-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
1
Wear Mechanisms1 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Wear and Wear Mechanisms
Wear Mechanisms2 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Wear and Wear Mechanisms
There is no simple relationship between wear and any other
materialsproperty
Thus we always have to take into account that wearis not a
materials property like e.g. strenghtis a property of a specific
tribosystemhas to be evaluated for every tribosystemcannot be
generalized in detail
On the basis of known mechanisms oncan understand the
charactreistics of a tribosystem andcan take care of well-aimed
counter measures
without the knowledge of the mechanisms you can follow
trial-and-error
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
2
Wear Mechanisms3 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Wear and Wear Mechanisms
There is no simple relationship between wear and any other
materialsproperty
In order to underastand the mechanism dependant counter measures
on can follow the very (!) simple model of Archard (1959)
Archards equation (not law!!) is
W
Ns H
FksWW ==
The wear rate W related to the wear path s is proportional to
the normal load FN and the hardness of the worn surface HW and a
factor k.
k describes the probability to generate a wear particle during
the path s and contains all constants and variables of a
tribosystem.
Wear Mechanisms4 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Wear MechanismsAdhesion
Surface Fatigue
Abrasion
Tribochemical Reactions
k depends on theacting wearmechanisms and can be describedonly
qualitatively!
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
3
Wear Mechanisms5 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Wear Mechanisms
Verschleikoeffizient k
k might vary between more thannine orders of magnitudedepending
on the acting wearmechanism (and submechanisms)
wear coefficient k
Wear Mechanisms6 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Mechanically Dominated Wear Mechanisms
Surface Fatigue
Abrasion
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
4
Wear Mechanisms7 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Surface Fatigue
under rolling wear
under sliding wear
Surface fatigue is brought about by crack initiation and
propagation, whichmight take place at the surface or in a certain
distance below it. Thatdepends on the contact situation and the
microstructure of the contactingmaterials.
Wear Mechanisms8 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Surface Fatigue (rolling wear)
Appearances of surfacefatigue on a wheel of a harbour crane made
out of perlitic cast ironGJS-1000 (AISI A538)
Taper section of the worn surface
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
5
Wear Mechanisms9 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Surface Fatigue (sliding wear)Appearances of surfacefatigue on
the cylinderwall made out of hardened and temperedsteel 42CrMo4
(AISI4140) under sliding wear of an hydraulic pump.
The counterbody was a chromatized piston ring
Throttle-disc pump
Wear Mechanisms10 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Surface Fatigue (cavitation)
Appearances of surface fatigueunder cavitation on the
cylinderwall made out of hardened and tempered steel 42CrMo4
(AISI4140) of an hydraulicpump.
Notice: There is no counterbody under cavitation
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
6
Wear Mechanisms11 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Surface Fatigue (rolling wear)
Appearances of surface fatigue underrolling wear on the cage of
a rollerbearing out of hardened and tempered steel 100Cr6
(AISI52100).
Source: VDI5932-5, VDI, Duesseldorf, Germany
Wear Mechanisms12 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Surface Fatigue (3-body abrasive wear)
Appearances of surface fatigueunder 3-body abrasive wear
Groove (abrasion) indentation (surface fatigue)v
de a o
v
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
7
Wear Mechanisms13 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Surface FatigueIf we assume that surface fatigue is similar to
fatigue even though the stress filed is much more complictated we
can use the general rules of fatigue e.g. Mason&Coffin(1959)
adapted to contact mechanics:
mf
fN
= Nf is the number of cycles to fracture, f the
equivalent (plastic) deformation to fracture underone loading
cycle, the equivalent deformation per loading cycle, and m an
exponent, which is 2 to 3 for metals under a plastic contact
*m
v
vffN
= Nf is the number of cycles to fracture, vf theequivalent
stress to fracture under one loading
cycle, v the equivalent stress per loading cycle, and m* an
exponent, which is 1.2 to 8 for metals underan elastic contact
Wear Mechanisms14 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Surface FatigueThus the probability for the generation a a wear
particle k becomes thereciprocal of Nf:
m
fSFplSF Ck
=
.
*
.
m
vf
vSFelSF Ck
=
giving for an elastic contact situation(after run-in) W
Nm
vf
vSFsSF H
FCW*
.
=
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
8
Wear Mechanisms15 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Surface FatigueCountermeasures
W
Nm
vf
vSFsSF H
FCW*
.
=
In order to gain a small wear rate under surface fatigue with
CSF=const. and m*=const. In a given tribosystem we should
1) decrease v (and FN) and 2) increase vf as well as HW
1) decrease by lubrication, introduce compressive residual
stresses, avoid internal (non metallic inclusions, hard phases) and
external(roughness, pores) notches
2) increase endurance limit by strenght and purity, ductility
(f), coldworking capability (HW)
Notice: v depends on FN and
Wear Mechanisms16 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Mechanically Dominated Wear Mechanisms
Surface Fatigue
Abrasion
from kennecott02 (Copyright 2000 by Daniel Ter-Nedden)
Kennecott, UT
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
9
Wear Mechanisms17 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
AbrasionAbrasion is brough about by an hard or sharp particle
(e.g. mineral particle) or proturberance(e.g. surface asperity)
imposedon and moving on a (softer) surface.
Abrasion has foursubmechanisms, which dependon the structure of
thetribosystem and the properties of the materials in contact.
Wear Mechanisms18 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion (under sliding wear)
Appearance of abrasion under sliding wear of a WC cemented Co
hardmetal shaft of a measuring device, which slides against a Ruby
(corundum, Al2O3) bearing under water cooling
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
10
Wear Mechanisms19 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion (under solid particle erosion)
Appearance of abrasionunder solid particle erosionof shovels of
a Peltonturbine
Wear Mechanisms20 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion (under 3-body rolling abrasive wear)
Appearance of abrasion underrolling abrasive wearof a cement
millroller
microcutting microcracking
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
11
Wear Mechanisms21 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion (under sliding wear)
Appearance of abrasion under slidingwear of a cup of a retrieved
McKee-Farrar metal-on-metal prosthesis
Wear Mechanisms22 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion
Microploughinga certain fraction of thegrooved material is just
shifted to the edges of the rim. Thus, it is notlost!
MicrocuttingThe groovedmaterial generatesa chip, which
islost.
The worn amount of material is smallerthan the volume of
thegroove!
The worn amount of material is equal to thevolume of the
groove!
MicrocrackingThe groovedmaterial generatescracks underneathand
beneath of the groove. The worn amount of material is bigger
thanthe volume of thegroove!
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
12
Wear Mechanisms23 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion
MicrofatigueThe material beneaththe grooves duringmicroploughing
ormicrocutting is fatiguedby multiple passes of the indenter
During a single contact the deformationbeneath a groove depends
on thedeformation of the equivalent deformation at the first pass v
and the work hardeningcapability HW/H according to
3HH
v
W
e=
In analogy to the surface fatigue model onecan write that the
number of cycles to generate a wear particle is
m
v
HH
vff
W
eN
=
321
Wear Mechanisms24 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion1/WAB.s vs. H
precipitationhardening
hardening by straininduced phasetransformationduring wear
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
13
Wear Mechanisms25 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion
The ratio between the grooved volume and that which is shifted
to theedges of the rim can be described by the fab-value, which
depends on thelocal equivalent surface deformation during
scratching v and theequivalent deformation to fracture vf for
ductile materials under e.g. rolling or drawing. In addition the
work hardening capability has to beincorporated by Hw/H.
vf
v
WHH
ab efln2
3
1
=
fab - per defintion - lies between 0 forv
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
14
Wear Mechanisms27 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion
Thus the wear by abrasion under microploughing and microcutting
under a multiple contact resulting in microfatigue can be written
as
sfatiguescuttingploughingsAB WWW ... += +
( )
+
+=
2tan1
tan101
5
21
22
.3
RHF
e
NffW
defW
N
m
HH
vf
vababsAB
W
where N Nf, R = tip radius of the indenter and 2 the apex angle
of the indenter
Wear Mechanisms28 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
AbrasionBecause of the action and interaction of these
submechanisms no simple relation exists between the hardness of the
materials and their wearresistance under abrasion!
In order to increase the wear resistance one should increasethe
hardness H, the hardness ratio (HW/H) and the ductility expressed
by vf.
Notice: By increasing H usually vf decreases. Thus there is an
optimumcombination of both for every single tribosystem.
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
15
Wear Mechanisms29 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion (by a single hard indenter) = 85, 2 = 115, v = 1.8 m/s,
FN = 1 N
def=0.17 def=0.09NiCr20AlTi CoCr27Mo3C0.4HW/H small HW/H large +
second hard phase
Wear Mechanisms30 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion (influence of the tribosystem e.g. hardness of abrasive
particle)
The wear rate under abrasionstrongly depends on thehardness
ratio between thematerials of body and indenter.
There is a steep increase in the wear rate, if the hardnessratio
becomes bigger than 0.7.
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
16
Wear Mechanisms31 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion (influence of the tribosystem e.g. shape of the
abrasive particle)
A blunt or soft indenteror a shallow attackingangle produces
lesswear, becausemicroploughing isprevailing;
with a sharp indentermicrocutting does and the wear rate
increases.
Thus the geometry of the indenter is as important as the
ductilityof the grooved materials!
Microplouging
Microcutting
Wear Mechanisms32 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion
if pc > pcrit
H, HW
vf , KIc
1/Wab.s vs. HW
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
17
Wear Mechanisms33 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion
pcrit is a function of the size and shape of the abrasive
particle and thefracture toughness Kc of the material
Notice: The higher the hardness the lower the fracture
toughness!
e.g. for ceramics
tan2sintan
6.2
222
HDKdp
ab
IIcvoidscrit
=
Dvoids = distamve between voidsKIIc = fracture toughness under
shear stresses (mode II cracks)H = hardness (Notice: HW=H for
ceramics!)Dab = average size of abrasive particles
Wear Mechanisms34 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion
Microcracking takes place if the local contact pressure pc is
higher thanthat for crack initiation pcrit. From these on can
derive the probability of microcracking by
crit
cpp
e
= 1
pcrit depends on whether1) there are brittle second phases
within the
groove2) There are brittle second phases beneath the
groove3) cracks are generated in and propagate through
the matrix material4) cracks are generated at and propagate
along
grain boundaries and5) cracks propagate by combining existing
cracks
or voids within the microstructure
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
18
Wear Mechanisms35 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Abrasion
Wear Mechanisms36 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
AbrasionThe general wear rate under abrasion can then be
expressed in a generalform by
scrackingsfatiguescuttingploughingsAB WWWW .... ++= +( )
++= 222
21. 1c
defWnnabvoids
fabab
W
nsAB
K
HpDf
NNff
HpW
1,2 depend on the shape of abrasive particlesfvoids = volume
fraction of significant internal notchesn = 1 for cracks and 3 for
grain boundaries
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
19
Wear Mechanisms37 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
AbrasionCountermeasures
In order to gain a small wear rate under abrasion with 1,2, Dab
= const. In a given tribosystem we should
1) decrease friction def, pN2) increase H, HW, HW/H, vf,
KIc,
1) decrease and p, pN by small particles or lower FN2) increase
hardness H by martensitic hardening, HW/H by precipitationhardening
or choosing materials with a low stacking fault energy, or
makebenefit of strain induced phase transformation, embedd second
hardphases (volume fraction, size, distribution) if matrix is
strong enough to support them, introduce compressive residual
stresses3) use 2) without loosing too much of vf and KIc
Wear Mechanisms38 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Chemically-Mechanically Dominated Wear Mechanisms
Adhesion
Tribochemical Reactions
pictures from www.en.wikipedia.org
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
20
Wear Mechanisms39 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Adhesion
Adhesion is brought about by (friction welded) microjoints.
Asperities of body and counterbody are plastically deformed with
subsequentdestruction of any intermediate layer. The separation of
this joint takesplace within the non-cold worked reagion underneath
the contact area. Thus there is materials transfer from body to
counterbody and vice-versa.
microjoint
separation
Wear Mechanisms40 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Adhesion (under recipricating sliding wear)Appearances of
adhesion followed by abrasion under reciprocating slidingwear of an
overheated (and, therefore, unlubricated)
cylinder/pistoncontact.
http://knowhow.windstar-club.de/index.php/Kolbenfresser_(BJ.1999-2000)
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
21
Wear Mechanisms41 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Adhesion (under sliding wear)Appearances of adhesion under
self-mating sliding wear of a martensitichardfacing alloy
(X45CrMnMo6-2, H13 warm-work tool steel).
materials transfer
Pit
grooveDue to the factthat aftermaterialstransfer
thesurfacesbecomerougher and harder, adhesion isoftenaccompaniedby
abrasion.
Wear Mechanisms42 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Adhesion (under sliding wear) materials transfer
pit
groove
Appearances of adhesion on thecylinder wall madeout of hardened
and tempered steel42CrMo4 (AISI4140) undersliding wear of an
hydraulic pump.
The counterbodywas a chromatizedpiston ring
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
22
Wear Mechanisms43 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Adhesion
W
Ns H
FksWW ==
Adhesion can only be described roughly and cannot be
quantizised; Archards general wear equation is taken
While k is used similar to the k forfriction
fracdefadAD kkkk ++=it contains an adhesive term (for the
tendency of materials to adhere to each other), an deformation term
(because plastic deformation increasesthe real area of contact in
which adhesion takes place) and a fracture term(because for the
generation of a wear particle crack initiation and propagation has
to take place)
Notice: kAD has a dimension differing from that of friction,
because herealso material is dissipated
Wear Mechanisms44 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Adhesion
2
cot21
1
aH
kad
ad kad can be described similar to ad
Thus the tendency to adhere depends on the surface energy ad and
on thechemical similarity of surfaces
2,121 +=adif 1 and 2 are dissimilar the interaction term 1,2
might become very large. In addition the solubility within each
other play an important role, as well as the lattice orientation
(density of atoms)
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
23
Wear Mechanisms45 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Adhesionkad 2,121 +=ad
Nat %nmmJ/mkJ/g atom
1400insoluble0.349500197Pb
500
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
24
Wear Mechanisms47 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
AdhesionCounter measures
fracdefadAD kkkk ++=
The three terms of adhesion cannot beseparated
W
Ns H
FksWW ==
1) avoid direct metal-metal contact between body and
counterbody2) decrease , ad3) Increase H, HW, HW/H
for 1) lubricate the contactfor 2) decrease FN, use dissimilar
materials (e.g. steel-brass (ad), -polymer
(water adsorbtion on surface (, ad)), -ceramic (high bonding
energy!) (ad), benefit from inhomogenous microstructure
ceramic+metal (perlite) instead of just metal (martensite) or Al-Si
casting (Si+AlSi solid solution)
for 3) use ceramics H, HW for a small AC
Wear Mechanisms48 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Reibungszahl f0,4 0,45 0,5 0,55 0,6 0,65
0,01
0,1
1
10MMMM+fHPMM+fHP+gHP
Adhesion under unlubricated self-mating sliding wear
slid
ing
wea
rra
te W
x10
-6
coefficient of friction
adhesion by directmetal-metalcontact
mechanical interlocking byprotruding hard-phases(ceramic-ceramic
contact)
pn=0.83 MPav=0.028 m/sRT, air
kad+kdef
Kdef+kfrac
metal matrix
metal matrix + eutectic hard phases
metal matrix + eutectic + primary hard phases
A1010 H13
NiCr20AlTi
D12 hard+temp.
D12 soft
Stellite21
FeCr5B5
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
25
Wear Mechanisms49 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Chemically-Mechanically Dominated Wear Mechanisms
Adhesion
Tribochemical Reactions
Wear Mechanisms50 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Tribochemical Reactions
reaction layer
Tribochemical Reactions are brought about by the
tribologicallyinduced chemical reaction of the materials of body an
counter body withthe interfacial medium and the environment.
Notice: Tribochemical rections bring about reaction products
which arenon metallic (e.g. oxide) and, therefore, hinder
adhesion!
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
26
Wear Mechanisms51 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Tribochemical Reactions (under fretting)Appearance of
Tribochemical Reactions (films, layers, scales)
Brownish or reddish layer within contact area of a bar and a
plate generated by small strokesbetween press-fitted parts
(fretting) caused bymachine vibrationfrom
http://www.gitz-online.de/EWIS-GITZ-Workshop-2003.pdf
Wear Mechanisms52 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Tribochemical Reactions (under sliding wear)Appearance of
Tribochemical Reactions (films, layers, scales)
Denatured proteins on thesurface of a metal-on-metal hip ball,
which has been run againsta pin in bovine serum
torque sensor
ball
pin
Notice: There are also appeaeances of abrasion (grooves) and
surfacefatigue (indentations)!
FN=750 NTE=37Cv~0.0293m/s
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
27
Wear Mechanisms53 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Tribochemical ReactionsTribochemical Reactions are very complex
and less understoood. They canbe seen as a combination of
- Tribosorption- Tribodiffusion (accelerated by lattice defects
of deformed surface
volume or any other mechanism) and- Tribochemical Reaction e.g.
Tribooxidation
The local energy must be very high, so that chemical reactions
take place, which normally wouldnt. E.g. oxidation of Cu in CO2
atmosphere accordingto
COCuCOCu ++ 22 24 has a free energy of G=+102 kJ/molCO2. Thus it
would never take place. Butunder tribological circumstances in a
ball mill with Cu chips it has been observed.
Wear Mechanisms54 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Wear and Wear Mechanisms COCuCOCu ++ 22 24Under thermodynamic
equilibrium one can write
)(2OMOMox yGxGGG yx +=
In addition we know that Gox depends on the partial pressure of
O2 acc. to
yO
oxp
G2
1ln
This would require a pressure of 5.7x1035 bar ( 83x1035
psi)!!
Thus it is more likely that GM becomes extremely large by
plastic deformation!
or anything else is going on
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
28
Wear Mechanisms55 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Tribochemical Reactions under mild sliding wear ( < 0.6)For
tribooxidation Quinn(1983) has described the wear rate as function
of physical, chemical and mechanical properties of the reaction
products. He states that wear is brought about by spalling off an
oxide layer, which has reached its critical thickness dc
222.oxox
RTQ
pC
csTCR
g
eAvA
ddW
C
p
=
d = surface separationdc = critical oxide layer thicknessAp =
Arrhenuis constant fortribooxidationQp = activation enerty for
oxidationgox = weight content of O in oxideox = density of
oxide
Wear Mechanisms56 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Tribochemical Reactions under mild sliding wear ( < 0.6)
22.oxox
RTQ
pC
csTCR
g
eAvA
ddW
C
p
=
This means that WTCR.s becomes smallfor a slow growth rate of
the oxide, described by the Arrhenius part (smallAp and TC, high
Qp)
Notice: For a const. Qp under staticand tribooxidation Ap under
wearbecomes 11 orders of magnitudebigger compared to static
oxidation!
But because of Ta and Tf the heat conductivity of the oxides as
well as the coefficient of thermal expansion of oxides and
substrate play an important role as well.
-
Hhere Werkstofftechnik: Tribologie Wear Mechanisms
29
Wear Mechanisms57 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Tribochemical ReactionsCounter measures
Because tribochemical reactions cause less wear and hinder
adhesion onewould not really look for any counter measures unless
the electricconductivity is of importance or you are in the field
of MEMS or NEMS.
In that case useoxidation resistantalloys (noble metals) or
those with a slowgrowth rate of oxides(ceramics). In addition
vacuum oran inert gas atmosphere mighthelp as well.
e.g. Polysilicon MEMS fatigue life test setup. Crack initiation
within the 10 nm thin oxide reaction layer inside the notch might
limit the fatigue life (from R.O.Ritchie, UCB)
Wear Mechanisms58 www.uni-due.de/wt
Universitt Duisburg-EssenLotharstr 1, 47057 Duisburg,
Germany
WerkstofftechnikMaterials Science & Engineering
Tribochemical Reactions
Wear path in m
Ni (200 HV) < NiO (400 HV)
Al (200 HV)