a molecular dynamic study on the influence of...
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CMM, Characterizing and modeling of materials – from nano to macro, KaU (1)
10th Tool conference 2016, 4-7 October, 2016, Bratislava Slovakia
A MOLECULAR DYNAMIC STUDY ON THE INFLUENCE OF CARBIDE PARTICLES IN FERRITE ON MATERIAL TRANSFER DURING NANOSCR-
ATCHING OF FERRITIC IRON
Ahmed Tamer AlMotasem, Jens Bergström, Anders Gåård, Pavel Krakhmalev, Thijs
Jan Holleboom
CMM, Characterizing and modeling of materials - from nano to macro, Karlstad University.
11/4/2016
بسم هللا الرحمن الرحيم
CMM, Characterizing and modeling of materials – from nano to macro, KaU (2)
Surface damage related to material transfer and
adhesive wear in sheet metal forming (SMF)
operations is known as galling.
Galling
slider-on-flat-surface(SOFS) tribometer.
P. Karlsson et al. / Wear 319 (2014) 12–18
Overview
Improving anti-galling properties
– Coating with carbides or nitrides films.
– Lubricants
– Introducing carbide or nitride precipitates into
tool
– Material transfer to from sheet to tool matrix as
well as to the hard phases but to a lesser extent
– Lower friction through carbides
worn PM2 tool steel
CMM, Characterizing and modeling of materials – from nano to macro, KaU (3)
http://xqwang.engr.uga.edu/
Multi-scale modelling is a hierarchical process
Multi-scale Modeling
CMM, Characterizing and modeling of materials – from nano to macro, KaU (4)
Galling
Quantum Approach
Adhesive wear
Molecular Dynamics
– Interface structure and energy. – Bond strength. – Work of adhesion.
– Deformation mechanism. – Material pile-up. – Ploughing. – Friction.
Abrasive wear
How can multiscale modeling help in understanding experimental observations?
Atomistic modeling
CMM, Characterizing and modeling of materials – from nano to macro, KaU (5)
Molecular Dynamics Simulation
1
( )2
i i ij ij ij
i j i
E F S R
Second nearest neighbor modified embedded atom method (2NN MEAM)
− Force field is the core of molecular dynamics simulation.
− Parametrization of the potential based on both DFT and experimental results.
Pair interaction Embedding
energy
− Predict correctly surface energy of low index surfaces (110)<(100)<(111)
− Parametrization of the potential based on both DFT and experimental results.
− Can model stable structure of carbide.
CMM, Characterizing and modeling of materials – from nano to macro, KaU (6)
- Workpiece: (110) surface, bcc iron. - Tool: bcc iron+Fe3C - periodic boundary condition in lateral Directions, 571000 atoms
Two stage simulation I- Nanoindentation - Velocity 10 m/s - Indentation depth 6 Å
II- Nanoscratching - Velocity 50 m/s - Scratch distance 100Å
Molecular Dynamics Simulation setup
Tool
Dimensions (Å) 40.9×42.5× 40.9
T1 0% cementite
T2 3.6% cementite
T3 24% cementite
CMM, Characterizing and modeling of materials – from nano to macro, KaU (7)
– The total dislocation length is reduced when carbide is added into tool.
– Formation of nanovoids as a result of dislocations annihilation.
Plastic deformation during nanoscratching
CMM, Characterizing and modeling of materials – from nano to macro, KaU (8)
− Plastic deformation dominated by nucleating and interacting
dislocations.
− Two kinds of dislocations were identified using DXA algorithm.
− The plastic zone size is lower when increasing cementite
precipitate radius.
Plastic deformation during nanoindentation
CMM, Characterizing and modeling of materials – from nano to macro, KaU (9)
Frictional and Normal forces
– Average value of frictional forces decrease with increasing carbide content.
– Average value of normal forces increase with increasing carbide content.
CMM, Characterizing and modeling of materials – from nano to macro, KaU (10)
fF S P
Qualitative explanation of reduction of frictional forces
According to Bowden and Tabor (BT) friction model, the frictional force can be written as
Shearing Plowing
F.P. Bowden, A.J.W. Moore, D. Tabor, J. Appl. Phys. 14 (1943) 80–91
The observed decrease in average frictional force with increasing carbide contents may be
ascribed to the decrease of the shear due to amorphousity and the decrease of wear
volume.
Tool Ff
(nN)
Fn
(nN) µ
Ldis
(Å)
Wsp
(nm2/µN)
T1 355.4 112.1 0.44 481.5 31.07
T2 275.6 165.7 0.32 230.21 29.51
T3 245.3 218.7 0.23 196.13 28.6
totalsp
n
VW
F L
CMM, Characterizing and modeling of materials – from nano to macro, KaU (11)
Pileup characteristic
– Frontal and lateral pileup at the end of scratching. – The work done by the tool is
CMM, Characterizing and modeling of materials – from nano to macro, KaU (12)
2 2 2 2 2 2
von mises
( ) ( ) ( ) 6( )
2
xx yy yy zz zz xx xy yz zx
Qualitative explanation of increase of normal forces with carbide contents
The increase of the normal force with carbide contents can be attributed to the relieve of stress
due to dislocation nucleation In the workpiece material.
AlMotasem et al., Wear, submitted.
CMM, Characterizing and modeling of materials – from nano to macro, KaU (13)
Commensurateness of tool/workpiece interface
3 3TH b 3 3TH b
3 3TH b
f
cAsc
FH
Scratch hardness is defined as the resistance of the
material to scratch
: Shear modulus
: Burgers vector
: constant between 0-0.5
b
The average value of the scratch hardness of the
workpiece material decreases with increasing
carbide content in the tool.
According to Taylor hardening model, which relates the hardness to the dislocation density by:
The Hardness of Metals. Oxford, Clarendon Press, 1951, 1970.
CMM, Characterizing and modeling of materials – from nano to macro, KaU (14)
Adhesive force between Fe/Fe and Fe3C/Fe counterfaces
CMM, Characterizing and modeling of materials – from nano to macro, KaU (15)
Adhesive force between Fe/Fe and Fe3C/Fe counterfaces
– The adhesive force between Fe/Fe3C is lower than that of Fe/Fe.
MD snapshot showing adhered atoms between
Fe/Fe and Fe3C/Fe at the end of retraction process.
Force versus distance of counter surfaces Fe/Fe
(red) and Fe3C/Fe (black).
CMM, Characterizing and modeling of materials – from nano to macro, KaU (16)
– Adhesive force between Fe/Fe counter surfaces,
initially increases then decreases.
– Adhesive force between Fe3C/Fe decreases with
temperature.
– Inset, AFM result of bcc iron. MD results higher than
AFM results may be due to formation of oxide layers.
Adhesive force versus temperature
AFM results of bcc iron, Anders Gåård, Ph.D thesis
ad A B ABW
Temperature
(K)
Work of adhesion (Jm-2)
Fe/Fe Fe3C/Fe
300 11.38 10.12
400 12.42 9.83
500 12.31 9.10
600 11.08 9.00
700 10.57 7.77
CMM, Characterizing and modeling of materials – from nano to macro, KaU (17)
Commensurateness of tool/workpiece interface
– Commensurateness is observed between tool/workpiece interface.
– The more commensurateness, the higher adhesion.
AlMotasem et al, Tribology International, 103 (2016) 113-120
The values of the adhesive force corresponding to each rotation angle is calculated and
the results of adhesive force exhibit a U-shaped curve with a minimum at θ=30.
.
CMM, Characterizing and modeling of materials – from nano to macro, KaU (18)
Conclusion
– Both the dislocations length and density were greatly affected by the tool microstructure
– the wear volume of the workpiece material was reduced by about 33% with increasing carbide content in the tool
– temperature induced crystal-amorphous phase transformation has been confirmed by the radial distribution function analysis
– In general, Fe/Fe has a higher adhesion force and work of adhesion compared to the case of Fe3C/Fe counterfaces
– It is observed that while both the Fad and Wad initially slightly increase up to 500 (K) then decreases for Fe/Fe, they always decrease in the case of Fe3C/Fe counterfaces.
– The present results explain the important role of the lattice match/mismatch on material transfer, and thus it can help to design a material with improved wear resistance by optimizing grains orientation.
CMM, Characterizing and modeling of materials – from nano to macro, KaU (19)
Thank you for your attention