TEM Observations of Dislocation Emission at Grain Boundaries in Response to Uniaxial (Tensile) Straining

1981 ◽  
Vol 39 ◽  
pp. 296-297
Author(s):  
L.E. Murr
Keyword(s):  
Grain Boundaries ◽  
Tensile Deformation ◽  
Tensile Tests ◽  
Convincing Evidence ◽  
304 Stainless Steel ◽  
Uniaxial Tensile ◽  
Dislocation Emission ◽  
Quantitative Studies ◽  
Transmission Electron

Although it now seems to be generally recognized that grain boundaries and other interfaces are sources for dislocations, there are only scant few observations which tend to show convincing evidence for this. Murr earlier suggested that dislocation pile-ups in deformed metals and alloys (especially of low stacking-fault free energy) were primarily dislocation emission profiles, and more recent quantitative studies tend to unambiguously confirm this for uniaxial tensile deformation. Some of these features are illustrated in Fig. 1(a) and (b) which show a systematic increase in the number of dislocation profiles associated with grain boundary ledges at increasing tensile strains; observed in a Hitachi H.U. 200 F transmission electron microscope.The results shown in Fig. 1(a) and (b) were obtained as part of a systematic study of dislocation emission following the straining of 304 stainless steel sheet samples in separate, conventional tensile tests. Consequently these observations, while qualitatively and even quantitatively convincing, lack the force of direct, in-situ observations.

Blends containing core-shell impact modifiers Part 1. Structure and tensile deformation mechanisms (IUPAC Technical Report)

2001 ◽  
Vol 73 (6) ◽  
pp. 897-912 ◽  
Author(s):  
C. B. Bucknall
Keyword(s):  
Tensile Deformation ◽  
Tensile Tests ◽  
Mechanical Tests ◽  
Glass Transitions ◽  
Volume Increase ◽  
Transmission Electron ◽  
Technical Report ◽  
The Matrix ◽  
20 Nm

Two impact modifiers, based respectively on polybutadiene (PB) and poly(butyl acrylate-co-styrene) (PBA), are compared in blends with four glassy polymers: polycarbonate (PC), poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (PSAN), and poly(vinyl chloride) (PVC). Dynamic mechanical tests show glass transitions at about -80 °C in PB and -15 °C in PBA. Both modifiers have grafted PMMA shells, which are seen in the transmission electron microscope (TEM) to be about 10 nm thick. The two-stage PB particles have 200-nm-diameter polybutadiene cores, whereas the three-stage PBA particles have 260-nm-diameter PMMA cores, with 20-nm thick PBA rubber inner shells. Under tension, the PB particles cavitate to form single voids on reaching a critical volume strain, and subsequently offer little resistance to dilatation. By contrast, tensile tests performed in situ in the TEM show that the PBA shells form fibrils that are anchored to the rigid core, and act as constraints on further dilatation: the stresses developed in the PBA fibrils can be sufficient to draw fibrils from both the PMMA core and the PSAN matrix. There is evidence that the PMMA shells can debond from the matrix both in cryogenic fracture and in fatigue at 23 °C. Tensile dilatometry shows that the PB particles cavitate at higher strains than the PBA particles, but that the PB particles then cause a rapid volume increase, leading to a low strain at break. By contrast, the PBA particles produce a more controlled dilatation, and higher strains to break. Later papers in this series treat the mechanical and rheological behavior of these blends in more detail.

In Situ TEM Observations of Deformation Processes in Nanocrystalline Pd

2008 ◽  
Vol 584-586 ◽  
pp. 464-469 ◽  
Author(s):  
Harald Rösner ◽  
Gerhard Wilde
Keyword(s):  
Electron Microscope ◽  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Tensile Tests ◽  
Transmission Electron ◽  
Metal Sheets ◽  
High Resolution Tem ◽  
First Results ◽  
Deformation Processes

In this study we show that in-situ tensile tests performed in a transmission electron microscope (TEM) in combination with high-resolution TEM are feasible, and, that this method is appropriate to elucidate the deformation processes in nanocrystalline materials directly. First results on nanocrystalline Pd produced by repeated cold-rolling with intermediate folding of metal sheets are presented revealing that the material ruptured during the in-situ tensile tests along grain boundaries. Deformation twinning was observed in grains next to the crack indicating that the deformation processes must have originated from the grain boundaries.

scholarly journals A Flow Stress Model of 300M Steel for Isothermal Tension

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 252
Author(s):  
Rongchuang Chen ◽  
Shiyang Zhang ◽  
Xianlong Liu ◽  
Fei Feng
Keyword(s):  
Flow Stress ◽  
Constitutive Model ◽  
Tensile Deformation ◽  
Flow Behavior ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Model Parameters ◽  
Average Deviation ◽  
Cross Sectional ◽  
300M Steel

To investigate the effect of hot working parameters on the flow behavior of 300M steel under tension, hot uniaxial tensile tests were implemented under different temperatures (950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C) and strain rates (0.01 s−1, 0.1 s−1, 1 s−1, 10 s−1). Compared with uniaxial compression, the tensile flow stress was 29.1% higher because dynamic recrystallization softening was less sufficient in the tensile stress state. The ultimate elongation of 300M steel increased with the decrease of temperature and the increase of strain rate. To eliminate the influence of sample necking on stress-strain relationship, both the stress and the strain were calibrated using the cross-sectional area of the neck zone. A constitutive model for tensile deformation was established based on the modified Arrhenius model, in which the model parameters (n, α, Q, ln(A)) were described as a function of strain. The average deviation was 6.81 MPa (6.23%), showing good accuracy of the constitutive model.

Microstructure and Tensile Behavior of Ti-Rich Ti-Ni-Cu Melt-Spun Ribbon

2014 ◽  
Vol 936 ◽  
pp. 1163-1167
Author(s):  
Wen Jun He ◽  
Guang Hui Min ◽  
Oleg Tolochko
Keyword(s):  
Melt Spinning ◽  
Tensile Deformation ◽  
Amorphous Ribbon ◽  
Fracture Morphology ◽  
Tensile Tests ◽  
Tensile Fracture ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Annealed Ribbon ◽  
Martensitic State

Microstructure and mechanical properties of Ti51.5Ni25Cu23.5 ribbon fabricated by melt spinning were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and tensile tests. Some B19 martensite crystalline with (011) compound twin was embedded in the mainly amorphous ribbon, while the ribbon annealed at 450°C for 1 h is at fully martensitic state. Annealing process alter the preferential orientation from (022)-B19 to (111)-B19. Tensile fracture stresses of as-spun ribbon and the annealed ribbon are 1257 MPa and 250 MPa, respectively. The tensile fracture morphology of as-spun ribbon shows typical vein fringe while that of the annealed ribbon reveals fine but depth-inhomogeneous dimples. After tensile deformation, the annealed ribbon exhibits typical martensitic detwinning behavior accompanying with the strain contrast.

scholarly journals Study of the Microstructure and Crack Evolution Behavior of Al-5Fe-1.5Er Alloy

Materials ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 172 ◽  
Author(s):  
Ming Li ◽  
Zhiming Shi ◽  
Xiufeng Wu ◽  
Huhe Wang ◽  
Yubao Liu
Keyword(s):  
Electron Microscopy ◽  
Crack Initiation ◽  
Tensile Tests ◽  
Eutectic Structure ◽  
Interface Structure ◽  
X Ray ◽  
Transmission Electron ◽  
The Matrix ◽  
Evolution Behavior

In this work, the microstructure of Al-5Fe-1.5Er alloy was characterized and analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) techniques. The effect of microstructure on the behavior of crack initiation and propagation was investigated using in situ tensile testing. The results showed that when 1.5 wt.% Er was added in the Al-5Fe alloy, the microstructure consisted of α-Al matrix, Al3Fe, Al4Er, and Al3Fe + Al4Er eutectic phases. The twin structure of Al3Fe phase was observed, and the twin plane was {001}. Moreover, a continuous concave and convex interface structure of Al4Er was observed. Furthermore, Al3Fe was in the form of a sheet with a clear gap inside. In situ tensile tests of the alloy at room temperature showed that the crack initiation mainly occurred in the Al3Fe phase, and that the crack propagation modes included intergranular and trans-granular expansions. The crack trans-granular expansion was due to the strong binding between Al4Er phases and surrounding organization, whereas the continuous concave and convex interface structure of Al4Er provided a significant meshing effect on the matrix and the eutectic structure.

scholarly journals Thermoplastic elastomers containing 2D nanofillers: montmorillonite, graphene nanoplatelets and oxidized graphene platelets

2015 ◽  
Vol 17 (4) ◽  
pp. 74-81 ◽  
Author(s):  
Sandra Paszkiewicz ◽  
Iwona Pawelec ◽  
Anna Szymczyk ◽  
Zbigniew Rosłaniec
Keyword(s):  
Tensile Modulus ◽  
Thermoplastic Elastomer ◽  
Tensile Tests ◽  
Thermoplastic Elastomers ◽  
Graphene Nanoplatelets ◽  
Soft Phase ◽  
Permanent Set ◽  
Transmission Electron ◽  
Tetramethylene Oxide

Abstract This paper presents a comparative study on which type of platelets nanofiller, organic or inorganic, will affect the properties of thermoplastic elastomer matrix in the stronger manner. Therefore, poly(trimethylene terephthalate-block-poly(tetramethylene oxide) copolymer (PTT-PTMO) based nanocomposites with 0.5 wt.% of clay (MMT), graphene nanoplatelets (GNP) and graphene oxide (GO) have been prepared by in situ polymerization. The structure of the nanocomposites was characterized by transmission electron microscopy (TEM) in order to present good dispersion without large aggregates. It was indicated that PTT-PTMO/GNP composite shows the highest crystallization temperature. Unlike the addition of GNP and GO, the introduction of MMT does not have great effect on the glass transition temperature of PTMO-rich soft phase. An addition of all three types of nanoplatelets in the nanocomposites caused the enhancement in tensile modulus and yield stress. Additionally, the cyclic tensile tests showed that prepared nanocomposites have values of permanent set slightly higher than neat PTT-PTMO.

In Situ Transmission Electron Microscopy Investigation of the Deformation Behavior of Cu with Nanoscale Twins

2009 ◽  
Vol 633-634 ◽  
pp. 63-72 ◽  
Author(s):  
Y. B. Wang ◽  
M.L. Sui
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Deformation Behavior ◽  
Emission Sources ◽  
Dislocation Emission ◽  
Ultrahigh Strength ◽  
Transmission Electron ◽  
Microscopy Investigation ◽  
Electron Microscopy Investigation

This paper reviews our recent studies on the effect of twin boundary (TB) on the deformation behavior in Cu with nanoscale growth twins. In situ straining transmission electron microscopy investigations on TB migration, TBs and twin ends acting as dislocation emission sources, and the interactions between dislocations and TBs are highlighted. Results provide some useful understanding of why Cu with nanoscale twins leads to a combination of ultrahigh strength and high ductility.

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