Instrumented Indentation - CSM Instruments

Advanced mechanical surface testing by
Nanoindentation
Technical Workshop
Brescia, 17.04.2012
Fanny Ecarla

Agenda
Introduction –
Classical Hardness vs
Principle of Instrumented Indentation
Instrumented Indentation
Advance measuring modes, analysis and challenges of
Instrumented Indentation
Key features of CSM Indentation Tester – Surface Top
Referencing

Classical hardness measurement
//// Drawbacks
> All classical hardness measurement are
based on manual optical measurements
> No automatic calculation of hardness from
several indentations
> At low loads resolution limits of the optical
microscope are reached (imprint is too small
for precise diagonal measurement)
> Minimum penetration depths �1 to 2�m

Principle of Instrumented Indentation

Why the Nanoindentation?
> On a surface covered by thin layers, the
maximum depth of the indentation must be
lower than 10% of total depth of the
covering
substrate.
to avoid influence on the
Film depth, h film
Maximum penetration, h m
Elastic distortion
h
h
m �
film
10%
> High resolution positioning:
- Small volume testing
- High positioning accuracy
10�m

What is the Instrumented Indentation
> Instrument which provides the ability to measure the indenter depth
penetration, h, under the applied force, F, throughout the testing
cycle.
> It is capable of measuring both the plastic and elastic deformation of
the material under test.
F
N
Sample
XY Table
Load Actuator
(coil/magnet)
Displacement Sensor
(capacitive gauge or LVDT)
Reference

Instrumented indentation: not only hardness
//// Information revealed from Nanoindentation Testing:
> Hardness (instrumented, recalculated Vickers hardness)
> Elastic modulus
> Storage & loss modulus (polymers)
- Depth profiles (hardness, Elastic modulus, storage & loss modulus)
> Elastic/plastic energy ratio (measure of elasticity)
> Fracture toughness (brittle materials)
> Creep
> Stress-strain curves (analogy to tension tests)
> …etc.

Indentation Tips
Berkovich (142.3°)
Conical (R < 3 µm)
Vickers (136°)
Cube Corner (90°)
Conical (R > 3 µm)

Pyramid indenters
Projected contact area For pyramidal indenters
A p
(vickers) = Ap (berkovich)
Same h

Load-Displacement Data
Comparison of elastic, perfectly plastic, and elastic-plastic
contact characteristics
Stress-Strain
curves
Indentation
curves
Indentation
prints
�
F
Elastic
�
h
�
F
Plastic Elastic - Plastic
�
h
�
F
�
h

Calculation of Hardness (H IT )
The maximum applied force Fm is obtained by the load and unload
curves
The projected contact area is established by the contact point.
Hardness �
H �
IT
Fm
Ap
F m
Applied Load
Depth

Calculation of Elastic Modulus (E IT )
> Similar procedure as for hardness calculation:
1. fit of the loading/unloading curve
2. determination of the slope S
3. determination of the contact depth h c (the depth
corresponding to contact of the material with the
indenter, not the maximum depth)
4. calculation of projected contact area A p at contact
depth
5. calculation of reduced modulus E*
6. knowing Elastic modulus of the indenter
(diamond) we can calculate Elastic modulus of the
coating EIT Reduced modulus
*
E
IT
�
π
2
S
A p
S stiffness
Ap projected contact area
Eit, � Elastic modulus/Poisson’s ratio of the coating
Ei, �i Elastic modulus/Poisson’s ratio of the indenter
F m
Load, F
Depth
, h
E
it
*
it
h
p
h
r
hs =
�.(hm–hr h
2
1��
�
2
1 1��
� i
E E
c
S
Elastic modulus (E IT )
i
)
h
m

Experimental procedure
F m
Measure F m and h t
Calculate
Hardness
Calculate
Reduced
Modulus
E
*
IT
h t
F
HIT �
A
�
�
2
m
p
S
A
p
Calculate
Modulus
F m
1
E
*
IT
A
p
�
0
2
c
1
2
h
c
�
h
t
Fm
� �
S
Calculate
Contact Depth
� C h � C hc
� C hc
� C hc
Calculate Projected Area of Contact
( 1
2
� � ) ( 1 � �
�
E
E IT
S
ht Calculate Stiffness
i
2
i
)
1
2
3
1
4
� ...

Advanced modes and analysis

Indentation Software
Load
Type of test
Standard Multicycle CMC Sinus
Time
Type of array
Load
Time
Simple Line Matrix
Load
Time
Load
Time

Indentation Software
Standard test
One Indentation
One measure of H IT & E IT
Load
Time

Indentation Software
CMC (Continuous Multi Cycle)
Each cycle gives H IT and E IT
Load
Time
Same position
Increasing load at each cycle

Indentation Software
Sinus (DMA)
Load
Time

Dynamic Mechanical Analysis:
Sinus Mode
Force
A small amplitude force oscillation is superimposed onto the
applied load signal and the resultant displacement amplitude
measured. This method is very useful in revealing information
about storage and loss modulus.
Time
Force
Time

Dynamic Mechanical Analysis: Sinus Mode
The viscous character of the material introduces a phase angle
φ between the force and displacement signals:
ho
Force
�
Time
ho
Displacement

Visual Matrix

Visual Indentation
Direct calculation of hardness from the loading / unloading curve:
possibility of automated measurements
(matrix/advanced visual matrix)
No need for optical measurement of dimension of the imprint
Directly measured penetration depth: to avoid influence by the
substrate

Fracture Toughness
Pure Silicon
K
1
�
� � E
� �
� �
�
� � H
IT
IT
�
�
�
�
1/
2
�
�
� P
�
��
��
c
3
2
�
�
�
�
TiN on 440C steel
c

Creep
>
>
Force, F [mN]
In an indentation test, creep often manifests itself as a bowing out
or “nose” in the unloading portion of the force-displacement curve.
For such material, when the force is held during a certain time at
the maximum force, the indenter continues to penetrate.
1.2
0.8
0.4
0
Hold period of 120s
No hold period
0 200 400 600
Indentation depth, h [nm]
Nose
PMMA 1mN force
Loading rate 2mN/min

Influence of Surface Roughness

Influence of Surface Roughness
>
>
Surface roughness is extremely important in Instrumented
Indentation Testing because mechanical properties of the
tested material are calculated on the assumption that the
sample surface is flat.
Because the IIT technique uses the measured indentation
depth to estimate the residual contact area and subsequently
calculate the hardness, the surface roughness can have a
significant influence on the resultant values.

>
//// Influence of Surface Roughness
When the indenter comes into contact with a peak, the non-uniform
contact increases the localized stress at the points of contact,
deforming the material to a greater depth at relatively low loads.
This can result in a greater penetration depth and lower calculated
hardness.
When the indenter comes into contact with a valley, the true
contact area is underestimated and consequently, the calculated
hardness is overestimated.

Influence of Surface Roughness
Ra=5nm
Ra=167nm

Influence of Surface Roughness
>
>
It is imperative to know the condition of a surface before
proceeding with an instrumented indentation test.
The International Standard ISO 14577-4 stipulated that the Ra
value should be less than 5% of the maximum penetration
depth.

Influence of Surface Roughness

Nanoindentation in Liquid

Nanoindentation in Liquid
Simple NHT modification for in-situ liquid testing
All NHT technical specifications are maintained

Nanoindentation in Liquid
Standard NHT
Modified NHT
NOTE: The holes in the extension allow liquid to circulate around indenter without any
risk of entering the head

Key Features of CSM Indentation Testers
Top Surface Referencing

Instrumented Indentation
General Principle
F N
Sample
XY Tables
Load Actuator
(coil/magnet or
Electrostatic)
Displacement Sensor
(capacitive gauge or LVDT)

Instrumented Indentation
Thermal drift
Depth variation

Instrumented Indentation
Table play, sample drift or compression
Depth variation

CSM Indentation: Instrumented Indentation
CSM Principle
F N
Sample
XY Tables
Load Actuator
(coil/magnet)
Displacement Sensor
(capacitive gauge or LVDT)
Reference (ring or fork)

CSM Principle
Thermal drift
Depth stable

CSM Principle
Table play, sample drift or compression
Depth stable

Top Referencing
Effective compliant material is of the order of a few millimeters in
length, between the surface and the depth sensor
6 mm
Sample

Top Referencing
The reduction in the length of the compliant material between
the surface and the depth sensor leads to greater accuracy in
the measurement.
Sample

CSM Nanoindentation
Unique referencing technique by CSM Instruments
> Unique thermal stability
> High Throughput
> Reliability
> Functionalities
> The most easy-to-use nanoindentation system

Ultra Nanoindentation Tester

FN
Ultra Nanoindentation Tester (UNHT)
Feedback loop
on force sensor
Load-depth curve
Dz
Indenter Loading Unloading Contact
A1
I
sample
Stage
A2
R
A1 & A2:
piezoelectric
actuators
Reference contact
Motorized
Feedback loop
for accurate low
force sensing
Z table

Indentation depth, h [nm]
UNHT Stability During Measurement
h [nm]
91
90
89
100
80
60
40
20
0
33 83 133 183 233 283 333
Time, t [s]
0 50 100 150 200 250 300 350
Time, t [s]
Fused Silica 1mN force
1.5
1.2
0.9
0.6
0.3
0
Depth variation
less than 1nm
over 5 minutes
Force, F [mN]

Force (µN)
120
100
80
60
40
20
0
5 nm indentation on DLC film
Noise floor less than 0.1 nm!
Single Indent
0 1 2 3 4 5 6
Pentration Depth (nm)

Thank you for your attention