scholarly journals Twinning-Induced Abnormal Strain Rate Sensitivity and Indentation Creep Behavior in Nanocrystalline Mg Alloy

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7104
Author(s):  
Shilun Yu ◽  
Yingchun Wan ◽  
Chuming Liu ◽  
Zhiyong Chen ◽  
Xiangyang Zhou
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Creep Behavior ◽  
Nanocrystalline Materials ◽  
Volume Fraction ◽  
Chemical Properties ◽  
Rate Sensitivity ◽  
Coarse Grained ◽  
Indentation Creep ◽  
Zr Alloy

Nanocrystalline materials exhibit many unique physical and chemical properties with respect to their coarse-grained counterparts due to the high volume fraction of grain boundaries. Research interests on nanocrystalline materials around the world have been lasting over the past decades. In this study, we explored the room temperature strain rate sensitivity and creep behavior of the nanocrystalline Mg–Gd–Y–Zr alloy by using a nanoindentation technique. Results showed that the hardness and creep displacements of the nanocrystalline Mg–Gd–Y–Zr alloy decreased with increasing loading strain rate. That is, the nanocrystalline Mg–Gd–Y–Zr alloy showed negative strain rate sensitivity and its creep behavior also exhibited negative rate dependence. It was revealed that the enhanced twinning activities at higher loading strain rates resulted in reduced hardness and creep displacements. The dominant creep mechanism of the nanocrystalline Mg–Gd–Y–Zr alloy is discussed based on a work-of-indentation theory in this paper.

scholarly journals Depth-Sensing Indentation Creep Behavior of Nanostructured Thermal Barrier Coatings from As-Synthesized t’-8YSZ Feedstocks

Nanomaterials ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 38
Author(s):  
Feifei Zhou ◽  
Min Liu ◽  
Yaming Wang ◽  
You Wang ◽  
Chunming Deng
Keyword(s):  
Strain Rate ◽  
Thermal Barrier Coatings ◽  
Strain Rate Sensitivity ◽  
Creep Behavior ◽  
Rate Sensitivity ◽  
Indentation Creep ◽  
Thermal Barrier ◽  
Depth Sensing ◽  
Barrier Coatings ◽  
Nano Indentation

Nano-indentation is a popular method to characterize the micromechanical properties of nanostructured 8YSZ coatings. However, little research has focused on the creep behavior of nano-indentation and only the elastic modulus and nanohardness have been analyzed. Herein, for the first time, the nano-indentation creep behavior of plasma-sprayed nanostructured 8YSZ coatings using as-prepared nanostructured non-transformable tetragonal (t’) feedstocks was investigated. The indentation creep behavior can be well characterized by the power-law equation and the strain rate sensitivity has been calculated in light of the equation. The strain rate sensitivity was sensitive to the load and the reasons were analyzed in detail. The current results can further guide and design thermal barrier coatings from the point of indentation creep property.

The strain-rate sensitivity of the hardness in indentation creep

2007 ◽  
Vol 22 (4) ◽  
pp. 926-936 ◽  
Author(s):  
A.A. Elmustafa ◽  
S. Kose ◽  
D.S. Stone
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Hertzian Contact ◽  
Indentation Creep ◽  
Proportionality Factor ◽  
Element Analysis ◽  
Elastic Deformations ◽  
The Relationship

Finite element analysis is used to simulate indentation creep experiments with a cone-shaped indenter. The purpose of the work is to help identify the relationship between the strain-rate sensitivity of the hardness, νH, and that of the flow stress, νσ in materials for which elastic deformations are significant. In general, νH differs from νσ, but the ratio νH/νσ is found to be a unique function of H/E* where H is the hardness and E* is the modulus relevant to Hertzian contact. νH/νσ approaches 1 for small H/E*, 0 for large H/E*, and is insensitive to work hardening. The trend in νH/νσ as a function of H/E* can be explained based on a generalized analysis of Tabor’s relation in which hardness is proportional to the flow stress H = k × σeff and in which the proportionality factor k is a function of σeff/E*.

The Effect of Controlled Melt-Solidification on the Strain Rate Sensitivity of a Squeeze-Cast Hybrid-Reinforced Aluminum AA 6061 Matrix Composite

2015 ◽  
Vol 16 ◽  
pp. 1-16
Author(s):  
B.O. Malomo ◽  
O.O. Fadodun ◽  
K.M. Oluwasegun ◽  
A.T. Ogunbodede ◽  
S.A. Ibitoye ◽  
...  
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Matrix Composite ◽  
Deformation Behavior ◽  
Squeeze Casting ◽  
Volume Fraction ◽  
Tensile Elongation ◽  
Testing Machine ◽  
Rate Sensitivity ◽  
Cooling Rates

A framework based on the relationship between variations in cooling rates and volume fraction of reinforcements during solidification processing to enhance the deformation behavior of aluminum alloy AA6061 matrix composite produced with a hybrid system of reinforcements is investigated in this study. The aluminum matrix composite with 5 %, 10 % and 20 % volume fraction of reinforcements (Al2O3-SiC) was synthesized by infiltrating molten aluminum AA 6061 at a pouring temperature of 740 °C into prefabricated preforms of reinforcements at a pressure of 80 MPa, die preheat temperature of 300 °C and pressure holding time of 15 s using the squeeze casting method. By employing water jet spraying at the rate of 0.1, 0.2 and 0.3 kg/s and taking measurements using a K-type thermocouple, cooling rates were obtained in correspondence with varying volume fractions of reinforcements. The developed composites were sectioned and microstructural features were examined by optical microscopy. Tensile testing was conducted according to ASTM B557 standard using an MTS testing machine. It was observed that cooling rates decreased as the volume fraction of reinforcements was increased and the cooling time also increased accordingly during this process. With respect to deformation behavior, higher cooling rates are associated with an improvement in mechanical properties at 5 % and 10 % additions of hybrid reinforcement particles but this effect diminishes as the volume fraction of reinforcements was increased to 20 %. Also, the strain rate sensitivity (SRS) exponent increased considerably with strain rates and volume fraction of reinforcements, but the tensile elongation values decreased with increasing volume fraction of reinforcements; and the variations in these properties were most significant for samples containing 20% volume fraction of hybrid reinforcements.From the foregoing, it follows that an experimentally-determined optimal solidification range is critical to the enhancement of deformation parameters as the volume fraction of reinforcements is varied in a squeeze casting process.

Strain Rate Sensitivity of 31Mn-3Al-3Si TWIP Steel with Partially Recrystallized Fine Grained Structure

2008 ◽  
Vol 584-586 ◽  
pp. 673-678 ◽  
Author(s):  
Rintaro Ueji ◽  
Kenji Harada ◽  
Akihiko Takemura ◽  
Kazutoshi Kunishige
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Twip Steel ◽  
Volume Fraction ◽  
Tensile Deformation ◽  
Cell Structure ◽  
Rate Sensitivity ◽  
Dislocation Cell ◽  
Annealed Specimen ◽  
Deformation Behaviors

Strain rate sensitivity of the strength of TWIP (Twinning Induced Plasticity) steel with the mixture of recrystallized fine grains and rolling-deformation microstructures was studied. The 31mass%Mn-3%Al-3%Si TWIP steel sheet was severely cold-rolled to a reduction of 92% and subsequently annealed at various temperatures ranging from 600oC to 700oC in order to obtain the partial recrystallized microstructure with various fraction of recrystallized microstructure. The 600oC annealed specimen keeps similar morphologies as observed in the as-rolled structure consisting of both the fine lamellar dislocation cell structure and the twin/matrix lamellar structure; whereas, in the specimen annealed at 625oC or 675oC , the partially recrystallized fine grains (d~1µm) with a few dislocations evolve. The volume fraction of recrystallized fine grains increases with increasing of the annealing temperature while the mean diameter of the recrystallized grains is not changed largely. The tensile deformation behaviors were measured at various strain rates ranging from 10-3sec-1 to 102sec-1. The strength and elongation become smaller and larger, respectively, with increasing the fraction of the recrystallized microstructure. The activation volume of dislocations becomes larger with increasing the fraction of recrystallized microstructure.

Grain Refinement during Superplastic Deformation of Coarse-Grained Al-Mg-Cu Alloys

2006 ◽  
Vol 509 ◽  
pp. 75-80 ◽  
Author(s):  
M.I. Cruz-Palacios ◽  
D. Hernández-Silva ◽  
L.A. Barrales-Mora ◽  
M.A. García-Bernal
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Grain Refinement ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Mg Alloy ◽  
Coarse Grained ◽  
Dislocation Creep ◽  
Rolled Plate ◽  
Strain Rates

In the present study the superplastic behavior of Al-6%Mg–0.5%Cu and Al–8%Mg– 0.5%Cu in a coarse grain size condition has been studied. The alloys are melted in an electrical furnace under argon atmosphere. The ingots (25 mm thick) are homogenized at 400 °C during 72 h and then rolled at 430 °C to a thickness of 5 mm. The mean grain size after rolling is 55 µm for the 6%Mg alloy and 61 µm for the 8%Mg alloy. Tensile test specimens are machined from the rolled plate in the rolling direction. Strain-rate-change tests at temperatures between 300 and 450 °C and strain rates between 1x10-4 and 1x10-1 s-1 are carried out to determine the strain rate sensitivity of the flow stress. Finally, elongation to failure tests are conducted at temperatures and strain rates where the alloys show a high strain rate sensitivity. Elongations higher than 390 % are obtained for the 8%Mg alloy. It is observed that the grip regions of the deformed samples show coarser grains than the regions near to the fracture surface. This means that grain refinement takes place during deformation, suggesting that the principal deformation mechanism is dislocation creep.

Strain rate sensitivity and deformation activation volume of coarse-grained and ultrafine-grained TiNi alloys

2015 ◽  
Vol 102 ◽  
pp. 99-102 ◽  
Author(s):  
D.V. Gunderov ◽  
G. Maksutova ◽  
A. Churakova ◽  
A. Lukyanov ◽  
A. Kreitcberg ◽  
...  
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Activation Volume ◽  
Rate Sensitivity ◽  
Coarse Grained ◽  
Ultrafine Grained

Enhanced Formability in Sheet Metals Produced by Cladding a High Strain-Rate Sensitive Layer

2013 ◽  
Vol 81 (2) ◽  
Author(s):  
X. H. Hu ◽  
P. D. Wu ◽  
D. J. Lloyd ◽  
J. D. Embury
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Volume Fraction ◽  
Rate Sensitivity ◽  
Core Material ◽  
Sensitive Layer ◽  
Element Analysis ◽  
Clad Sheet ◽  
Clad Layer ◽  
The One

The necking behavior of cladding sheets with a rate-sensitive layer cladding on a rate-insensitive core material has been studied. A nonlinear long-wavelength analysis, similar to the one proposed by Hutchinson and Neale (1977, “Influence of Strain-Rate Sensitivity on Necking Under Uniaxial Tension,” Acta Metal., 25, pp. 839–846) for monolithic rate-sensitive materials, is developed to identify the onset of necking in a rate-sensitive clad sheet. This relatively simple analysis is validated by comparing its numerical results with those based on more complicated finite element analysis. It is demonstrated that for monolithic rate-sensitive materials the proposed nonlinear analysis reduces to the one developed by Hutchinson and Neale (1977). For cladding sheets, it is found that the necking strain increases monotonically by increasing the strain-rate sensitivity of the clad layer if the volume fraction of cladding is fixed. It is also revealed that, for fixed strain-rate sensitivity of the clad layer, necking localization is retarded by increasing the volume fraction of the cladding layer.

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