ICMCTF 2012! - CD-Lab Application Oriented Coating Development

eproducibility of the preparation of these unique materials. The emphasis
of our presentation will be, however, on the future ways which will assure
the reproducible preparation of nc-TiN/a-Si3N4 and related nanocomposites
in dedicated laboratory apparatuses as well as in large-scale industrial
coating equipment, which will assure achieving high hardness, high
resistance against brittle fracture, high thermal stability and oxidation
resistance.
[1a] www.ibisonline.com.au/IBIS_News/PressReleaseAug11.pdf
[1b] A.C. Fischer-Cripps et al., submitted, as quoted in Ref. [1a]
[2] S. Veprek et al., Thin Solid Films 476 (2006) 1
3:10pm E2-2-6 An expression to determine the Vickers indentation
fracture toughness of Fe2B layers obtained by the finite element
method, A. Meneses-Amador, Instituto Politecnico Nacional, Mexico, I.
Campos-Silva (icampos@ipn.mx), SEPI ESIME Zacatenco, Mexico, J.
Martinez-Trinidad, Instituto Politecnico Nacional, Mexico, S. Panier, Ecole
des Mines de Douai, France, G.A. Rodriguez-Castro, A. Torres-Hernàndez,
Instituto Politecnico Nacional, Mexico
A reverse analysis of the Vickers indentation fracture toughness was carried
out to derive a numerical expression to estimate the fracture resistance of
Fe2B layers. The boride layers were formed at the surface of AISI 1018
steels by developing the powder-pack boriding process at temperatures of
1193 and 1243 K with 4, 6 and 8 h of exposure for each temperature. From
the set of experimental conditions of boriding process, Vickers indentations
were performed with applied loads of 0.49, 0.98, 1.96, and 2.9 N at 15 and
30 microns from the surface of borided steels, respectively. The crack
lengths created from the corners of the Vickers indentation prints were
analyzed in the Palmqvist crack regime with the aid of dimensional analysis
and finite element method (ABAQUS software program), considering the
residual stress field generated by the indentation loads in the boride layer.
The numerical expression of the fracture toughness of the Fe2B layer was
estimated by the superposition technique, where the fracture resistance is a
function of the elastoplastic properties of the layer, and with different crack
lengths superimposed according to the residual stress field caused by
Vickers indentation loads.
The results of the fracture toughness of the Fe2B layer estimated by the
finite element method were compared with the values obtained by
traditional Palmqvist crack models proposed in the literature.
3:30pm E2-2-7 Mechanical properties of FeB and Fe2B layers
estimated by Berkovich nanoindentation on tool borided steels, G.A.
Rodriguez-Castro, Instituto Politecnico Nacional, Mexico, I. Campos-Silva
(icampos@ipn.mx), SEPI ESIME Zacatenco, Mexico, E. Chávez-Gutiérrez,
J. Martinez-Trinidad, I. Arzate-Vázquez, A. Torres-Hernàndez, Instituto
Politecnico Nacional, Mexico
In this study the mechanical behavior of FeB and Fe2B layers formed at the
surface of AISI D2 steels was estimated by Berkovich nanoindentation
technique. The boriding of AISI D2 steels was developed by the powderpack
method at temperatures of 1223, 1273 and 1323 K in the range of
exposure times of 3 - 7 h for each temperature. The mechanical
characterization was performed related to the set of experimental
parameters of boriding process and considering two procedures: first the
nanoindentations were performed along the depth of surface layers with a
constant load of 250 mN to determine the hardness gradient and the state of
thermal residual stresses in the boride layers. In addition, applied loads in
the range of 10 to 300 mN were carried out in the “pure” zone of the FeB
layer at 10 microns from the surface, and in the “pure” zone of the Fe2B
layer (40 microns), respectively.
The results showed, for a constant load of 250 mN, that the state of thermal
residual stresses and hardness of both FeB and Fe2B layers are a function of
the temperature and exposure time of the process, where the hardness
decreases due to the presence of grain coarsening in the surface layers at a
temperature of 1323 K with more than 5 h of exposure. Moreover, the
presence of the indentation size effect (ISE) in the FeB and Fe2B layers was
verified in the range of applied loads, in which the apparent or real hardness
was estimated by traditional models according to the boriding experimental
parameters. Finally, the fracture resistance and brittleness of the boride
layers was evaluated in the range of nanoidentation loads as a function of
boriding temperatures and exposure times; the estimated values are in the
range of 1.36-2.82 and 1.98-3.80 MPa m 1/2 , with the presence of
compressive stresses in the range of 162 to 1604 MPa for the FeB and Fe2B
layers, respectively.
3:50pm E2-2-8 Measurement of Fracture Toughness on TiN thin film,
A.N. Wang, G.P. Yu, J.H. Huang (jhhuang@mx.nthu.edu.tw), National
Tsing Hua University, Taiwan
This research was in an attempt to develop a new method without applying
external stress for measuring fracture toughness of transition metal-nitride
thin films. TiN thin film was selected to be the model material, owing to its
well-characterized mechanical properties and appropriate elastic isotropy.
At present, there has been no standard methodology or test procedure for
assessing the fracture toughness of hard coatings. Previous literatures have
proposed various approaches on the measurement of fracture toughness,
which can be divided into two categories: stress based or energy based.
However, those methods need to design special specimen geometry because
of the requirement in producing valid pre-cracks, and thus the substrate
effect cannot be eliminated. In addition, special stages are often needed to
externally apply stress, which increases the difficulty of the test methods.
TiN thin films deposited by PVD methods normally have high residual
stress which can be controlled by adjusting deposition parameters and
measured nondestructively. Instead of externally applying stress, the
residual stress was utilized in the assessment of fracture toughness. From
Griffith's criterion, energy stored in the film due to elastic mismatch strain
can be released by the formation of cracks. The difference in stress states
before and after crack initiated was used to evaluate the average energy
release rate, from which fracture toughness can be calculated by fracture
mechanics. This method involved residual stress measurement by laser
curvature technique and elastic modulus measurement by nanoindentation
according to ISO 14577-4:2007.
The Poisson’s ratio of single-crystal TiN was used. The results were
compared with those obtained from other techniques and the strong and
weak points of this method were discussed.
4:10pm E2-2-9 Bi-phase Ceramic Composite through Interpenetrating
Network, E.H. Kim, J. Lee, Y. Jung (jungyg@changwon.ac.kr), Changwon
National University, Republic of Korea
SiO2 phase has been infilterated into porous Al2O3 matrix to enhance the
mechanical properties of matrix through interpenetrating network (IPN)
method. In this work, in order to increase the addition effect of SiO2 phase
into the Al2O3 matrix two types of SiO2 precusor were used: tetraethyl
orthosilicate (TEOS) of the silicate type; and polydimethyl siloxane
(PDMS)of the siloxane type. The porous Al2O3 green body was prepared
with an uniaxial pressing process. And then, SiO2 precusor was infiltrated
into the porous matrix under a vacuum chamber for the homogeneous
infilteration of precusor into the all pores of matrix. The SiO2 precusorinfiltrated
matrix was dried at 80 °C for 1 h, and then heat treated at 1600
°C for 1 h. During the drying process, PDMS does not undergo a sol-gel
reaction, whereas the TEOS is converted into glass-phased SiO2 by a sol-gel
reaction. It means that the siloxane type has higher conversion ratio of
precursor into SiO2 than the silicate type. The microstructure and
mechanical properties of prepared composites were evaluated using various
analytic techniques. Mullite (3Al2O3· 2SiO2) phase was observed at the
grain boundary between Al2O3 and SiO2, inducing the improvement of
mechanical properties of matrix. Therefore, the Al2O3–SiO2 composites
show higher mechanical properties in flexure strength and hardness than the
porous Al2O3 matrix. In addition, the mechanical properties of composite
prepared using PDMS were higher than those of composite prepared using
TEOS, caused by the enhancement of glassification by the increase in
conversion ratio of SiO2 precursor, in the absence of a sol-gel reaction.
Consequently, bi-phase composites with reasonable properties have been
successfully prepared through the IPN method using SiO2 precursors.
4:30pm E2-2-10 Probing the origin and evolution of strength in small
volumes with in situ TEM nanomechanical testing, A. Minor
(aminor@berkeley.edu), University of California, Berkeley; National
Center for Electron Microscopy, Lawrence Berkeley National Laboratory,
US INVITED
Recent progress in both in situ and ex situ small-scale mechanical testing
methods has greatly improved our understanding of mechanical size effects
in volumes from a few nanometers to a few microns. Besides the important
results related to the effect of size on the strength of small structures, the
ability to systematically measure the mechanical properties of small
volumes through mechanical probing allows us to test samples that cannot
easily be processed in bulk form, such as a thin film, a specific grain
boundary or a single crystal. This talk will describe our recent results from
in situ compression and tensile testing of metals with different starting
defect densities and sizes to illuminate the origin of size-dependent yield
strength behavior and fundamental deformation structures in nanoscale
samples.
91 Thursday Afternoon, April 26, 2012