Relative mobility of screw versus edge dislocations controls the ductile-to-brittle transition in metals

2021 ◽  
Vol 118 (37) ◽  
pp. e2110596118
Author(s):  
Yan Lu ◽  
Yu-Heng Zhang ◽  
En Ma ◽  
Wei-Zhong Han
Keyword(s):  
Dislocation Nucleation ◽  
Dislocation Velocity ◽  
Relative Mobility ◽  
Dislocation Source ◽  
Cubic Metals ◽  
Brittle Transition ◽  
Ductile To Brittle Transition ◽  
Potential Factors ◽  
Dislocation Sources ◽  
Edge Dislocations

Body-centered cubic metals including steels and refractory metals suffer from an abrupt ductile-to-brittle transition (DBT) at a critical temperature, hampering their performance and applications. Temperature-dependent dislocation mobility and dislocation nucleation have been proposed as the potential factors responsible for the DBT. However, the origin of this sudden switch from toughness to brittleness still remains a mystery. Here, we discover that the ratio of screw dislocation velocity to edge dislocation velocity is a controlling factor responsible for the DBT. A physical model was conceived to correlate the efficiency of Frank–Read dislocation source with the relative mobility of screw versus edge dislocations. A sufficiently high relative mobility is a prerequisite for the coordinated movement of screw and edge segments to sustain dislocation multiplication. Nanoindentation experiments found that DBT in chromium requires a critical mobility ratio of 0.7, above which the dislocation sources transition from disposable to regeneratable ones. The proposed model is also supported by the experimental results of iron, tungsten, and aluminum.

scholarly journals The nucleation of the Izmit and Düzce earthquakes: Some mechanical logic on where and how ruptures began

2021 ◽  
Author(s):  
Michel Bouchon ◽  
Hayrullah Karabulut ◽  
Mustafa Aktar ◽  
Serdar Özalaybey ◽  
Jean Schmittbuhl ◽  
...  
Keyword(s):  
Strike Slip ◽  
Seismic Events ◽  
Fault Geometry ◽  
Brittle Transition ◽  
The North ◽  
Impending Rupture ◽  
Natural Tendency ◽  
Ductile To Brittle Transition ◽  
Mechanical Logic ◽  
Rupture Speed

Summary In spite of growing evidence that many earthquakes are preceded by increased seismic activity, the nature of this activity is still poorly understood. Is it the result of a mostly random process related to the natural tendency of seismic events to cluster in time and space, in which case there is little hope to ever predict earthquakes? Or is it the sign that a physical process that will lead to the impending rupture has begun, in which case we should attempt to identify this process. With this aim we take a further look at the nucleation of two of the best recorded and documented strike-slip earthquakes to date, the 1999 Izmit and Düzce earthquakes which ruptured the North Anatolian Fault over ∼200 km. We show the existence of a remarkable mechanical logic linking together nucleation characteristics, stress loading, fault geometry and rupture speed. In both earthquakes the observations point to slow aseismic slip occurring near the ductile-to-brittle transition zone as the motor of their nucleation.

scholarly journals Probing the Statistical Validity of the Ductile-to-Brittle Transition in Metallic Nanowires Using GPU Computing

2013 ◽  
Vol 9 (12) ◽  
pp. 5558-5566 ◽  
Author(s):  
William R. French ◽  
Amulya K. Pervaje ◽  
Andrew P. Santos ◽  
Christopher R. Iacovella ◽  
Peter T. Cummings
Keyword(s):  
Gpu Computing ◽  
Metallic Nanowires ◽  
Brittle Transition ◽  
Statistical Validity ◽  
Ductile To Brittle Transition

scholarly journals Fracture and Ductile-to-Brittle Transition Characteristics of Molybdenum by Impact and Static Bend Tests

1995 ◽  
Vol 36 (4) ◽  
pp. 504-510 ◽  
Author(s):  
Yutaka Hiraoka ◽  
Hiroaki Kurishita ◽  
Minoru Narui ◽  
Hideo Kayano
Keyword(s):  
Brittle Transition ◽  
Bend Tests ◽  
Ductile To Brittle Transition

Effects of thermal treatments on the ductile to brittle transition of MANET steel

1996 ◽  
Vol 233-237 ◽  
pp. 248-252 ◽  
Author(s):  
P. Gondi ◽  
R. Montanari ◽  
A. Sili ◽  
M.E. Tata
Keyword(s):  
Thermal Treatments ◽  
Brittle Transition ◽  
Ductile To Brittle Transition

Study of Ductile-to-Brittle Transition in Single Grit Diamond Scribing of Silicon: Application to Wire Sawing of Silicon Wafers

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Hao Wu ◽  
Shreyes N. Melkote
Keyword(s):  
Hydrostatic Pressure ◽  
Silicon Wafers ◽  
Depth Of Cut ◽  
Critical Depth ◽  
External Hydrostatic Pressure ◽  
Tensile Stresses ◽  
Brittle Transition ◽  
Ductile Mode Cutting ◽  
Critical Depth Of Cut ◽  
Ductile To Brittle Transition

The ductile-to-brittle cutting mode transition in single grit diamond scribing of monocrystalline silicon is investigated in this paper. Specifically, the effects of scriber tip geometry, coefficient of friction, and external hydrostatic pressure on the critical depth of cut associated with ductile-to-brittle transition and crack generation are studied via an eXtended Finite Element Method (XFEM) based model, which is experimentally validated. Scribers with a large tip radius are shown to produce lower tensile stresses and a larger critical depth of cut compared with scribers with a sharp tip. Spherical tipped scribers are shown to generate only surface cracks, while sharp tipped scribers (conical, Berkovich and Vickers) are found to create large subsurface tensile stresses, which can lead to nucleation of subsurface median/lateral cracks. Lowering the friction coefficient tends to increase the critical depth of cut and hence the extent of ductile mode cutting. The results also show that larger critical depth of cut can be obtained under external hydrostatic pressure. This knowledge is expected to be useful in optimizing the design and application of the diamond coated wire employed in fixed abrasive diamond wire sawing of photovoltaic silicon wafers.

Dislocation Nucleation and Growth in MOCVD GaN/AlN Films on Stepped and Step-free 4H-SiC Mesa Substrates

2008 ◽  
Vol 1090 ◽  
Author(s):  
Mark E. Twigg ◽  
Yoosuf N. Picard ◽  
Nabil D. Bassim ◽  
Joshua D. Caldwell ◽  
Michael A. Mastro ◽  
...  
Keyword(s):  
Dominant Role ◽  
High Stress ◽  
Chemical Vapor ◽  
Misfit Strain ◽  
Nucleation And Growth ◽  
Dislocation Nucleation ◽  
Threading Dislocations ◽  
Surface Steps ◽  
Half Loop ◽  
Edge Dislocations

AbstractUsing transmission electron microscopy, we have analyzed dislocations in AlN nucleation layers and GaN films grown by metallorganic chemical vapor deposition (MOCVD) on the (0001) surface of epitaxially-grown 4H-SiC mesas with and without steps. For 4H-SiC substrates free of SiC surface steps, half-loop nucleation and glide parallel to the AlN/SiC interfacial plane play the dominant role in strain relief, with no mechanism for generating threading dislocations. In contrast, 4H-SiC mesa surfaces with steps give rise to regions of high stress at the heteroepitaxial interface, thereby providing an environment conducive to the nucleation and growth of threading dislocations, which act to accommodate misfit strain by the tilting of threading edge dislocations.

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