nanoscale tribology - mbns.bruker.com tribology understanding mechanical and tribological surface...
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Nanoscale TribologyUnderstanding Mechanical and Tribological SurfaceModification in Lubricated Contacts
Ude Hangen, Ph.D.2018-03-15
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Table of Contents
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1. Introduction: Brief overview of nanoindentation and nanoscratch testing
2. Discussion of typical changes found in a combustion engine:
a. Nanomechanical testing to understand materials changes
b. Cyclic scratch testing to simulate a single asperity in a sliding contact
3. Applications: Investigation of surface changes in a roller bearing due to the
formation of a tribolayer and in a rubber-gasket sliding on a rotating axis
4. Conclusions and Q&A
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Transducer and Performech II ControllerCore Technology
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• Load or Displacement Control • 78 kHz Feedback Loop Rate• 38 kHz Data Acquisition Rate• Experimental Noise Floor <100nN (Digital Controller)• Enhanced Testing Routines• Digital Signal Processor (DSP) + Field Programmable
Gate Array (FPGA) + USB Architecture• Modular Design
• Capacitive displacement sensing• Small inertia of moved parts <1 g• Low intrinsic dampening
Transducer Stability Specs
• 0.1nm displacement noise floor
• 20nN force noise floor
• <0.05nm/sec thermal drift
*Specs Guaranteed On-Site*
Enabling Technology for Ultra-Small Materials Research
Indenter
Center Electrode
Outer ElectrodeSprings
Outer Electrode
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Transducer Calibration Details
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1D Transducer
(Indentation + Imaging)
2D Transducer
(Indentation + Scratch + Imaging)
• Transducer ► Displacement: Indentation and Scratch (in the factory)
❖ SI traceable calibration by measuring the indenter displacement with an interferometer
• Transducer ► Force: Indentation and Scratch (in the factory)
❖ SI traceable calibration by hanging a set of 5 weights to the indenter
• The plate spacing, electrode area, and spring constants of the center plate areconstant in time and the factory calibration is therefore maintained during the shipments
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Quantitative Measurements by…More Calibration
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Area Function
• Calibrated Tip Geometry
• Diamond Probes
• Indenting into a standard reference material (fused quartz), with a known Er, the contact area is determined for each indent
• The contact depth of the indents is also measured directly from the force-displacement curve
• Several indents at different depths will yield different contact areas and a Tip Area Function can be generated
Starting from:
Re-arranged:
c
rA
SE
2
S
Phhc
maxmax
𝐴𝑐 =𝑆2π
4𝐸𝑟2
&
Tip Area Function:
Berkovich Cube Corner Conospherical
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Nanoindentation Testing Principle
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Surface with Indentation Cup A
PH
A
SEr
2
Reduced Modulus Hardness
Penetration Depth
Contact Area
Reduced Modulus
12
1
1
25.24
i
c
N
i
ic hChA
s
s
i
i
r EEE
22111
S
Phhc
maxmax
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Predefined Hysitron Load FunctionsOverview of Testing Methodologies Used in this Presentation
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• Quasi-static Indentation
• XPM – Fast Mapping
• CMX – Depth Profile • Single Scratch with Ramp Force
• Reciprocating Scratch Testing
Indentation Scratch
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Engineering of Parts in Relative Motion
Tribology:
• The science of sliding or rolling parts in
relative motion
• The power train of automobiles includes a
number of engineering solutions to
minimize friction and wear between sliding
parts and optimize energy consumption
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Click to Play
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Typical Changes in a Tribological Contact
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Click to PlayClick to PlayClick to Play
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Interfacing Real Parts on aHysitron TI 980 TriboIndenter
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Piston Cylinder LinerPiston
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Surface Changes on the Piston
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1
3
4
2
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Measurements in a Cylinder Liner
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Bruker‘s Hysitron instruments allow interfacing real parts for testing. The image below shows the mechanical testing setup on the surface of a sectioned DLC coated cylinder liner.
Hysitron TI 980 TriboIndenter
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Reciprocating Scratch Testing
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Click to Play
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TriboImage – Friction and Wear Analysis
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Intact 2, 12cm
Segment
Positio
n
Fric
tio
n S
cale
Intact 1, 10cm
Worn 4, 9cm
Worn 3, 6cm
Worn 2, 4cm
Worn 1, 2cm
0.23
0.22
0.18
0.17
0.17
0.13
Average Friction Coefficient
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Roller Bearing – Formation of Tribolayer
• A tribolayer is formed in the contact of the roller and the flat liner, the measurements are performed onthe liner
• The tribolayer plays an important role to protect the roller from wear effects
• The rolling motion is superimposed with changing amounts of slip depending on the position on the roller
• The resutling surface roughness and structure as well as the mechanical properties play an important role during the formation of the layer and for its stability
• Bruker‘s Hysitron instruments are able to assess these properties in the relevant range
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Rolling Friction; No-Slip
Rolling Friction; Negative-Slip
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Hardness Dependence on Formation Temp
Hardness
• Indentation Hardness
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Coefficient of Friction
• Locally Tested by Nanoscratch
0.22
0.23
0.24
0.25
0.26
0.27
0.28
0.29
0.3
80 ℃ 100 ℃ 120 ℃
Co
effi
cie
nt
of
Fric
tio
n
High slip zone outside no slip zone High slip zone inside
0
2
4
6
8
10
12
14
80 ℃ 100 ℃ 120 ℃
Ave
rage
Har
dn
ess
(GPa
)
High slip zone outside no slip zone High slip zone inside
• Bearing: 81212 Schaeffler
• Additive: ZDDP
F.Pape et al.: Investigation of the temperature influence on the formation of boundary layers on bearings; Tribologie + Schmierungstechnik; 68.Jahrgang – 5/2017
• Axial Load: 60kN
• Test Length: 50 – 200h
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Hardness and Modulus Profile:No-Slip Zone
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• CMX-load function used for depth profiling
• The average depth profile of 6 indentation curves on each sample shows a soft tribolayer surface supported by a strong steel substrate
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Running Surface; Zero-Slip Zone; XPM
In-Situ SPM Image
• 3D-Topography •
• Surface Roughness •
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Modulus Contour Map
Distrubution measured by 10,000 indentations at
30nm penetration depth
Hardness Contour Map
Local variation of resistanceto plastic deformation
Correlation of Surface Structure and Mechanical Properties
F.Pape et al.: Investigation of the temperature influence on the formation of boundary layers on bearings; Tribologie + Schmierungstechnik; 68.Jahrgang – 5/2017
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XPM – Tribolayer in Roller Bearing
• Tribolayer has approximately 50-100nm thickness
• Indentation depth 20nm: surface layer is soft
• Indentation depth 150nm: underlying steel substrate is hard
• 2 mappings – 10x300 nanoindentation tests
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Roller Bearing
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Rotating Axis Sealed with aRubber Gasket
• The natural rubber with carbon black
and other filler materials is wearing in
the contact area with the rotating axis
• The changes and the aging can be
observed by nanoindentation and
modulus mapping
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Oil Salty WaterEnvironment
Rotating Axis
Courtesy: Lothar Hörl / Uni Stuttgart
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Virgin Surface
Worn Surface Side
Worn Surface Center
Investigation on the Surface in Contact
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Optical Image of Worn Surface Storage Modulus Distribution
Shift Due to Wear/Aging
Slid
ing
Dir
ecti
on
Width of Contact with Rotating Axis
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Cross-Sectional Investigation
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Cross-Sections:Worn Surface Video Image
Modulus Mapping:Result
Width of Contact with Rotating Axis
Virgin Surface
EpoxyResin
EpoxyResin
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Cross-Sectional Investigation
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Virgin SurfaceCross-Sections:Worn Surface
EpoxyResin
EpoxyResin
Tan Delta – Distance from Surface
Surface Position
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Cross-Sectional Investigation
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Virgin SurfaceCross-Sections:Worn Surface
Worn
EpoxyResin
EpoxyResin
Tan Delta – Distance from Surface
Surface Position
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Summary – Controlling Friction and Wear
• Friction and Wear are processes that strongly relate to the first nm to 200nm layer under the surface.
• Nanoindentation and Nanoscratch are perfectly suited for studying the local changes due to tribological processes.
• Nanoindentation and Nanoscratch are complementary to tests that are mimicking the real parts wear.
• Indentation and Scratch with nm depth focuses on the surface changes and allows to enter a new scale of testing when combined with in-situ imaging.
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