Atomistic insights into anti-wear mechanisms and protective tribofilm formation in polytetrafluoroethylene composites

2021 ◽  
pp. 1-31
Author(s):  
Wei Sun ◽  
Jiaxin Ye ◽  
Xiaojun Liu ◽  
Kun Liu
Keyword(s):  
Wear Mechanisms ◽  
Density Functional ◽  
Wear Behavior ◽  
Environmental Water ◽  
Transfer Film ◽  
Polar Polymers ◽  
Macro Scale ◽  
The Matrix ◽  
Dynamics Simulations ◽  
Ptfe Composites

Abstract Polytetrafluoroethylene (PTFE) has a low friction coefficient but poor wear resistance (k ~ 10−3 mm3/Nm) against various surfaces. Mechanical modeling suggests that the enhanced anti-wear performance of PTFE composites (k ~ 10−5 mm3/Nm) relies on load support by filler in the matrix. Recent studies found that tribochemical polarization of PTFE polymers triggered the formation of highly protective transfer film, thus resulting in an exceptionally low wear (k ~ 10−7 mm3/Nm) in certain composites. However, atomistic interaction was believed to play an important role in the known anti-wear mechanisms, which has yet to be fully described. Here, environmental and computational experiments allowed detailed mechanistic studies for representative PTFE composites, including metal-, ceramic-, carbon-, and polymer-filled composites. Experimental results found that the protective and polarized transfer film formed only in environmental water/oxygen, which could also reduce the composite wear by 10-fold or more. Density-functional-theory (DFT) calculations revealed that the electrophilic atom at solid surface tends to defluorinate PTFE molecule, which enables the tribochemical products of polarized PTFE accumulated near the sliding surfaces. Molecular dynamics simulations suggested that the strengthening of nonbonding interactions resulted from polar polymers improved polymer composites' adhesion and cohesion strengths against steel counterface, which was responsible for the achievement of macro-scale ultralow wear in PTFE composites. The relation between the atomistic interactions and the macroscopic wear behavior of composites was systematically discussed.

Physico-mechanical, thermal, and tribological studies of polytetrafluoroethylene-filled polyoxymethylene/silicone composites

2020 ◽  
pp. 089270572092511
Author(s):  
MR Shankare Gowda ◽  
AB Hemavathi ◽  
S Srinivas ◽  
G Santhosh ◽  
Hatna Siddaramaiah
Keyword(s):  
Impact Strength ◽  
Friction And Wear ◽  
Room Temperature ◽  
Wear Behavior ◽  
Transfer Film ◽  
Negative Effects ◽  
Wear Performance ◽  
Mating Surface ◽  
Injection Molded ◽  
Ptfe Composites

Polyoxymethylene (POM)-based composites with polytetrafluoroethylene (PTFE) filler and silicone gum have been prepared by melt extrusion to enhance the wear resistance and friction lubrication of POM without compromising the other desired properties such as modulus, toughness/impact strength, notch insensitivity, and thermal stability. The compounded material was injection molded to prepare test specimens, and their physico-mechanical properties were evaluated. In addition, thermal and tribological characteristics of the composites were also studied. The addition of silicone into POM/PTFE composites could enhance the formation of stable transfer film on the mating surface during sliding contact, thus improving the friction and wear performance, as silicone forms synergistic mixture with PTFE. It was found that the tensile, flexural, and notched impact strength remained almost constant for all the formulations. The use of PTFE improved the unnotched impact strength (from 35.5 to 42.9 kJ m−2). The toughening effect can be attributed to the dissipation of impact energy through soft PTFE and ductile silicone phase. Differential scanning calorimeter results revealed that there are no negative effects on POM crystallinity due to the presence of PTFE and silicone. The wear behavior of composites has been investigated under dry sliding conditions at different normal loads and sliding velocities at room temperature. The POM/PTFE/silicone (90/8/2 wt/wt%) formulation exhibits better wear-resistant behavior in the present study.

Effect of High Temperature on Wear Behavior of Stir Cast Aluminium/Boron Carbide Composites

2020 ◽  
Vol 22 (4) ◽  
pp. 1031-1046
Author(s):  
X. Canute ◽  
M. C. Majumder
Keyword(s):  
High Temperature ◽  
Wear Rate ◽  
Boron Carbide ◽  
Wear Behavior ◽  
Base Alloy ◽  
Weight Fraction ◽  
Sliding Velocity ◽  
Wear Properties ◽  
High Temperature Wear ◽  
The Matrix

AbstractThe need for development of high temperature wear resistant composite materials with superior mechanical properties and tribological properties is increasing significantly. The high temperature wear properties of aluminium boron carbide composites was evaluated in this investigation. The effect of load, sliding velocity, temperature and reinforcement percentage on wear rate was determined by the pin heating method using pin heating arrangement. The size and structure of base alloy particles change considerably with an increase of boron carbide particles. The wettability and interface bonding between the matrix and reinforcement enhanced by the addition of potassium flurotitanate. ANOVA technique was used to study the effect of input parameters on wear rate. The investigation reveals that the load had higher significance than sliding velocity, temperature and weight fraction. The pin surface was studied with a high-resolution scanning electron microscope. Regression analysis revealed an extensive association between control parameters and response. The developed composites can be used in the production of automobile parts requiring high wear, frictional and thermal resistance.

A New Phase of the Na+ Ion Conductor Na3PS4

2019 ◽  
Author(s):  
Theodosios Famprikis ◽  
James Dawson ◽  
François Fauth ◽  
Emmanuelle Suard ◽  
Benoit Fleutot ◽  
...  
Keyword(s):  
Solid Electrolytes ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Orthorhombic Crystal ◽  
Orthorhombic Crystal Structure ◽  
Ion Conductor ◽  
Solid State Batteries ◽  
Density Analysis ◽  
Two Phases ◽  
Dynamics Simulations

<div> <p>Solid electrolytes are crucial for next‑generation solid‑state batteries and Na<sub>3</sub>PS<sub>4</sub> is one of the most promising Na<sup>+</sup> conductors for such applications. At present, two phases of Na<sub>3</sub>PS<sub>4</sub> have been identified and it had been thought to melt above 500 °C. In contrast, we show that it remains solid above this temperature and transforms into a third polymorph, γ, exhibiting superionic behavior. We propose an orthorhombic crystal structure for γ‑Na<sub>3</sub>PS<sub>4</sub> based on scattering density analysis of diffraction data and density functional theory calculations. We show that the Na<sup>+</sup> superionic behavior is associated with rotational motion of the thiophosphate polyanions pointing to a rotor phase, based on <i>ab initio</i> molecular dynamics simulations and supported by high‑temperature synchrotron and neutron diffraction, thermal analysis and impedance spectroscopy. These findings are of importance for the development of new polyanion‑based solid electrolytes.</p> </div>

Graphene adlayer growth between nonepitaxial graphene and Ni(111) substrate: a promising theoretical scheme

2020 ◽  
Author(s):  
Lijuan Meng ◽  
Jinlian Lu ◽  
Yujie Bai ◽  
Lili Liu ◽  
Tang Jingyi ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Density Functional Theory ◽  
Chemical Vapor Deposition ◽  
Molecular Dynamics Simulations ◽  
Vapor Deposition ◽  
Density Functional ◽  
Chemical Vapor ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Dynamics Simulations

Understanding the fundamentals of chemical vapor deposition bilayer graphene growth is crucial for its synthesis. By employing density functional theory calculations and classical molecular dynamics simulations, we have investigated the...

Impact of vibronic coupling effects on light-driven charge transfer in pyrene-functionalized middle and large-sized Metalloid Gold Nanoclusters from Ehrenfest dynamics.

2021 ◽  
Author(s):  
Adrian Dominguez-Castro ◽  
Thomas Frauenheim
Keyword(s):  
Molecular Dynamics ◽  
Charge Transfer ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Gold Nanoclusters ◽  
Tight Binding ◽  
Time Dependent ◽  
Effective Strategy ◽  
Dynamics Simulations ◽  
Dependent Density

Theoretical calculations are an effective strategy to comple- ment and understand experimental results in atomistic detail. Ehrenfest molecular dynamics simulations based on the real-time time-dependent density functional tight-binding (RT-TDDFTB) approach...

scholarly journals H2 Transformations on Graphene Supported Palladium Cluster: DFT-MD Simulations and NEB Calculations

Catalysts ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1306
Author(s):  
Francesco Ferrante ◽  
Antonio Prestianni ◽  
Marco Bertini ◽  
Dario Duca
Keyword(s):  
Atomic Hydrogen ◽  
Density Functional ◽  
Hydrogen Molecule ◽  
Md Simulations ◽  
Vacant Site ◽  
Functional Theory ◽  
H2 Adsorption ◽  
Palladium Cluster ◽  
Supported Palladium ◽  
Dynamics Simulations

Molecular dynamics simulations based on density functional theory were employed to investigate the fate of a hydrogen molecule shot with different kinetic energy toward a hydrogenated palladium cluster anchored on the vacant site of a defective graphene sheet. Hits resulting in H2 adsorption occur until the cluster is fully saturated. The influence of H content over Pd with respect to atomic hydrogen spillover onto graphene was investigated. Calculated energy barriers of ca. 1.6 eV for H-spillover suggest that the investigated Pd/graphene system is a good candidate for hydrogen storage.

Cluster, Surface and Bulk Properties of ZnCd Binary Alloys: Molecular-Dynamics Simulations

2005 ◽  
Vol 502 ◽  
pp. 51-56 ◽  
Author(s):  
Sakir Erkoc
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Density Functional ◽  
Structural Features ◽  
Bulk Materials ◽  
Bulk Properties ◽  
Atom Clusters ◽  
Dynamics Simulations ◽  
Mixed Clusters ◽  
Stable Structures

The structural and electronic properties of isolated neutral ZnmCdn clusters for m+n £ 3 have been investigated by performing density functional theory calculations at B3LYP level. The optimum geometries, vibrational frequencies, electronic structures, and the possible dissosiation channels of the clusters considered have been obtained. An empirical many-body potential energy function (PEF), which comprices two- and three-body atomic interactions, has been developed to investigate the structural features and energetics of ZnmCdn (m+n=3,4) microclusters. The most stable structures were found to be triangular for the three-atom clusters and tetrahedral for the four-atom clusters. On the other hand, the structural features and energetics of Znn-mCdm (n=7,8) microclusters, and Zn50, Cd50, Zn25Cd25, Zn12Cd38, and Zn38Cd12 nanoparticles have been investigated by performing molecular-dynamics computer simulations using the developed PEF. The most stable structures were found to be compact and three-dimensional for all elemental and mixed clusters. An interesting structural feature of the mixed clusters is that Zn and Cd atoms do not mix in mixed clusters, they come together almost without mixing. Surface and bulk properties of Zn, Cd, and ZnCd systems have been investigated too by performing molecular-dynamics simulations using the developed PEF. Surface reconstruction and multilayer relaxation on clean surfaces, adatom on surface, substitutional atom on surface and bulk materials, and vacancy on surface and bulk materials have been studied extensively.

Density-functional-based molecular-dynamics simulations of molten salts

2005 ◽  
Vol 123 (13) ◽  
pp. 134510 ◽  
Author(s):  
Sandrine Hazebroucq ◽  
Gérard S. Picard ◽  
Carlo Adamo ◽  
Thomas Heine ◽  
Sibylle Gemming ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Molten Salts ◽  
Density Functional ◽  
Dynamics Simulations

A Review of Clearance Control Wear Mechanisms for Low Temperature Aluminium Silicon Alloys

1998 ◽  
Author(s):  
F. Ghasripoor ◽  
R.K. Schmid ◽  
M.R. Dorfman ◽  
L. Russo
Keyword(s):  
Wear Mechanisms ◽  
Gas Turbines ◽  
Hexagonal Boron Nitride ◽  
Silicon Alloys ◽  
The Matrix ◽  
Abradable Coatings ◽  
Silicon Based ◽  
Wear Maps ◽  
Clearance Control ◽  
Sprayed Coatings

Abstract Aluminium silicon alloys have shown favourable properties when used as the matrix for abradable coatings in low pressure compressors of gas turbines [1 and 2]. This paper aims to describe the wear mechanisms found in aluminium silicon based abradables. To this end three thermally sprayed coatings are investigated. Aluminium silicon polyester, aluminium silicon-graphite and the most recently developed, aluminium silicon-hexagonal boron nitride (hBN) examined here are amongst a few of these materials. To be able to design materials to functi?n in as wide a parameter range as possible, a test ng simulating engine mechanisms is required. Tests were conducted using titanium blades at velocities ranging from 250 - 450 m/s, temperatures of ambient to 450°C and controlled incursion rate of 5, 50 and 500 µm/s. The data obtained from these tests is best interpreted in the form of wear maps which characterise the seal performance and therefore are of use to engine and material designers.

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