scholarly journals Super Ductility of Nanoglass Aluminium Nitride

Nanomaterials ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1535 ◽  
Author(s):  
Zhao ◽  
Peng ◽  
Huang ◽  
Yang ◽  
Hu ◽  
...  
Keyword(s):  
Strain Rate ◽  
Ultimate Strength ◽  
Scaling Law ◽  
Aluminium Nitride ◽  
Grain Sizes ◽  
Shear Transformation ◽  
Effects Of Temperature ◽  
Shear Transformation Zones ◽  
Function Relationship ◽  
Dynamics Simulations

Ceramics have been widely used in many fields because of their distinctive properties, however, brittle fracture usually limits their application. To solve this problem, nanoglass ceramics were developed. In this article, we numerically investigated the mechanical properties of nanoglass aluminium nitride (ng-AlN) with different glassy grain sizes under tension using molecular dynamics simulations. It was found that ng-AlN exhibits super ductility and tends to deform uniformly without the formation of voids as the glassy grain size decreases to about 1 nm, which was attributed to a large number of uniformly distributed shear transformation zones (STZs). We further investigated the effects of temperature and strain rate on ng-AlNd = 1 nm, which showed that temperature insignificantly influences the elastic modulus, while the dependence of the ultimate strength on temperature follows the T2/3 scaling law. Meanwhile, the ultimate strength of ng-AlNd = 1 nm is positively correlated with the strain rate, following a power function relationship.

Effects of Temperature and Strain Rate on Compressive Mechanical Properties of Ultrafine-Grained CP Titanium

2007 ◽  
Vol 26-28 ◽  
pp. 381-384 ◽  
Author(s):  
Zhi Guo Fan ◽  
Chao Ying Xie
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Ultimate Strength ◽  
Room Temperature ◽  
Equal Channel Angular Extrusion ◽  
Coarse Grain ◽  
Ultrafine Grained ◽  
Effects Of Temperature ◽  
Cp Ti ◽  
Compressive Tests

Ultrafine-grained (UFG) CP Ti were successfully prepared by Equal Channel Angular Extrusion (ECAE) at 390°C~400°C, small than 0.5 um in size. The compressive tests for coarse grain (CG) and UFG Ti were carried out at room temperature (RT) and 77K. UFG Ti showed excellent ductility and higher strength than CG Ti at RT and 77 K. The strain hardening of UFG Ti was improved at 77 K. The compressive ultimate strengths of CG Ti and UFG Ti were both enhanced as the strain rate increased, but CG Ti showed more obvious temperature and strain rate dependence of flow stress, comparing with UFG Ti. When the strain rate increased to 1×10-1/s, the compressive ultimate strength of UFG Ti was kept almost constant, while the ultimate strength of CG Ti increased to the strength level of UFG Ti.

From Crystalline to Glassy: Crack Propagation Modes in Decagonal Quasicrystals

2003 ◽  
Vol 805 ◽  
Author(s):  
Christoph Rudhart ◽  
Peter Gumbsch ◽  
Hans-Rainer Trebin
Keyword(s):  
Crack Extension ◽  
Amorphous Solids ◽  
Linear Scaling ◽  
Dislocation Emission ◽  
Medium Temperature ◽  
Decagonal Quasicrystals ◽  
Shear Transformation ◽  
Shear Transformation Zones ◽  
Dynamics Simulations ◽  
Increasing Temperature

ABSTRACTThe propagation of mode-I cracks in a two-dimensional decagonal model quasicrystal is studied by molecular dynamics simulations. The samples are endowed with an atomically sharp seed crack and a temperature gradient. Subsequently the crack is loaded by linear scaling of the displacement field. The response of the crack running into regions of increasing temperature is monitored.For low temperatures below 30% of the melting temperature Tm the model-quasicrystal fails by brittle fracture. We observe that the crack follows the path of dislocations nucleated at its tip. The crack propagates along well defined planes and circumvents tightly bound clusters. In the medium temperature regime from 30% to 70% Tm the crack is blunting spontaneously by dislocation emission. In the range of 70%-80% Tm the quasicrystal fails by nucleation, growth and coalescence of micro-voids. This gradual, dislocation-free crack extension is caused by plastic deformation which is mediated by localized rearrangements comparable to so-called shear transformation zones in amorphous solids.

scholarly journals Effect of Annealing on Strain Rate Sensitivity of Metallic Glass under Nanoindentation

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1063
Author(s):  
Mingcan Li
Keyword(s):  
Mechanical Properties ◽  
Metallic Glass ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Annealing Time ◽  
Isothermal Annealing ◽  
Rate Sensitivity ◽  
Underlying Mechanism ◽  
Shear Transformation ◽  
Shear Transformation Zones

The influence of isothermal annealing on the strain rate sensitivity (SRS) of a Zr-based bulk metallic glass (BMG) was investigated by nanoindentation. A more positive SRS is observed with a decrease in the content of the free volume (FV) of the sample. Furthermore, the SRS becomes nearly constant with increasing annealing time when the FV is annealed out. By taking into consideration the FV-assisted activation and combination of the shear transformation zones (STZs), the underlying mechanism is well understood. The current work may offer useful insights into the correlation between the microstructure and mechanical properties of BMGs.

scholarly journals Collisions between amorphous carbon nanoparticles: phase transformations

2020 ◽  
Vol 641 ◽  
pp. A159
Author(s):  
Maureen L. Nietiadi ◽  
Felipe Valencia ◽  
Rafael I. Gonzalez ◽  
Eduardo M. Bringa ◽  
Herbert M. Urbassek
Keyword(s):  
Amorphous Carbon ◽  
Contact Radius ◽  
Central Collisions ◽  
Dust Clouds ◽  
Collision Zone ◽  
Atomic Surface ◽  
Shear Transformation ◽  
Shear Transformation Zones ◽  
Dynamics Simulations ◽  
20 Nm

Context. Collisions of nanoparticles (NPs) occur in dust clouds and protoplanetary disks. Aims. Sticking collisions lead to the growth of NPs, in contrast to bouncing or even fragmentation events and we aim to explore these processes in amorphous carbon NPs. Methods. Using molecular-dynamics simulations, we studied central collisions between amorphous carbon NPs that had radii in the range of 6.5–20 nm and velocities of 100–3000 m s−1, and with varying sp3 content (20–55%). Results. We find that the collisions are always sticking. The contact radius formed surpasses the estimate provided by the traditional Johnson-Kendall-Roberts model, pointing at the dominant influence of attractive forces between the NPs. Plasticity occurs via shear-transformation zones. In addition, we find bond rearrangements in the collision zone. Low-sp3 material (sp3 ≤ 40%) is compressed to sp3 > 50%. On the other hand, for the highest sp3 fraction, 55%, graphitization starts in the collision zone leading to low-density and even porous material. Conclusions. Collisions of amorphous carbon NPs lead to an increased porosity, atomic surface roughness, and changed hybridization that affect the mechanical and optical properties of the collided NPs.

scholarly journals Influence of grain size and composition, topology and excess free volume on the deformation behavior of Cu–Zr nanoglasses

2015 ◽  
Vol 6 ◽  
pp. 537-545 ◽  
Author(s):  
Daniel Şopu ◽  
Karsten Albe
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Free Volume ◽  
Deformation Behavior ◽  
Alloy Composition ◽  
Topological Order ◽  
Shear Transformation ◽  
Shear Transformation Zones ◽  
Dynamics Simulations ◽  
Topological Disorder

The influence of grain size and composition on the mechanical properties of Cu–Zr nanoglasses (NGs) is investigated by molecular dynamics simulations using two model glasses of different alloy composition, namely Cu64Zr36 (Cu-rich) and Cu36Zr64 (Zr-rich). When the grain size is increased, or the fraction of interfaces in these NGs is decreased, we find a transition from a homogeneous to an inhomogeneous plastic deformation, because the softer interfaces are promoting the formation shear transformation zones. In case of the Cu-rich system, shear localization at the interfaces is most pronounced, since both the topological order and free volume content of the interfaces are very different from the bulk phase. After thermal treatment the redistribution of free volume leads to a more homogenous deformation behavior. The deformation behavior of the softer Zr-rich nanoglass, in contrast, is only weakly affected by the presence of glass–glass interfaces, since the interfaces don’t show topological disorder. Our results provide clear evidence that the mechanical properties of metallic NGs can be systematically tuned by controlling the size and the chemical composition of the glassy nanograins.

High Temperature Deformation Mechanism Maps of NiAl

2004 ◽  
Vol 449-452 ◽  
pp. 57-60
Author(s):  
I.G. Lee ◽  
A.K. Ghosh
Keyword(s):  
High Temperature ◽  
Strain Rate ◽  
Deformation Mechanism ◽  
Calculation Method ◽  
Deformation Behavior ◽  
Tensile Tests ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Grain Sizes ◽  
Temperature Strain

In order to analyze high temperature deformation behavior of NiAl alloys, deformation maps were constructed for stoichiometric NiAl materials with grain sizes of 4 and 200 µm. Relevant constitute equations and calculation method will be described in this paper. These maps are particularly useful in identifying the location of testing domains, such as creep and tensile tests, in relation to the stress-temperature-strain rate domains experienced by NiAl.

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