Strain Hardening by High Density SISFs During Low Cycle Fatigue in Ni3(Al,Zr) Single Crystal

1994 ◽  
Vol 364 ◽  
Author(s):  
Yuefeng Gu ◽  
Yi Liu ◽  
Jianting Guo ◽  
Dongliang Lin
Keyword(s):  
Electron Microscope ◽  
Single Crystal ◽  
Strain Hardening ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Stacking Faults ◽  
Cyclic Strain ◽  
Cycle Fatigue ◽  
Transmission Electron ◽  
Stress Asymmetry

AbstractStress response and its correlation with dislocation substructures in Ni3(Al,Zr) single crystal fatigued at room temperature have been studied. Cyclic strain hardening was found to be asymmetric and increased with increasing applied cyclic strain. Transmission Electron Microscope (TEM) observation showed that there are a profusion superlattic intrinsic stacking faults (SISFs) in fatigued Ni3(Al,Zr) single crystal samples. The cyclic strain hardening and stress asymmetry are explained by the movement of the SISF.

Microstructure Evolution of a Precipitation Hardened Cu-Ni-Si Alloy during Low Cycle Fatigue

2016 ◽  
Vol 258 ◽  
pp. 546-549 ◽  
Author(s):  
Maxime Delbove ◽  
Jean Bernard Vogt ◽  
Jeremie Bouquerel ◽  
Thierry Soreau ◽  
Nicolas François ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Copper Matrix ◽  
Cycle Fatigue ◽  
Strain Variation ◽  
Deformation Bands ◽  
Strain Localisation ◽  
Transmission Electron ◽  
Mechanisms Of Plasticity

The low cycle fatigue (LCF) resistance of a precipitation hardened Cu-Ni-Si alloy has been investigated. Fully reversed strain controlled LCF tests were performed in air at room temperature at a total strain variation Δεt included between 0.6 and 1.5% and at a strain rate equal to 4.10-3 s-1. The cyclic accommodation of the alloy is composed of a hardening step (for Δεt > 0.8 %) followed by a continuous softening until the specimen fracture, except at Δεt = 0.6 % where only a slight softening is observed. For all tested strain variations, the microstructure study of the fatigued alloy by transmission electron microscope (TEM) revealed some grains with a high density of isolated short dislocations pinned between two nanoprecipitates. For Δεt ≥ 0.8 %, some grains present also deformation bands observed by TEM. The strain localisation into these bands implies an important shearing of the precipitates. It leads to their dissolution into the copper matrix and forms precipitate-free bands. The resulting macroscale cyclic accommodation depends on the ratio between the two mechanisms of plasticity accommodation at the microscale.

High-Temperature Fatigue Properties of Single Crystal Superalloys in Air and Hydrogen

2004 ◽  
Vol 126 (3) ◽  
pp. 590-603 ◽  
Author(s):  
N. K. Arakere
Keyword(s):  
Fatigue Life ◽  
Single Crystal ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Turbine Blades ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Fatigue Data ◽  
Blade Tip ◽  
Pressure Hydrogen

Hot section components in high-performance aircraft and rocket engines are increasingly being made of single crystal nickel superalloys such as PWA1480, PWA1484, CMSX-4, and Rene N-4 as these materials provide superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over their polycrystalline counterparts. Fatigue failures in PWA1480 single crystal nickel-base superalloy turbine blades used in the space shuttle main engine fuel turbopump are discussed. During testing many turbine blades experienced stage II noncrystallographic fatigue cracks with multiple origins at the core leading edge radius and extending down the airfoil span along the core surface. The longer cracks transitioned from stage II fatigue to crystallographic stage I fatigue propagation, on octahedral planes. An investigation of crack depths on the population of blades as a function of secondary crystallographic orientation (β) revealed that for β=45+/−15 deg tip cracks arrested after some growth or did not initiate at all. Finite element analysis of stress response at the blade tip, as a function of primary and secondary crystal orientation, revealed that there are preferential β orientations for which crack growth is minimized at the blade tip. To assess blade fatigue life and durability extensive testing of uniaxial single crystal specimens with different orientations has been tested over a wide temperature range in air and hydrogen. A detailed analysis of the experimentally determined low cycle fatigue properties for PWA1480 and SC 7-14-6 single crystal materials as a function of specimen crystallographic orientation is presented at high temperature (75°F–1800°F) in high-pressure hydrogen and air. Fatigue failure parameters are investigated for low cycle fatigue data of single crystal material based on the shear stress amplitudes on the 24 octahedral and 6 cube slip systems for FCC single crystals. The max shear stress amplitude [Δτmax] on the slip planes reduces the scatter in the low cycle fatigue data and is found to be a good fatigue damage parameter, especially at elevated temperatures. The parameter Δτmax did not characterize the room temperature low cycle fatigue data in high-pressure hydrogen well because of the noncrystallographic eutectic failure mechanism activated by hydrogen at room temperature. Fatigue life equations are developed for various temperature ranges and environmental conditions based on power-law curve fits of the failure parameter with low cycle fatigue test data. These curve fits can be used for assessing blade fatigue life.

Transmission electron microscope investigation of indentation induced dislocation configurations on the (001) GaSb face

1994 ◽  
Vol 209 (3) ◽  
Author(s):  
J. Doerschel
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Room Temperature ◽  
Stacking Faults ◽  
Electron Microscope Investigation ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Induced Dislocation

AbstractDislocation configurations induced by room temperature microindentations on the (001) face of GaSb (undoped and Te-doped) have been studied using high voltage transmission electron microscopy. Perfect and partial dislocations could be found in all four arms of the dislocation rosette around the indent. Microtwins and rarely single stacking faults are associated with the partials. Contrary to other binary III–V compounds, an “inverse” glide prism along the [1[unk]0]/[[unk]10] rosette arms is created and it is bounded by {111}

Effect of T6 Treatment on Low-Cycle Fatigue Properties of Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc Alloy

2014 ◽  
Vol 664 ◽  
pp. 28-33
Author(s):  
Ying Lan ◽  
Li Jia Chen ◽  
Xin Che ◽  
Feng Li
Keyword(s):  
Strain Hardening ◽  
Low Cycle Fatigue ◽  
Aging Treatment ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cyclic Strength ◽  
Fatigue Properties ◽  
Strain Hardening Exponent ◽  
Cycle Fatigue ◽  
Linear Behavior

The low-cycle fatigue behaviors of as-extruded and T6 treated Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc alloys at room temperature have been investigated under those total-strain amplitudes ranged from 0.3% to 1.0%, and the influence of T6 treatment on the low-cycle fatigue properties of Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc alloy was clarified. The experimental results show that during fatigue deformation, the significant cyclic strain hardening and stable cyclic stress response can be noted for both as-extruded and T6 treated Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc alloys. The fatigue life of as-extruded Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc alloy at all strain amplitudes is longer than that of the alloy subjected to T6 aging treatment. The relationship between both elastic and plastic strain amplitudes with reversals to failure shows a monotonic linear behavior, and can be described by the Basquin and Coffin-Manson equations, respectively. The T6 treatment can significantly increase the cyclic strain hardening exponent and cyclic strength coefficient of extruded Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc alloy.

The low-cycle fatigue deformation mechanisms of two single crystal superalloys at room temperature and 600 °C

2019 ◽  
Vol 171 ◽  
pp. 122-125 ◽  
Author(s):  
Yaoli Zhang ◽  
Xinguang Wang ◽  
Jinguo Li ◽  
Yin Cheng ◽  
Yanhong Yang ◽  
...  
Keyword(s):  
Single Crystal ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Deformation Mechanisms ◽  
Cycle Fatigue ◽  
Fatigue Deformation

Reconstruction of electron holograms recorded in a non-FEG, non-biprism TEM

1995 ◽  
Vol 53 ◽  
pp. 618-619
Author(s):  
Z.L. Wang
Keyword(s):  
Electron Microscope ◽  
Single Crystal ◽  
Experimental Technique ◽  
Transmission Electron Microscope ◽  
The Other ◽  
Electron Holography ◽  
Transmission Electron ◽  
Coherent Sources ◽  
Imaging Theory ◽  
Normal Specimen

An experimental technique for performing electron holography using a non-FEG, non-biprism transmission electron microscope (TEM) has been introduced by Ru et al. A double stacked specimens, one being a single crystal foil and the other the specimen, are loaded in the normal specimen position in TEM. The single crystal, which is placed onto the specimen, is responsible to produce two beams that are equivalent to two virtual coherent sources illuminating the specimen beneath, thus, permitting electron holography of the specimen. In this paper, the imaging theory of this technique is described. Procedures are introduced for digitally reconstructing the holograms.

Observation of dislocations in dynamically loaded Cu-SiO2

1986 ◽  
Vol 44 ◽  
pp. 424-425
Author(s):  
D. S. Pritchard
Keyword(s):  
Electron Microscope ◽  
Strain Rate ◽  
Single Crystal ◽  
Transmission Electron Microscope ◽  
Volume Fraction ◽  
Screw Dislocations ◽  
Spherical Inclusions ◽  
Transmission Electron ◽  
Crystal Dispersion ◽  
Strain Rate Loading

The effect of varying the strain rate loading conditions in compression on a copper single crystal dispersion-hardened with SiO2 particles has been examined. These particles appear as small spherical inclusions in the copper lattice and have a volume fraction of 0.6%. The structure of representative crystals was examined prior to any testing on a transmission electron microscope (TEM) to determine the nature of the dislocations initially present in the tested crystals. Only a few scattered edge and screw dislocations were viewed in those specimens.

Observations of thick and thin sections in a field-emission SEM

1994 ◽  
Vol 52 ◽  
pp. 1018-1019
Author(s):  
W. P. Wergin ◽  
S. Roy ◽  
E. F. Erbe ◽  
C. A. Murphy ◽  
C. D. Pooley
Keyword(s):  
Electron Microscope ◽  
Field Emission ◽  
Room Temperature ◽  
Osmium Tetroxide ◽  
Uranyl Acetate ◽  
Chemical Fixation ◽  
Thin Sections ◽  
Transmission Electron ◽  
Conventional Transmission Electron Microscope ◽  
Scanning Electron

Larvae of the nematode, Steinernema carpocapsae Weiser strain All, were cryofixed and freezesubstituted for 3 days in acetone containing 2% osmium tetroxide according to established procedures. Following chemical fixation, the nematodes were brought to room temperature, embedded in Spurr's medium and sectioned for observation with a Hitachi S-4100 field emission scanning electron microscope that was equipped with an Oxford CT 1500 Cryotrans System. Thin sections, about 80 nm thick, similar to those generally used in conventional transmission electron microscope (TEM) studies were mounted on copper grids and stained with uranyl acetate for 30 min and lead citrate for 5 min. Sections about 2 μm thick were also mounted and stained in a similar fashion. The grids were mounted on an Oxford grid holder, inserted into the microscope and onto a cryostage that was operated at ambient temperature. Thick and thin sections of the larvae were evaluated and photographed in the SEM at different accelerating voltages. Figs. 4 and 5 have undergone contrast conversion so that the images would resemble transmitted electron micrographs obtained with a TEM.

Electron microscope studies of the plastic deformation of ternary alloys based on GaAs

1990 ◽  
Vol 48 (4) ◽  
pp. 1120-1120
Author(s):  
R. Haswell ◽  
U. Bangert ◽  
P. Charsley
Keyword(s):  
Plastic Deformation ◽  
Electron Microscope ◽  
Room Temperature ◽  
Stacking Faults ◽  
The Other ◽  
Ternary Alloys ◽  
Dislocation Mobility ◽  
Semiconducting Materials ◽  
Micro Indentation

A knowledge of the behaviour of dislocations in semiconducting materials is essential to the understanding of devices which use them . This work is concerned with dislocations in alloys related to the semiconductor GaAs . Previous work on GaAs has shown that microtwinning occurs on one of the <110> rosette arms after indentation in preference to the other . We have shown that the effect of replacing some of the Ga atoms by Al results in microtwinning in both of the rosette arms.In the work to be reported dislocations in specimens of different compositions of Gax Al(1-x) As and Gax In(1-x) As have been studied by using micro indentation on a (001) face at room temperature . A range of electron microscope techniques have been used to investigate the type of dislocations and stacking faults/microtwins in the rosette arms , which are parallel to the [110] and [10] , as a function of composition for both alloys . Under certain conditions microtwinning occurs in both directions . This will be discussed in terms of the dislocation mobility.

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