ICMCTF 2012! - CD-Lab Application Oriented Coating Development

11:20am B6-1-11 Direct current magnetron sputtering of ZrB2 from a
compound target, H. Högberg (hans.hogberg@liu.se), Linköping
University, Sweden INVITED
Transition metal diborides MeB2 are ceramics with high hardness, high
melting points, and high temperature stability. These characteristics
originate from their hexagonal and layered crystal structure, space group
191, where the transition metal atoms constitute the A layers (0,0,0) and the
boron atoms occupy the trigonal prism interstitials (⅓, ⅔, ½) and (⅔, ⅓, ½)
present in the structure. This arrangement enables both strong Me-B bonds
given the electron transfer from the metal atom to the boron atoms and Me-
Me overlap to yield metal-like properties as exemplified by a good
electrical conductivity seen for the transition metal diborides. Furthermore,
the boron atoms will form a covalently bonded honeycombed structured
sheet, in which the electron injection from the metal results in graphitelikes
properties; the sheet sometimes being refereed to as “borophene”. The
above described property envelope suggests many potential applications for
transition metal diborides as thin films ranging from hard protective
coatings to high temperature resistant conductive layers.
For the transition metal diboride ZrB2, we have studied growth at different
conditions of target effect, substrate temperature, substrate bias, base
pressure etc., using sputtering from a compound target in an industrial scale
high vacuum system, CemeCon, CC 800 ® /9 ML as well as growth in a
laboratory scale ultra high vacuum system.
Our results from x-ray diffraction recorded from films deposited on Si(100)
substrates show that 0001 oriented films can be deposited in both type of
systems without external heating of the substrate and at growth rates of ~
3nm per second. Such films are close to stoichiometric, B to Zr ratio of 2 to
2.1, and total level of contaminants less than 2%. Transmission electron
microscopy and scanning electron microscopy images display a columnar
growth mode. Nanoindentation performed on the films show that they are
hard ~20-25GPa and with an elastic recovery of 96%. Four point probe
measurements on films deposited on 1000 Å SiO2/ Si(100) substrates yield
resistivity values in the region of 150 to 180µΩ cm
Increased substrate temperatures affects the preferred 0001 oriented growth
mode by allowing the nucleation of grains with other orientations as 101̅1
and 101̅0, and at temperatures above ~500 o C the deposited films are 101̅1
oriented.
Tribology & Mechanical Behavior of Coatings and
Engineered Surfaces
Room: Tiki Pavilion - Session E2-1
Mechanical Properties and Adhesion
Moderator: M.T. Lin, National Chung Hsing University,
Taiwan, D. Bahr, Washington State University, US, R.
Chromik, McGill University, Canada, W. Clegg, University
of Cambridge, UK
8:00am E2-1-1 Strain hardening behavior in multilayer thin films, D.
Bahr (dbahr@wsu.edu), RL. Schoeppner, S. Lawrence, I. Mastorakos, H.
Zbib, Washington State University, US
Thin film multilayers, where the layer thickness is between 5 and 25 nm,
have been shown to exhibit significant strength enhancements over the
constituent components, appealing for wear resistant coatings. The vast
majority of research in this area has been focused on bi-layer systems (e.g.
Cu-Ni, Cu-Nb). The particular strengthening mechanisms depend on the
interface structure; FCC-FCC interfaces tend to strengthen due to elastic
modulus mismatch while FCC-BCC interfaces do not transmit dislocations
and additionally can provide the ability to shear to accommodate the
presence of dislocations. Additionally, the ability to have locally disordered
interfaces provides a sink for defects due to radiation damage. However,
these high strength materials often do not have substantial ability to sustain
high strains, and their ductility decreases with decreasing layer thickness.
Recently we have demonstrated that tri-layer films, Cu-Ni-Nb, exhibit
additional strain hardening due to the ability to have dislocations in the FCC
layers cross slip because of the presence of the FCC-BCC interface adding
strength to the system. This presentation will demonstrate the use of
nanoindentation techniques to extract strain hardening behavior from thin
films, and compare the results from microtensile behavior of free standing
films with those of the films on oxidized silicon substrates. The hardness
behavior is tracked as a function of included angle of the indenter to
generated different effective strains. The pile up around the indentation is
also tracked to correlate to the strain hardening coefficient. These
complementary techniques are then compared to tensile testing of free
standing, sub-micron thick films using digital image correlation for strain
measurements. A combination of molecular dynamics and dislocation
dynamics is used to demonstrate the likely mechanism which causes this
additional strain hardening behavior.
8:20am E2-1-2 Adhesion of tetrahedral amorphous carbon (ta-C)
coatings deposited on different substrates: Simulations and
experimental verification, N. Bierwisch, Saxonian Institute of Surface
Mechanics, Germany, G. Favaro, CSM Instruments SA, Switzerland, J.
Ramm, OC Oerlikon Balzers AG, Liechtenstein, N. Schwarzer, Saxonian
Institute of Surface Mechanics, Germany, M. Sobiech
(matthias.sobiech@oerlikon.com), B. Widrig, OC Oerlikon Balzers AG,
Liechtenstein
The performance of cutting and forming tools can be significantly improved
by ta-C coatings. Different applications of such tools implicate coating
deposition on different materials. Moreover, the pre-treatment of the tools
to be coated becomes complicated due to the necessity to perform the
deposition at low temperature. Therefore it follows that a procedure to
predict coating adhesion on different substrate materials would be of great
benefit in order to design straightforwardly the coating-substrate system.
In this work, the mechanical properties of ta-C coatings deposited on 1.2842
(90MnCrV8) steel and tungsten carbide (6wt.% Co) have been investigated.
The specific Young's moduli and yield strengths were derived from nanoindentation
measurements, and multi-axial load stress profiles were
simulated accordingly to Ref. [1]. The von Mises and normal stress profiles
obtained from simulations are utilized to predict the locations within the
coating-substrate systems where either the yield strengths or the critical
tensile stresses are exceeded. This prediction is confirmed by scratch tests
for which the load range and indenter geometry is optimized for the depth
of interest by simulation (test dimensioning as elaborated in [1]). On the
basis of these results, it was assumed that stress relaxation could be
significantly dependent of the substrate material (i.e. steel or tungsten
carbide). Therefore, non-destructive X-ray diffraction stress-depth profiling
[2] was used to investigate the near-surface regions of both substrate
materials. Thus, on this basis a straightforward interface design suitable for
particular applications becomes possible.
[1] N. Schwarzer, Q.-H. Duong, N. Bierwisch, G. Favaro, M. Fuchs, P.
Kempe, B. Widrig & J. Ramm: Optimization of the Scratch Test for Specific
Coating Designs, submitted to SCT, accepted August 2011
[2] A. Kumar, U. Welzel & E.J. Mittemeijer: A method for the nondestructive
analysis of gradients of mechanical stresses by X-ray diffraction
measurements at fixed penetration/information depths, J. Appl. Crystal. 39,
633, 2006
8:40am E2-1-3 Analysis on the stress transfer and the interfacial
strength of carbon coatings on metallic substrate using in-situ tensile
and nanobending experiments in SEM and Raman spectroscopy., K.
Durst (Karsten.Durst@ww.uni-erlangen.de), University Erlangen-
Nuernberg, Germany INVITED
The interface between a coating and a substrate is often crucial for the
performance of coating systems. During deformation of the substrate, shear
stresses are transferred at the interface into the coating, leading there
eventually to cracking and delamination. In this work, the properties of
carbon coatings on ductile metallic substrates (diamond on Ti and a:C-H on
steel) are studied, using new in-situ methods for analyzing the stress
transfer as well as the interfacial strength of the coating in dependency of
the microstructure and the local chemical composition.
The first part of the talk is concerned with the analysis of the stress transfer
from a ductile Ti-substrate to a brittle diamond coating under tensile
straining using micro-Raman spectroscopy and analytical modeling. The
coating contains initially compressive residual stresses of ~-5.4 GPa, which
turn into the tensile regime during plastic straining of the substrate. Once
the fracture strength of the coating of ~1.5 GPa is reached, normal cracks
appear in the coating followed by a reduction in crack spacing and finally
delamination. The stress measurements across different cracked coating
segments using Raman spectroscopy, indicated tensile stresses at the middle
and compression near the edges of the segment under tensile load. Coating
fragmentation leads to a relaxation of the stress within the cracked coating
segment. Further cracking of the smaller segments requires larger strains.
The classical shear lag model is extended to derive the stress distribution in
the coating bonded to the substrate, considering both residual stress and
cracking using a fracture criterion. The model captures nicely the failure
behavior of the coating as well as the stress profiles in cracked coating
segments.
In the second part of the talk two a-C:H-coating systems on steel with the
same microstructure, but different adhesion layers and qualitative different
adhesion behaviour were investigated. The coatings were characterized in
terms of their mechanical properties, microstructure and the chemical
composition using nanoindentation tests and Auger electron spectroscopy
on small angle cross sections of the a-C:H-coatings. There strong gradients
77 Thursday Morning, April 26, 2012