Indentation-Induced Deformation Behavior in Martensitic Steel Observed through In Situ Nanoindentation in a Transmission Electron Microscopy

2006 ◽  
Vol 503-504 ◽  
pp. 239-244 ◽  
Author(s):  
Takahito Ohmura ◽  
A. Minor ◽  
Kaneaki Tsuzaki ◽  
J.W. Morris
Keyword(s):  
Grain Boundary ◽  
Deformation Behavior ◽  
Critical Stress ◽  
Martensitic Steel ◽  
High Angle ◽  
Block Boundary ◽  
Density Of Dislocations ◽  
Transmission Electron ◽  
Pile Up

Deformation behavior in the vicinity of grain boundary in Fe-0.4wt%C tempered martensitic steel were studied through in-situ nanoindentation in a TEM. Two types of boundaries were imaged in the dislocated martensitic structure: a low-angle lath boundary and a high-angle block boundary. In the case of a low-angle grain boundary, the dislocations induced by the indenter piled up against the boundary. As the indenter penetrated further, a critical stress appears to have been reached and a high density of dislocations was suddenly emitted on the far side of the grain boundary into the adjacent grain. In the case of the high-angle grain boundary, the numerous dislocations that were produced by the indentation were simply absorbed into the boundary, with no indication of pile-up or the transmission of strain.

Dislocation–grain boundary interactions in martensitic steel observed through in situ nanoindentation in a transmission electron microscope

2004 ◽  
Vol 19 (12) ◽  
pp. 3626-3632 ◽  
Author(s):  
T. Ohmura ◽  
A.M. Minor ◽  
E.A. Stach ◽  
J.W. Morris
Keyword(s):  
Electron Microscope ◽  
Grain Boundary ◽  
Transmission Electron Microscope ◽  
Critical Stress ◽  
Martensitic Steel ◽  
High Angle ◽  
Block Boundary ◽  
Density Of Dislocations ◽  
Transmission Electron

Dislocation–interface interactions in Fe–0.4 wt% C tempered martensitic steel were studied through in situ nanoindentation in a transmission electron microscope (TEM). Two types of boundaries were imaged in the dislocated martensitic structure: a low-angle (probable) lath boundary and a coherent, high-angle (probable) block boundary. In the case of a low-angle grain boundary, the dislocations induced by the indenter piled up against the boundary. As the indenter penetrated further, a critical stress appeared to have been reached, and a high density of dislocations was suddenly emitted on the far side of the grain boundary into the adjacent grain. In the case of the high-angle grain boundary, the numerous dislocations that were produced by the indentation were simply absorbed into the boundary, with no indication of pileup or the transmission of strain. This surprising observation is interpreted on the basis of the crystallography of the block boundary.

Study of Deformation Behavior of Ultrafine-grained Materials Through in Situ Nanoindentation in a Transmission Electron Microscope

2005 ◽  
Vol 20 (7) ◽  
pp. 1735-1740 ◽  
Author(s):  
M. Jin ◽  
A.M. Minor ◽  
D. Ge ◽  
J.W. Morris
Keyword(s):  
Electron Microscope ◽  
Grain Boundary ◽  
Transmission Electron Microscope ◽  
Deformation Behavior ◽  
Boundary Migration ◽  
Boundary Motion ◽  
Transmission Electron ◽  
Ultrafine Grained ◽  
Grain Boundary Motion

The mechanical properties of ultrafine-grained and nanograined materials have received a great deal of recent attention because of their unusual and promising values. However, some of the most important mechanisms of deformation remain unclear. In this work, the deformation behavior of ultrafine-grained Al films and ultrafine-grained Fe is studied through in situ nanoindentation in a transmission electron microscope. Deformation-induced coarsening by grain boundary migration was observed in the ultrafine-grained Al films during deformation at room temperature, whereas no grain boundary motion was found in ultrafine-grained Fe. The lack of grain boundary motion in Fe was attributed to the pinning effect of nano-sized particles at the Fe grain boundaries.

In-Situ Quasi-Real Time Observations of the Deformation of α-Brass Bicrystals via Synchrotron X-Ray Topography

1993 ◽  
Vol 307 ◽  
Author(s):  
Z. Zeng ◽  
Z. Rek ◽  
J. C. Bilello
Keyword(s):  
Grain Boundary ◽  
Real Time ◽  
Deformation Behavior ◽  
Critical Value ◽  
X Ray Diffraction ◽  
X Ray ◽  
Pile Up ◽  
Schmid Factor

ABSTRACTReal-time studies of the deformation behavior of a-brass bicrystals were conducted via in-situ synchrotron white beam X-ray topography (SWBXRT). The object of this work was to understand the role of internal interfaces such as grain boundaries, in controlling the mechanical behavior of materials. A brass bicrystal, in which the two grains made 5° of tilt and 11° of twist with respect to each other was grown by the Bridgman method. Observations were performed by straining the bicrystal in a microtensile stage while stop-action X-ray diffraction topographs were taken. Slip initiated in the grain with the most favorable Schmid factor at a stress level of 1.4MPa which was 5% of the macroyield stress. Since the grain boundary acted as a barrier to slip, the next grain did not slip until the dislocation pile-up at the grain boundary reached a critical value.

Motion of Crystal/Crystal and Crystal/Amorphous Interfaces

1990 ◽  
Vol 183 ◽  
Author(s):  
J. L. Batstone
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Temperature ◽  
Grain Boundary ◽  
Boundary Motion ◽  
High Temperature Annealing ◽  
Thermally Activated ◽  
Transmission Electron ◽  
Grain Boundary Motion

AbstractMotion of ordered twin/matrix interfaces in films of silicon on sapphire occurs during high temperature annealing. This process is shown to be thermally activated and is analogous to grain boundary motion. Motion of amorphous/crystalline interfaces occurs during recrystallization of CoSi2 and NiSi2 from the amorphous phase. In-situ transmission electron microscopy has revealed details of the growth kinetics and interfacial roughness.

Simulation of the interaction of plastic zone dislocations with the grain boundary at brittle-plastic transition temperatures in molybdenum

2021 ◽  
Vol 2021 (3) ◽  
pp. 77-85
Author(s):  
K. M. Borysovska ◽  
◽  
N. M. Marchenko ◽  
Yu. M. Podrezov ◽  
S. O. Firstov ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Grain Boundary ◽  
Plastic Zone ◽  
Grain Boundaries ◽  
Crack Tip ◽  
Dynamics Simulation ◽  
Density Of Dislocations ◽  
Grain Sizes ◽  
Pile Up

The (DD) method was used to model the formation of the plastic zone of the top of the cracks in polycrystalline molybdenum. Special attention was paid to take into account the interaction of dislocations in the plastic zone with grain boundaries. Structural sensitivity of fracture toughness was analyzed under brittle-ductile condition. Simulations were performed for a range of grain sizes from 400 to 100 μm, at which a sudden increase in fracture toughness with a decrease of grain size was experimentally shown. We calculated the value of K1c taking into account the shielding action of dislocations. The position of all dislocations in the plastic zone at fracture moment was calculated. Based on these data, we obtained the dependences of dislocation density on the distance from the crack tip thereby confirming significant influence of the grain boundaries on plastic zone formation. At large grain sizes, when the plastic zone does not touch the boundary, the distribution of dislocations remained unchanged. As grains reduce their size to size of the plastic zone, they start formating a dislocation pile – up near the boundaries. Dislocations on plastic zone move slightly toward the crack tip, but the density of dislocations in the middle of the grain remains unchanged, and fracture toughness remains almost unchanged. Further reduction of the grain size leads to the Frank-Reed source activation on the grain boundary Forming dislocation pile-up of the neighbor grains. Its stress concentration acts on dislocations of the first grain and causes redistribution of plastic zone dislocations. If the reduction in grain size is not enough to form a strong pile-up, density of dislocations on plastic zone increases slightly and crack resistance increases a few percent. Further reduction of grains promotes strong pile-up, dislocations move to crack tip, and its density on plastic zone increases. Crack is shielded and fracture toughness increases sharply. The calculation showed that the fracture toughness jump is observed at grain sizes of 100—150 μm, in good agreement with the experiment. Keywords: dislocation dynamics simulation, molybdenum, fracture toughness, grain size, plastic zone, brittle-ductile transition.

scholarly journals In situ atomic scale mechanisms of strain-induced twin boundary shear to high angle grain boundary in nanocrystalline Pt

2018 ◽  
Vol 195 ◽  
pp. 69-73 ◽  
Author(s):  
Lihua Wang ◽  
Jiao Teng ◽  
Yu Wu ◽  
Xuechao Sha ◽  
Sisi Xiang ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Twin Boundary ◽  
Atomic Scale ◽  
High Angle ◽  
Boundary Shear

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.

scholarly journals Accommodation of large plastic strains and defect accumulation in nanocrystalline Ni grains

2007 ◽  
Vol 22 (8) ◽  
pp. 2241-2253 ◽  
Author(s):  
X.L. Wu ◽  
E. Ma
Keyword(s):  
Deformation Behavior ◽  
Boundary Migration ◽  
Temperature Deformation ◽  
Plastic Strains ◽  
Domain Structures ◽  
Transmission Electron ◽  
Defect Accumulation ◽  
Pile Up ◽  
Slip Planes ◽  
The Stability

A transmission electron microscopy (TEM) study has been carried out to uncover how dislocations and twins accommodate large plastic strains and accumulate in very small nanocrystalline Ni grains during low-temperature deformation. We illustrate dislocation patterns that suggest preferential deformation and nonuniform defect storage inside the nanocrystalline grain. Dislocations are present in individual and dipole configurations. Most dislocations are of the 60° type and pile up on (111) slip planes. Various deformation responses, in the forms of dislocations and twinning, may simultaneously occur inside a nanocrystalline grain. Evidence for twin boundary migration has been obtained. The rearrangement and organization of dislocations, sometimes interacting with the twins, lead to the formation of subgrain boundaries, subdividing the nanograin into mosaic domain structures. The observation of strain (deformation)-induced refinement contrasts with the recently reported stress-assisted grain growth in nanocrystalline metals and has implications for understanding the stability and deformation behavior of these highly nonequilibrium materials.

Observations and implications of grain boundary dislocation networks in high-angle YBa2Cu3O7−δ grain boundaries

1990 ◽  
Vol 5 (5) ◽  
pp. 919-928 ◽  
Author(s):  
S. E. Babcock ◽  
D. C. Larbalestier
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Weak Link ◽  
Coincidence Site Lattice ◽  
Boundary Structure ◽  
High Angle ◽  
Grain Boundary Structure ◽  
Transmission Electron ◽  
Means Of Transmission ◽  
Regular Networks

Regular networks of localized grain boundary dislocations (GBDs) have been imaged by means of transmission electron microscopy in three different types of high-angle grain boundaries in YBa2Cu3O7-δ, implying that these boundaries possess ordered structures upon which a significant periodic strain field is superimposed. The occurrence of these GBD networks is shown to be consistent with the GBD/Structural Unit and Coincidence Site Lattice (CSL)/Near CSL descriptions for grain boundary structure. Thus, these dislocations appear to be intrinsic features of the boundary structure. The spacing of the observed GBDs ranged from ∼10 nm to ∼100 nm. These GBDs make the grain boundaries heterogeneous on a scale that approaches the coherence length and may contribute to their weak-link character by producing the “superconducting micro-bridge” microstructure which has been suggested on the basis of detailed electromagnetic measurements on similar samples.

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