 78 kJ/mol for monocrystals and 75 kJ/mol for bicrystals. The processes of creep deformation in mono-, bi- and polycrystals are discussed.

Statistical analysis of creep behavior in thermoset and thermoplastic composites reinforced with carbon and glass fibers

2020 ◽  
pp. 030932472097663
Author(s):  
Francisco Maciel Monticeli ◽  
Ana Karoline dos Reis ◽  
Roberta Motta Neves ◽  
Luis Felipe de Paula Santos ◽  
Edson Cocchieri Botelho ◽  
...  
Keyword(s):  
Creep Behavior ◽  
Glass Fibers ◽  
Laminated Composite ◽  
Analytical Models ◽  
Thermoplastic Composites ◽  
Temperature Dependent ◽  
Creep Tests ◽  
Thermoset Composites ◽  
Strain Behavior ◽  
Sensitivity Range

The thermoplastic and thermoset laminates reinforced with different fibers generate variations in the laminated composite mechanical behavior. This work aims to analyze thermoplastic and thermoset composites creep behavior with a reduced number of experiments, applying curve-fitting analytical models (Weibull and Findley) and statistical approach (ANOVA, F-test, and SRM) in order to describe creep behavior. Creep tests were carried out using a design of experiments to define parameter levels, aiming to reduce the number of the experiments, keeping reliability relevance. The temperature shows a stronger influence of creep deformation compared with the use of distinct materials. Thermoplastic matrices seem to be more sensitive to deformation, decreasing the reinforcement contribution. On the other hand, the creep resistance of the thermoset matrix conducts a significant contribution of strain behavior for the reinforcement used. The Findley model showed a temperature-dependent response. While, the Weibull-based model exhibits temperature and material-dependence, ensuring a greater sensitivity range of the parameters applied, an essential factor for a more realistic method description.

Sign in / Sign up

Export Citation Format

Share Document