Tribodays 2013
Luleå University of Technology
26th -27th September
High temperature wear mechanism maps
Sinuhe Hernandez
1
Supervisors:
Braham Prakash
Jens Hardell
Tribology at high temperatures –
A challenge
• Need of applications working under harsh
conditions
• Limited use of conventional lubrication methods
FN
Heat
conduction
Adhesion
Diffusion
Thermal
fatigue
2
Abrasion
Vslide
Oxidation
Microstructural
changes
Reduction of
hardness
Significance of the materials investigated
• Boron steel is increasingly used in many
applications such as structural components in the
automotive industry
• These parts are processed through hot metal
forming operations
• Toolox 44 is often chosen as tool material in view of
its good mechanical properties even at elevated
temperatures
3
Wear mechanisms maps- earlier work
Childs, T. H. C., The sliding wear
mechanisms of metals, mainly steels.
Tribol. Int., 1980, 13, 285–293.
Lim, C. Y. H., Surface coatings for cutting
tools. Ph.D. thesis.
Singapore: National University of
Singapore, 1996.
Lim, S. C. and Ashby, M. F., Wearmechanism maps. Acta Metall.,
1987, 35, 1–24.
4
I.A. Inman et al. / Wear 260 (2006) 919–932
Objectives
• To understand wear mechanisms of tool steelboron steel pairs at different temperatures
• To develop a simplified high-temperature wear
map for that material pair
5
Experimental setup
• High-temperature pin-on-disc machine
(Phoenix Tribology TE67)
Chimney
Air
blower
FN
Force
transducer
Pyrometer
6
Experimental work
• Materials
– Prehardened (quenched and tempered) tool steel
• Flat discs (ø75mm x 7.9mm thick) (lower disc specimen)
– Boron steel
• Cylindrical pins (ø4mm x 4mm high) (upper pin specimen)
Material
7
Chemical Composition (wt%)
HV
C
Si
Mn
P
S
Cr
B
Mo
V
Ni
Boron
steel
0.20.25
0.20.35
11.3
max
0.03
max
0.01
0.140.26
0.005
-
-
-
234
Tool steel
0.32
0.61.1
0.8
max
0.010
max
0.003
1.35
-
0.8
0.14
max
1
460
Test Matrix
• Influence of load and temperature
Pin Specimen
Disc
specimen
Temperature (°C)
Pressure (MPa)
Sliding Velocity (ms-1)
2 (25N)
25
4 (50N)
6 (75N)
2
100
4
6
2
Boron steel
Tool steel
200
4
6
2
300
4
6
2
400
8
4
6
0.2
Friction coefficient
Coefficient of friction
1,4
25 N
1,2
50 N
75 N
1
0,8
0,6
0,4
0,2
0
100
200
300
400
Temperature (°C)
9
Average CoF at the steady state region
• For a given load, the CoF decreases as the temperature is
increased
• In general, for a given temperature, the CoF decreases as
the load is increased
Glaze layer formation
Generation of wear
particles
Wear debris
retention
Agglomeration,
compaction and
formation of
compact layers
T
• Reduce metal-to-metal
contact
• Load bearing areas
• Easy to shear
10
Glaze Layer
formation
Sintering
Glaze layer constituents
11
Wear behavior
Strong adhesion
Transfer particle
Wear
particles
Strong adhesion
Sliding direction
Tool steel disc at 25N and 25 °C
• 25N 25 °C
Metal-to-metal contact
Grooves made by
ploughing effect of
transfer particles acting
as two-body abrasive
particles
12
Transfer particle
Sliding
direction
Sliding
direction
Wear behavior
Strong
adhesion
Transfer
particle
Strong adhesion
Sliding
direction
• 75N 25 °C
Bigger grooves made
by the transfer particles
Formation of cracks at
the grooves
Sliding direction
13
Wear behavior
• 25N 100 °C
Formation of isolated
patches of an
oxidised protective
layer
14
Wear behavior
• 50N 300 °C
Smooth and continuous
glaze layer
15
Wear behavior
• 75N 300 °C
Detachment/breaking of
the wear protective
layers
16
Wear behavior
• 25N 25 °C
Grooves made by twobody transfer particles
Transfer particle
Sliding direction
17
Wear behavior
• 75N 25 °C
More and bigger
grooves made by twobody transfer particles
18
Wear behavior
• 75N 300 °C
Formation of more
continuous isolated
wear protective
patches.
19
Wear behavior
• 75N 400 °C
The increased applied load
(50N and 75N) led to the
development of wear protective
layers
20
21
SWR
COF
Development of a wear and friction map
Contact Pressure (MPa)
Specific Wear Rate (mm3*Nm-1)
Specific wear rate and friction map
Temperature (°C)
22
Friction and wear mechanisms map
23
Conclusions
• The frictional behaviour is both, load and temperature
dependant. In general the friction coefficient decreases
as both, temperature and load are increased
• Above 100 °C, development of wear protective layers
on the boron steel pin surface was observed
• An increase in load resulted in breaking-up of the layers
thus increasing the wear rate
• The formation of stable protective wear layers on the tool
steel surface was noticed at temperatures above
200°C.
24
Acknowledgments
• Austrian Comet-Program (governmental funding
program for pre-competitive research) via the Austrian
Research Promotion Agency (FFG) and the TecNet
Capital GmbH (Province of Niederöserreich)
25