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