scholarly journals Critical assessment of hydrogen effects on the slip transmission across grain boundaries in α -Fe

2016 ◽  
Vol 472 (2185) ◽  
pp. 20150617 ◽  
Author(s):  
I. Adlakha ◽  
K. N. Solanki
Keyword(s):  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Energy Barrier ◽  
Strain Energy ◽  
Strengthening Mechanism ◽  
Dislocation Motion ◽  
Dislocation Network ◽  
Mode Transition ◽  
Slip Transmission

Grain boundaries (GBs) play a fundamental role in the strengthening mechanism of crystalline structures by acting as an impediment to dislocation motion. However, the presence of an aggressive environment such as hydrogen increases the susceptibility to intergranular fracture. Further, there is a lack of systematic investigations exploring the role of hydrogen on the dislocation–grain-boundary (DGB) interactions. Thus, in this work, the effect of hydrogen on the interactions between a screw dislocation and 〈111〉 tilt GBs in α -Fe were examined. Our simulations reveal that the outcome of the DGB interaction strongly depends on the underlying GB dislocation network. Further, there exists a strong correlation between the GB energy and the energy barrier for slip transmission. In other words, GBs with lower interfacial energy demonstrate a higher barrier for slip transmission. The introduction of hydrogen along the GB causes the energy barrier for slip transmission to increase consistently for all of the GBs examined. The energy balance for a crack initiation in the presence of hydrogen was examined with the help of our observations and previous findings. It was found that the presence of hydrogen increases the strain energy stored within the GB which could lead to a transgranular-to-intergranular fracture mode transition.

scholarly journals The Role of Slip Transmission on Plastic Strain accumulationacross Grain Boundaries

2012 ◽  
Vol 4 ◽  
pp. 169-178 ◽  
Author(s):  
Wael Abuzaid ◽  
Michael D. Sangid ◽  
Huseyin Sehitoglu ◽  
Jay Carroll ◽  
John Lambros
Keyword(s):  
Plastic Strain ◽  
Grain Boundaries ◽  
Slip Transmission

High Toughness Alumina/Aluminate: The Role Of Hetero-Interfaces

1995 ◽  
Vol 409 ◽  
Author(s):  
M. E. Brito ◽  
M. Yasuoka ◽  
S. Kanzaki
Keyword(s):  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Fracture Mode ◽  
Auger Electron ◽  
High Strength ◽  
Interfacial Debonding ◽  
Amorphous Phases ◽  
High Toughness ◽  
Interface Structures

AbstractSilica doped alumina/aluminate materials present a combination of high strength and high toughness not achieved before in other alumina systems, except for transformation toughened alumina. We have associated the increase in toughness to crack bridging by anisotropically grown alumina grains with concurrent interfacial debonding of these grains. A HREM study of grain boundaries and hetero-interface structures in this material shows the absence of amorphous phases at grain boundaries. Local Auger electron analysis of fractured surfaces revealed the coexistence of Si and La at the grain facets exposed by the noticeable intergranular fracture mode of this material. It is concluded that a certain and important degree of boundaries weakness is related to both, presence of Si at the interfaces and existence of alumina/aluminate hetero-interfaces.

Barriers to Strain Relaxation in Epitaxial Fluorides on Si(111)

1993 ◽  
Vol 308 ◽  
Author(s):  
Weidan Li ◽  
Steve Hymes ◽  
Shyam P. Murarka ◽  
Leo J. Schowalter
Keyword(s):  
Plastic Deformation ◽  
Temperature Dependence ◽  
Mechanical Stress ◽  
Temperature Change ◽  
Energy Barrier ◽  
Strain Energy ◽  
Strain Relaxation ◽  
Dislocation Motion ◽  
Unusual Behavior ◽  
Increasing Temperature

ABSTRACTThe mechanical stress of epitaxial SrF2 and CaF2 films on Si(111) substrates has been measured as a function of temperature by the substrate curvature technique. The temperature dependence of the stress in the SrF2 film is interpreted in terms of an energy barrier to dislocation motion. When the strain energy is smaller than the value needed to overcome the barrier, the change in stress is due mainly to elastic deformation. As the temperature change increases, the strain energy becomes large enough to overcome the barrier, at which point plastic deformation initiates. Unlike SrF2, the stress behavior of the CaF2 film for increasing temperature is quite different from its behavior for decreasing temperature. This unusual behavior is not understood at this time.

scholarly journals The Role of Grain Boundary Precipitates during Intergranular Fracture in 6xxx Series Aluminium Alloys

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 894
Author(s):  
Inga G. Ringdalen ◽  
Ingvild J. T. Jensen ◽  
Calin D. Marioara ◽  
Jesper Friis
Keyword(s):  
Tensile Strength ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Aluminium Alloys ◽  
Density Functional ◽  
Tensile Tests ◽  
Free Zone ◽  
Transmission Electron

During ageing, 6xxx aluminium alloys will develop a microstructure characterised by needle-shaped Mg/Si-rich precipitates in the bulk, precipitate-free zones along the grain boundaries and larger Mg/Si-rich precipitates on the grain boundary. Depending on, among other things, the size of the precipitate-free zone, these alloys are prone to intergranular fracture. The role of the grain boundary precipitates during the initiation and propagation of the intergranular fracture is still not fully understood. Transmission Electron Microscopy has been used to characterise the grain boundaries and grain boundary precipitates. The precipitates were found to be of the β′ type surrounded by a layer of U2 structure. The atomic details of relevant interfaces of Al-β′ were characterised for further investigation. Density Functional Theory simulations were performed on the bulk precipitate structures and on the interfaces obtained experimentally. The decohesion energy of these interfaces was calculated and compared to bulk values. In addition, simulated tensile tests were performed in order to find values for the tensile strength σt. The dependence of the interfacial energy and tensile strength of β′ grain boundary precipitates were found to depend on the orientation and type of interface in addition to the amount of defects on the interface.

Elucidation of block boundaries as the dissolution channels in hydrated cement

1978 ◽  
Vol 36 (1) ◽  
pp. 484-485
Author(s):  
N.V. Belov ◽  
U.I. Papiashwili ◽  
B.E. Yudovich
Keyword(s):  
Liquid Phase ◽  
Grain Boundaries ◽  
Benzoyl Peroxide ◽  
Phase Contrast ◽  
Active Role ◽  
Point Of View ◽  
Hardened Cement ◽  
Hydrated Cement ◽  
Hardened Cement Paste

It has been almost universally adopted that dissolution of solids proceeds with development of uniform, continuous frontiers of reaction.However this point of view is doubtful / 1 /. E.g. we have proved the active role of the block (grain) boundaries in the main phases of cement, these boundaries being the areas of hydrate phases' nucleation / 2 /. It has brought to the supposition that the dissolution frontier of cement particles in water is discrete. It seems also probable that the dissolution proceeds through the channels, which serve both for the liquid phase movement and for the drainage of the incongruant solution products. These channels can be appeared along the block boundaries.In order to demonsrate it, we have offered the method of phase-contrast impregnation of the hardened cement paste with the solution of methyl metacrylahe and benzoyl peroxide. The viscosity of this solution is equal to that of water.

Carbide precipitation and chromium depletion on coherent twin boundaries in deformed 304 stainless steels

1992 ◽  
Vol 50 (2) ◽  
pp. 1216-1217
Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D.J. Matlock ◽  
W.W. Fisher ◽  
P.M. Tarin ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Stainless Steels ◽  
Interfacial Free Energy ◽  
Carbide Precipitation ◽  
Twin Boundaries ◽  
Invariant Structure ◽  
Heat Treated ◽  
Constant Structure ◽  
Cr Depletion

Coherent annealing-twin boundaries are constant structure and energy interfaces with an average interfacial free energy of ∼19mJ/m2 versus ∼210 and ∼835mJ/m2 for incoherent twins and “regular” grain boundaries respectively in 304 stainless steels (SS). Due to their low energy, coherent twins form carbides about a factor of 100 slower than grain boundaries, and limited work has also shown differences in Cr-depletion (sensitization) between twin versus grain boundaries. Plastic deformation, may, however, alter the kinetics and thermodynamics of twin-sensitization which is not well understood. The objective of this work was to understand the mechanisms of carbide precipitation and Cr-depletion on coherent twin boundaries in deformed SS. The research is directed toward using this invariant structure and energy interface to understand and model the role of interfacial characteristics on deformation-induced sensitization in SS. Carbides and Cr-depletion were examined on a 20%-strain, 0.051%C-304SS, heat treated to 625°C-4.5h, as described elsewhere.

Morphology and atomic structure of segregated grain boundaries in Cu-Sb

1992 ◽  
Vol 50 (1) ◽  
pp. 254-255
Author(s):  
R. W. Fonda ◽  
D. E. Luzzi
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Atomic Structure ◽  
Copper Alloys ◽  
Polycrystalline Materials ◽  
Grain Boundary Embrittlement ◽  
Boundary Embrittlement

The properties of polycrystalline materials are strongly dependant upon the strength of internal boundaries. Segregation of solute to the grain boundaries can adversely affect this strength. In copper alloys, segregation of either bismuth or antimony to the grain boundary will embrittle the alloy by facilitating intergranular fracture. Very small quantities of bismuth in copper have long been known to cause severe grain boundary embrittlement of the alloy. The effect of antimony is much less pronounced and is observed primarily at lower temperatures. Even though moderate amounts of antimony are fully soluble in copper, concentrations down to 0.14% can cause grain boundary embrittlement.

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