Nanoscale Tribology - mbns.bruker.com Tribology Understanding Mechanical and Tribological Surface...

Nanoscale TribologyUnderstanding Mechanical and Tribological SurfaceModification in Lubricated Contacts

Ude Hangen, Ph.D.2018-03-15

Table of Contents

3/15/2018 2Nanoscale Tribology | Bruker

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

Transducer and Performech II ControllerCore Technology


• 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

Transducer Calibration Details


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

Quantitative Measurements by…More Calibration


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

Nanoindentation Testing Principle


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

Predefined Hysitron Load FunctionsOverview of Testing Methodologies Used in this Presentation


• Quasi-static Indentation

• XPM – Fast Mapping

• CMX – Depth Profile • Single Scratch with Ramp Force

• Reciprocating Scratch Testing

Indentation Scratch

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


Click to Play

https://www.hysitron.com/media/142838/engine-video.mp4

Typical Changes in a Tribological Contact


Click to PlayClick to PlayClick to Play

https://www.hysitron.com/media/142841/soft-tribolayer.mp4

https://www.hysitron.com/media/142840/hard-tribolayer.mp4

https://www.hysitron.com/media/142839/changes-in-material.mp4

Interfacing Real Parts on aHysitron TI 980 TriboIndenter


Piston Cylinder LinerPiston

Surface Changes on the Piston


1

3

4

2

Measurements in a Cylinder Liner


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

Reciprocating Scratch Testing


Click to Play

https://www.hysitron.com/media/142842/scratch-video.mp4

TriboImage – Friction and Wear Analysis


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

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


Rolling Friction; No-Slip

Rolling Friction; Negative-Slip

Hardness Dependence on Formation Temp

Hardness

• Indentation Hardness


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

Hardness and Modulus Profile:No-Slip Zone


• 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

Running Surface; Zero-Slip Zone; XPM

In-Situ SPM Image

• 3D-Topography •

• Surface Roughness •


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

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


Roller Bearing

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


Oil Salty WaterEnvironment

Rotating Axis

Courtesy: Lothar Hörl / Uni Stuttgart

Virgin Surface

Worn Surface Side

Worn Surface Center

Investigation on the Surface in Contact


Optical Image of Worn Surface Storage Modulus Distribution

Shift Due to Wear/Aging

Slid

ing

Dir

ecti

on

Width of Contact with Rotating Axis

Cross-Sectional Investigation


Cross-Sections:Worn Surface Video Image

Modulus Mapping:Result

Width of Contact with Rotating Axis

Virgin Surface

EpoxyResin

EpoxyResin



Virgin SurfaceCross-Sections:Worn Surface

EpoxyResin

EpoxyResin

Tan Delta – Distance from Surface

Surface Position



Virgin SurfaceCross-Sections:Worn Surface

Worn

EpoxyResin

EpoxyResin

Tan Delta – Distance from Surface

Surface Position

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.


Nanoscale Tribology - mbns.bruker.com Tribology Understanding Mechanical and Tribological Surface...

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