scholarly journals Shear Deformation Helps Phase Transition in Pure Iron Thin Films with “Inactive” Surfaces: A Molecular Dynamics Study

Crystals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 855
Author(s):  
Ting Ruan ◽  
Binjun Wang ◽  
Chun Xu ◽  
Yunqiang Jiang
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Molecular Dynamics ◽  
Free Surface ◽  
Phase Transitions ◽  
Shear Deformation ◽  
Dynamics Simulation ◽  
Nanoscale Systems ◽  
Free Surfaces ◽  
Nucleation Sites

In a previous study, it was shown that the (111)fcc, (110)fcc and (111)bcc free surfaces do not assist the phase transitions as nucleation sites upon heating/cooling in iron (Fe) thin slabs. In the present work, the three surfaces are denoted as “inactive” free surfaces. The phase transitions in Fe thin films with these “inactive” free surfaces have been studied using a classical molecular dynamics simulation and the Meyer–Entel potential. Our results show that shear deformation helps to activate the free surface as nucleation sites. The transition mechanisms are different in dependence on the surface orientation. In film with the (111)fcc free surface, two body-centered cubic (bcc) phases with different crystalline orientations nucleate at the free surface. In film with the (110)fcc surface, the nucleation sites are the intersections between the surfaces and stacking faults. In film with the (111)bcc surface, both heterogeneous nucleation at the free surface and homogeneous nucleation in the bulk material are observed. In addition, the transition pathways are analyzed. In all cases studied, the unstrained system is stable and no phase transition takes place. This work may be helpful to understand the mechanism of phase transition in nanoscale systems under external deformation.

scholarly journals Phase Transition in Iron Thin Films Containing Coherent Twin Boundaries: A Molecular Dynamics Approach

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3631 ◽  
Author(s):  
Binjun Wang ◽  
Yunqiang Jiang ◽  
Chun Xu
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Molecular Dynamics ◽  
Free Surface ◽  
Transition Temperature ◽  
Film Thickness ◽  
Martensitic Phase ◽  
Martensitic Transition ◽  
Twin Boundaries ◽  
Martensitic Phase Transition

Using molecular dynamics (MD) simulation, the austenitic and martensitic phase transitions in pure iron (Fe) thin films containing coherent twin boundaries (TBs) have been studied. Twelve thin films with various crystalline structures, thicknesses and TB fractions were investigated to study the roles of the free surface and TB in the phase transition. In the austenitic phase transition, the new phase nucleates mainly at the (112)bcc TB in the thicker films. The (111¯)bcc free surface only attends to the nucleation, when the film is extremely thin. The austenitic transition temperature shows weak dependence on the film thickness in thicker films, while an obvious transition temperature decrease is found in a thinner film. TB fraction has only slight influence on the austenitic temperature. In the martensitic phase transition, both the (1¯10)fcc free surface and (111)fcc TB attribute to the new body-center-cubic (bcc) phase nucleation. The martensitic transition temperature increases with decreased film thickness and TB fraction does not influent the transition temperature. In addition, the transition pathways were analyzed. The austenitic transition obeys the Burgers pathway while both the Kurdjumov–Sachs (K–S) and Nishiyama–Wassermann (N–W) relationship are observed in the martensitic phase transition. This work may help to understand the mechanism of phase transition in the Fe nanoscaled system containing a pre-existing defect.

Molecular Dynamics Simulation of Nanocrystalline Tantalum under Uniaxial Tension

2008 ◽  
Vol 139 ◽  
pp. 83-88 ◽  
Author(s):  
Zhi Liang Pan ◽  
Yu Long Li ◽  
Qiu Ming Wei
Keyword(s):  
Phase Transition ◽  
Molecular Dynamics ◽  
Grain Size ◽  
Phase Transitions ◽  
Strain Rate ◽  
Uniaxial Tension ◽  
Rate Sensitivity ◽  
Dynamics Simulation ◽  
Face Centered Cubic ◽  
Nanocrystalline Iron

Using molecular dynamics (MD) simulation, we have investigated the mechanical properties and the microstructural evolution of nanocrystalline tantalum (NC-Ta, grain size from 3.25 nm to ~13.0 nm) under uniaxial tension. The results show the flow stress at a given offset strain decreases as the grain size is decreased within the grain size regime studied, implying an inverse Hall-Petch effect. A strain rate sensitivity of ~0.14, more than triple that of coarse-grain Ta, is derived from the simulation results. Twinning is regarded to be a secondary deformation mechanism based on the simulations. Similar to nanocrystalline iron, stress-induced phase transitions from body-centered cubic (BCC) to face-centered cubic (FCC) and hexagonal close-packed (HCP) structures take place locally during the deformation process, The maximum fraction of FCC atoms varies linearly with the tensile strength. We can thus conclude that a critical stress exists for the phase transition to occur. It is also observed that the higher the imposed strain rate, the further delayed is the phase transition. Such phase transitions are found to occur only at relatively low simulation temperatures, and are reversible with respect to stress.

INDUCED CHANGES OF THERMOTROPIC PROPERTIES OF PHASE TRANSITIONS BETWEEN SMECTIC A MESOPHASE AND ISOTROPIC LIQUID: EFFECT OF SURFACES

2006 ◽  
Vol 20 (14) ◽  
pp. 821-833 ◽  
Author(s):  
ARIF NESRULLAJEV ◽  
ŞENER OKTIK
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Phase Transition ◽  
Phase Transitions ◽  
Isotropic Liquid ◽  
Smectic A ◽  
Phase Transition Temperatures ◽  
Smectic A Phase ◽  
Induced Changes ◽  
Thermotropic Properties

In this work, the effect of thin films on the thermotropic and thermo-optical properties and peculiarities of the phase transitions between the smectic A and isotropic liquid have been investigated. Peculiarities of the heterophase regions of the straight smectic A-isotropic liquid and reverse isotropic liquid-smectic A phase transitions have been studied. Change of morphologic properties of the heterophase regions, shift of the phase transition temperatures and the change of temperature widths of these heterophase regions under thin film influence have been observed.

The Study on Young's Modulus of Multilayered Cu/Ni Multilayered Nano Thin Films by Molecular Dynamics Simulation

2014 ◽  
Vol 513-517 ◽  
pp. 113-116
Author(s):  
Jen Ching Huang ◽  
Fu Jen Cheng ◽  
Chun Song Yang
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Strain Rate ◽  
Young’S Modulus ◽  
Potential Function ◽  
Dynamics Simulation ◽  
System Temperature ◽  
Simulation Results

The Youngs modulus of multilayered nanothin films is an important property. This paper focused to investigate the Youngs Modulus of Multilayered Ni/Cu Multilayered nanoThin Films under different condition by Molecular Dynamics Simulation. The NVT ensemble and COMPASS potential function were employed in the simulation. The multilayered nanothin film contained the Ni and Cu thin films in sequence. From simulation results, it is found that the Youngs modulus of Cu/Ni multilayered nanothin film is different at different lattice orientations, temperatures and strain rate. After experiments, it can be found that the Youngs modulus of multilayered nanothin film in the plane (100) is highest. As thickness of the thin film and system temperature rises, Youngs modulus of multilayered nanothin film is reduced instead. And, the strain rate increases, the Youngs modulus of Cu/Ni multilayered nanothin film will also increase.

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