SLIDE 1
Marco Sebastiani FIB user group 2014
RESIDUAL STRESS ANALYSIS ON A MICRON-SCALE
Intra-grain stress analysis in polycristalline alloys and TBCs Thin coatings and MEMS
2
R ESIDUAL STRESS MEASUREMENT BY FIB A controlled removal of a small - - PowerPoint PPT Presentation
R ESIDUAL STRESS MEASUREMENT BY FIB A controlled removal of a small - - PowerPoint PPT Presentation
F OCUSED I ON B EAM TECHNIQUES FOR RESIDUAL STRESS ANALYSIS AT THE MICRON - SCALE Marco Sebastiani University of Rome Roma TRE Engi nee ri ng Department Materials Science and Technology Group 7th Annual FIB SEM Workshop Thursday, February 27th,
SLIDE 2
SLIDE 3
Marco Sebastiani FIB user group 2014
GAP OF KNOWLEDGE
Research needs Many advanced materials and devices require
stress measurement with sub-micrometer 3D spatial resolution
Existing high resolution methods (i.e. using
synchrotron XRD, EBSD) are very expensive, time consuming and not suitable for amorphous materials
Production needs New developed procedures should also be
dow ngradable to in-line quality control processes, or at least cost-saving with respect to traditional high resolution characterisation techniques.
Innovative HR resolution should be standardised.
3
SLIDE 4
Marco Sebastiani FIB user group 2014
RESIDUAL STRESS MEASUREMENT BY FIB
A controlled removal of a
small material volume is performed by FI B at low ion current (10-100 pA);
The attendant relaxation
strain is then measured, step-by-step, by Digital I m age Correlation ( DI C) techniques;
The residual stress (in –plane
distribution and depth profile) is then calculated from the measured strain by using either analytical or Finite Elem ent m odelling
4
SLIDE 5
Marco Sebastiani FIB user group 2014
I MPLEMENTATI ON OF FI B- DI C PROCEDURES
Focused I on Beam controlled material removal, by the ring-core milling geometry
- Geometries
- Surface patterning
- FIB milling parameters
- SEM imaging parameters
Digital I m age Correlation for strain measurement
- 2D strain mapping;
- Control of SEM noise
- Best patterning for DIC
- GUI
Residual stress calculation
- FEM of influence functions for
several geometries
- Models to correct for Elastic
anisotropy
- FEM for through-thickness
stress gradient analysis;
5 5
SLIDE 6
Marco Sebastiani FIB user E gF ro Uu G p 2014 3
FIB MILLING GEOMETRIES
Ring-core method Materials Letters 63 (2009) 1961–1963 Slot-milling method Thin Solid Films 443 (1-2), pp. 71-77 Hole drilling method Nanotechnology 17, Number 20 , 2006 H-bar Micro-cantilever method
Acta Materialia 57 (6), 2010
Surface & Coatings Technology
6
215 (2013) 247–252
SLIDE 7
Marco Sebastiani FIB user group 2014
KEY-WORD FOR INDUSTRY: AUTOMATION
The whole test sequence is
completed in ½ hour and multiple test positions can be set for overnight testing;
DIC is performed live during
test
Only preliminary alignment
and focus is required to the
- perator
E-beam Pt deposition of
surface features
Automated
patterning/imaging/milling
0° and 52° imaging after
each milling step
Automated Correction of
ion/electron drift during the test;
All test are initially set
through a GUI
Geometry Size SEM/FIB parameters 7
SLIDE 8
Marco Sebastiani FIB user group 2014
8
NEW PATTERNING STRATEGIES FOR IMPROVED DIC
Reduced influence of the
Pt-pad
Full strain map over the
X-Y plan
Best strain measurement
along the fast-scan direction
More effective DIC
(resolution of 1/1000 pixel) Freeware DIC runnign
- n Matlab (C. Eberl)
SLIDE 9
Marco Sebastiani FIB user group 2014
RESIDUAL STRESS CALCULATION PROCEDURES
𝑪𝝉 = 𝜻 ⇒
- 10
- 20
- 30
- 11
- 21
- 31
- 2
2
- 3
2
- 3
3
𝜏0 𝜏1 𝜏2 𝜏3
- 1
=
- 2
- 3
=
- r
= 𝜏
⋅
- 1 ≤ ≤ ≤
3
=0
SLIDE 10
Regularisation algorithms for stress depth profile
calculation
9
SLIDE 11
Marco Sebastiani FIB user group 2014
THE ISSUE OF DEPTH MEASUREMENT
We need to develop accurate calibration
procedures for depth measurement.
This is critical in view of an effective residual
stress depth profile.
10
SLIDE 12
Marco Sebastiani FIB user group 2014
APPLICATION TO THIN FILMS FOR AVERAGE
STRESS AND STRESS GRADI ENT ANALYSIS IN THIN FILMS
- M. Sebastiani, C. Eberl, E. Bemporad, G. M. Pharr
Materials Science and Engineering A, 2011
3 µm CAE-PVD CrN on steel AISI M2
11
SLIDE 13
Marco Sebastiani FIB user group 2014
CRITICAL ISSUES FOR STRESS DEPTH PROFILING
DIC is performed LIVE
during the test (e.g. during FIB milling after each SEM imaging step);
Performing AT LEAST five
test in a reasonable amount of time (1/2 day)
DEPTH MEASUREMENT is a
very critical issue in view of the full automation of the method!
12
SLIDE 14
Marco Sebastiani FIB user group 2014
DEPTH PROFILING OF RESIDUAL STRESS: CrN
Strategy for stress gradient calculation: fitting with a polynomial expression of the strain data for h/d<0.3 Calculation of the residual stress DEPTH PROFILE by FEM analysis (Integral
Method)
Significant gradient of
stress is observed from surface to interface on this CrN
13
coating
SLIDE 15
Marco Sebastiani FIB user group 2014
LOCAL RESIDUAL STRESS FIELD IN THIN FILMS
The results consistently show a significant modification of the LOCAL residual stress field induced by the droplet
14
Surface and Coatings Technology, 2013
SLIDE 16
Marco Sebastiani FIB user group 2014
LOCAL RESIDUAL STRESS FIELD IN THIN FILMS
How to explain the
- bserved differences:
(i) an additional thermal stress factor given by the presence of a metallic droplet (ii) the induced coating re- nucleation process and modification of the growth mechanisms in correspondence of the defect
15
Surface and Coatings Technology, 2013
SLIDE 17
Marco Sebastiani FIB user group 2014
APPLICATION ON SUSPENDED MICRO-BRIDGES (MEMS – RF SWITCHES)
Sebastiani, M., Bemporad, Korsunsky, A.M. (2010) AIP Conference Proceedings, 1300,
16
SLIDE 18
APPLICATION ON SUSPENDED DOUBLE CLAMPED
MICRO-BRIDGES
del
- 400 m-
ETD LIME Un1RomaTRE
Sebastiani, M., Bemporad, Korsunsky, A.M. (2010)
AlP Conference Proceedings, 1300,
SLIDE 19
"0
100
T
!
'
- '
APPLICATION ON SUSPENDED MICRO-BRIDGES
RF SWITCHES
500
......., 450
lU
Stress variation over the suspended membrane
Q.. 400
!.
350
(/) (/) (II
.t .....
300 1 250
(/)
jij 200
:J 150
"Cii
f
(II
et::
50
y ' ' ' ' ' '
100
200 300 400 : 500 600 700 800 Di s ' nce from one ' e of the ' e (urn)
ta
:sid
'
membran
SLIDE 20
Marco Sebastiani FIB user group 2014
APPLICATION ON AMORPHOUS PLASMA SPRAYED
SINGLE-SPLATS (APPLICATION IN TBCS)
Sebastiani, M., Bolelli, G., Lusvarghi, L., Bandyopadhyay, P.P., Bemporad, E. Surface and Coatings Technology, 206 (23), pp. 4872- 4880
19
SLIDE 21
Marco Sebastiani FIB user group 2014
APPLICATION TO AMORPHOUS MATERIALS
Al2O3
Single splats
- btained by
plasm a spraying
Surface and Coatings Technology, 206 (23), pp. 4872-4880
20
SLIDE 22
·n;
..
2.SE-03
Al203 splats: Relaxation strain from ring-core incremental
milling
- Test-1
·c
n : ;
....
Ul
c: ....
,
> <
q; 2.0E-03 l.SE-03
l.OE-03
- _-
.{ .
..
- - --
- Test-2
- Test-3
......
- Test-4
- Test-1on small splat
without cracking
- Test-2
- n small splat
without cracking
- ---- Polynomial fitting
S.OE-04
- ::::<:0
- ---6
O.OE +OO :.::....._.u...
- ---"'
200 400 600
Millin
g depth from surface ( nm )
- Small splats (no cracks)
- Interpolated strain at 400 nm: +0.38·1o-3 ± 0.20·1o-3
- Average residual stress: -105.3 ± 55.4
- Elastic modulus by nanoindentation
SLIDE 23
Marco Sebastiani FIB user group 2014
CONCLUSIONS – FIB/DIC METHOD 1/2
A TOOL for micron-scale 3D residual stress
analysis on a micron scale has developed and
- ptimized.
Good results The adopted geometry gives high depth resolution
(≈ 1 00 nm ) and lateral spatial resolution (≈ 1 µm )
The developed milling strategies have improved the
repeatability and robustness of DIC procedures
LIVE strain depth profiling during FIBing and semi-
automated procedure
Calculation of the through thickness stress profile;
22
SLIDE 24
Marco Sebastiani FIB user group 2014
CONCLUSIONS – FIB/DIC METHOD 2/2
Critical issues to be solved Full automation of the procedure. Does the FIB induces additional stresses?? Microstructure/anisotropy/plasticity effects?? Careful analysis of elastic properties for stress
calculation.
Cross validation with other high-resolution methods
(synchrotron-XRD, EBSD, µ-Raman).
Ongoing work: establishm ent of a
standardization activity through a European large project
23
SLIDE 25
Marco Sebastiani FIB user group 2014
ISTRESS EUROPEAN PROJECT
EU project “I STRESS” has started on Jan 1 st 2 0 1 4 Pre-standardization of incremental FIB micro-milling for intrinsic
stress evaluation at the sub-micron scale
A new VAMAS TW A and project liaisons with CEN TCs are going to
be established
24
SLIDE 26
Marco Sebastiani FIB user group 2014
ISTRESS PROJECT
Som e info at this w ebpage: http://www.stm.uniroma3.it/iSTRESS MANY OPEN POSITIONS WITHIN THIS PROJECT: W E ARE LOOKI NG
FOR FI B EXPERTS TO W ORK I N THE CONSORTI UM!
http://www.stm.uniroma3.it/iSTRESS/Pages/Careers.aspx WE ARE LOOKING for associated partners to be involved in the
ROUND-ROBIN activities.
seba@stm.uniroma3.it
The STM group at Roma TRE:
- prof. Edoardo Bemporad prof.
Fabio Carassiti Daniele De Felicis Marco Renzelli Federico Massimi Riccardo Moscatelli
25