Effective Stresses and Plastic Strain Rates in a Superalloy: a High Temperature In Situ Study by Synchrotron X-Ray TCD

2006 ◽  
Vol 524-525 ◽  
pp. 775-780 ◽  
Author(s):  
Alain Jacques ◽  
Olivier Ferry ◽  
Frédéric Diologent ◽  
Pierre Caron ◽  
Pierre Bastie
Keyword(s):  
High Temperature ◽  
Plastic Strain ◽  
Tensile Axis ◽  
Young Modulus ◽  
High Energy ◽  
Strain Rates ◽  
Data Scatter ◽  
Von Mises ◽  
Von Mises Stresses

Variations in the lattice parameters of γ and γ' phases perpendicular to the [001] tensile axis were recorded in situ at ~10 minutes intervals using the Triple Axis Diffractometer of the High Energy (ID15) beamline at ESRF. Testing was carried out on an AM1 superalloy specimen with a raft microstructure at high temperature (1072°C) under load steps between 0 MPa and 300 MPa. These data were used to evaluate the Young modulus and the effective (Von Mises) stresses within the γ' rafts and γ corridors, as well the average plastic strain rates of each phase. The recorded stress data scatter was within the MPa range, and should be good enough to probe the elementary mechanisms of plasticity.

scholarly journals Dislocation Densities and Velocities within the γ Channels of an SX Superalloy during In Situ High-Temperature Creep Tests

Materials ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 1527 ◽  
Author(s):  
Thomas Schenk ◽  
Roxane Trehorel ◽  
Laura Dirand ◽  
Alain Jacques
Keyword(s):  
High Temperature ◽  
Plastic Strain ◽  
Applied Stress ◽  
Load Transfer ◽  
Von Mises Stress ◽  
High Temperature Creep ◽  
Creep Tests ◽  
Temperature Creep ◽  
Von Mises

The high-temperature creep behavior of a rafted [001] oriented AM1 Ni-based single crystal superalloy was investigated during in situ creep tests on synchrotrons. Experiments were performed at constant temperatures under variable applied stress in order to study the response (plastic strain, load transfer) to stress jumps. Using two different diffraction techniques in transmission (Laue) geometry, it was possible to measure the average lattice parameters of both the γ matrix and the γ ′ rafts in the [100] direction at intervals shorter than 300 s. The absolute precision with both diffraction techniques of the constrained transverse mismatch (in the rafts’ plane) is about 10−5. After stress jumps, special attention is given to the evolution of plastic strain within the γ channels. The relaxation of the Von Mises stress at leveled applied stress shows evidence of dislocation multiplication within the γ channels. From the analysis, we showed an interaction between plastic stress and dislocation density of the γ phase.

scholarly journals In Situ Measurement of Internal Stresses and Strain Rates by High Energy X-Ray Diffraction during High Temperature Mechanical Testing

2011 ◽  
Vol 278 ◽  
pp. 48-53 ◽  
Author(s):  
Alain Jacques ◽  
Laura Dirand ◽  
Jean Philippe Chateau ◽  
Thomas Schenk ◽  
Olivier Ferry ◽  
...  
Keyword(s):  
High Temperature ◽  
Mechanical Behaviour ◽  
Lattice Mismatch ◽  
High Energy ◽  
Internal Stresses ◽  
Strain Rates ◽  
X Ray Diffraction ◽  
Experimental Conditions ◽  
X Ray

The combination of high temperature (1050°C -1150°C) testing and in situ high energy X-Ray diffraction measurements using synchrotron Three Crystal Diffractometry may give various insights into the mechanical behaviour of superalloys: measurement of the lattice mismatch, order within the ' phase, elastic constants, and dynamic response to changes in the experimental conditions. Several examples are given on the rafted AM1 superalloy, resulting from experiments at the ID15A (ESRF) and BW5 (DESY) high energy beamlines.

In situsynchrotron powder diffraction study of active belite clinkers

2007 ◽  
Vol 40 (6) ◽  
pp. 999-1007 ◽  
Author(s):  
Ángeles G. De la Torre ◽  
Khadija Morsli ◽  
Mohammed Zahir ◽  
Miguel A.G. Aranda
Keyword(s):  
High Temperature ◽  
High Resolution ◽  
Powder Diffraction ◽  
Polymorphic Transformation ◽  
High Energy ◽  
Dicalcium Silicate ◽  
Polymorphic Transformations ◽  
X Ray ◽  
High Temperature Reactions

The clinkerization processes to form belite clinkers, with theoretical compositions close to 60 wt% of Ca2SiO4, have been studiedin situby high-resolution high-energy (λ = 0.30 Å) synchrotron X-ray powder diffraction. In order to obtain active belite cements, different amounts of K2O, Na2O and SO3have been added. The existence range of the high-temperature phases has been established and, furthermore, Rietveld quantitative phase analyses at high temperature have been performed for all patterns. The following high-temperature reactions have been investigated: (i) polymorphic transformations of dicalcium silicate, \alpha_{\rm L}'-Ca2SiO4↔ \alpha_{\rm H}'-Ca2SiO4from 1170 to 1230 K, and \alpha_{\rm H}'-Ca2SiO4↔ α-Ca2SiO4from 1500 to 1600 K; (ii) melting of the aluminates phases, Ca3Al2O6and Ca4(Al2Fe2)O10, above ∼1570 K; and (iii) reaction of Ca2SiO4with CaO to yield Ca3SiO5above ∼1550 K. Moreover, in all the studied compositions the temperature of the polymorphic transformation \alpha_{\rm H}'-Ca2SiO4↔ α-Ca2SiO4has decreased with the addition of activators. Finally, active belite clinkers were produced as the final samples contained α-belite phases.

scholarly journals Formation of Dislocations and Stacking Faults in Embedded Individual Grains during In Situ Tensile Loading of an Austenitic Stainless Steel

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 5919
Author(s):  
Benjamin Neding ◽  
Darren C. Pagan ◽  
Johan Hektor ◽  
Peter Hedström
Keyword(s):  
Deformation Mechanism ◽  
Grain Orientation ◽  
Profile Analysis ◽  
Tensile Axis ◽  
Stacking Faults ◽  
Tensile Loading ◽  
High Energy ◽  
Line Profile Analysis ◽  
Individual Grains

The formation of stacking faults and dislocations in individual austenite (fcc) grains embedded in a polycrystalline bulk Fe-18Cr-10.5Ni (wt.%) steel was investigated by non-destructive high-energy diffraction microscopy (HEDM) and line profile analysis. The broadening and position of intensity, diffracted from individual grains, were followed during in situ tensile loading up to 0.09 strain. Furthermore, the predominant deformation mechanism of the individual grains as a function of grain orientation was investigated, and the formation of stacking faults was quantified. Grains oriented with [100] along the tensile axis form dislocations at low strains, whilst at higher strains, the formation of stacking faults becomes the dominant deformation mechanism. In contrast, grains oriented with [111] along the tensile axis deform mainly through the formation and slip of dislocations at all strain states. However, the present study also reveals that grain orientation is not sufficient to predict the deformation characteristics of single grains in polycrystalline bulk materials. This is witnessed specifically within one grain oriented with [111] along the tensile axis that deforms through the generation of stacking faults. The reason for this behavior is due to other grain-specific parameters, such as size and local neighborhood.

Investigation of Plastic Instability in TWIP Steels by In Situ Diffraction of High Energy X-Rays

2014 ◽  
Vol 783-786 ◽  
pp. 1105-1110
Author(s):  
Jean Philippe Chateau-Cornu ◽  
Alain Jacques ◽  
Jean Philippe Tinnes ◽  
Thomas Schenk
Keyword(s):  
Plastic Strain ◽  
Elastic Anisotropy ◽  
Tensile Tests ◽  
Plastic Instability ◽  
High Energy ◽  
Nucleation Site ◽  
X Rays ◽  
Cubic Crystal ◽  
Twip Steels

We investigate the non uniform plastic deformation of a TWIP FeMnC steel by diffraction of high energy synchrotron X-rays. In particular, we observe the propagation of bands of plastic strain localisation. Debye-Scherrer rings are recorded in situ during tensile tests at two different strain rates. Discontinuous initial rings characteristic of unstrained polycristals with no texture become rapidly continuous after several percents of plastic strain due to strain gradients within the grains and a strong texture develops. The crystallographic dependence of the Young’s modulus is estimated and is consistent with the elastic anisotropy of a cubic crystal. A delay between the serrations on the macroscopic tensile curve and the stepwise variations of the diffracted peak’s position and width are consistent with propagating bands nucleating outside the X-ray beam. Slower and thinner bands are observed at the lowest strain rate. A tensile test interrupted to perform a few minute relaxation leads to a displacement of the nucleation site of the bands from one end to the middle of the gauge part.

scholarly journals Ultrahigh Strength and Shear-Assisted Decohesion of Sliding Silver Nanocontacts Studied in situ

2021 ◽  
Author(s):  
Takaaki Sato ◽  
Zachary Milne ◽  
Masahiro Nomura ◽  
Naruo Sasaki ◽  
Robert Carpick ◽  
...  
Keyword(s):  
High Strength ◽  
Contact Forces ◽  
Ideal Strength ◽  
Transmission Electron ◽  
Contact Width ◽  
Theoretical Predictions ◽  
Von Mises ◽  
Von Mises Stresses ◽  
Applied Stresses

Abstract The behavior of materials in sliding contact is challenging to determine since the interface is normally hidden from view. Using a custom microfabricated device, we conducted in situ, ultrahigh vacuum transmission electron microscope measurements of crystalline silver nanocontacts under combined tension and shear, permitting simultaneous observation of contact forces and contact width. While classically, silver exhibits substantial sliding-induced plastic junction growth, the nanocontacts exhibit only limited plastic deformation despite high applied stresses. This difference arises from the nanocontacts’ high strength, as we find the von Mises stresses at yield points approach the ideal strength of silver. We attributed this to the nanocontacts’ nearly defect-free nature and small size. The contacts also separate unstably, with pull-off forces well below classical predictions for rupture under pure tension. This provides in situ confirmation that shearing reduces nanoscale pull-off forces, consistent with recent theoretical predictions but never before directly observed.

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