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The determination of residual stresses in coatings generally goes with the
simultaneous determination of their elasticity constants. The main experimental
methods used for that purpose are briefly reviewed and their advantages and limitations
discussed: mechanical tests on self-bearing layers or on coated substrates,
indirect physical methods.
The dynamical resonant technique in free bending mode used for the determination
of constants of elasticity has been developed in view to characterize coated materials.
It has first been applied to homogeneous single coatings from room temperature up to
1,100°C for thicknesses varying from 2 to 200 μm with the help of a formalism
of composite beam. This formalism has then been extended analytically to three
and four layers in order to characterize multicoated materials. For thermochemical
treatments presenting a gradient of mechanical properties, a simplified n-layer model
allows to estimate the modulus gradient as a function of depth.
We have developed an original method allowing to determine the elasticity
constants of thin crystalline films deposited on substrates, which combines X-ray
diffraction and in situ tensile testing. This technique has been successfully
applied to measure the Poisson's ratio in tungsten thin films (150 nm) and molybdenum
sublayers (8 nm) of a Mo/Ni multilayer. This paper gives the principles and
experimental requirements for the Young's modulus determination.
Brillouin light scattering has been used to investigate the elasticity
properties of polycrystalline smooth fine-grained diamond films having various
diamond qualities. They have been deposited on titanium alloy Ti-6Al-4V by a
two-step microwave plasma-assisted chemical vapour deposition process
at 600°C. Taking advantage from the detection of a number of different
acoustic modes, a complete elasticity characterization of the films
has been achieved.
This paper describes a simple and efficient method to identify Young's modulus
of thermally sprayed coatings. The mechanical method is based on the cantilever
beam test, without the use of a strain gauge, combined with a finite element
numerical modelling and optimization technique. The influence of coating roughness
was taken into account in this work. Several types of coatings were tested and
their Young's moduli were calculated. A sensibility analysis was also performed.
Transmission and reflection measurements using synchrotron radiation have
been performed on a Ni sample submitted to tensile stress. For each studied crystalline
plane, the strain was determined from spectral analysis of the diffracted beam,
with a precision in the range of goniometric X-ray analysis. Apparent elasticity
characteristics were then deduced assuming plane stress state on the surface and
plane strain state in the bulk. The high elasticity modulus at the surface compared
with the bulk one could be explained by a roughness effect or a lower yield stress
near the surface.
This article studies the creep behaviour of the Ni/NiO system at 550°C
under oxygen. Several phenomena of damage appear during the deformation in creep.
These damages are in situ highlighted and separated with the help of the acoustic
emission technique. These results are post-mortem confirmed by various standard
techniques. Possible effects of interaction between the mechanisms of deformation
and the degradation behaviour were also examined.
Precipitation hardening in lead-cadmium-calcium alloys is a two stage process:
the first stage is a discontinuous hardening transformation without precipitation,
the second stage is a discontinuous lamellar precipitation of Pb3Ca. In order to
increase the mechanical and electrochemical properties of these alloys, we have studied
the influence of minor additions of tin on the precipitation hardening behaviour
of PbCaCd alloys, as this element is used to improve the electrochemical properties
of positive battery grids. The objective was to investigate in a systematic manner
the ageing and overageing behaviour of PbCdCaSn alloys in the case of two different
structural states: as-cast condition, rehomogenized state.
The pencil edging diamond wheels used for lateral automotive
glass grinding are composed of a mixture of metal powders (bond) and dispersed
super-abrasive diamond grits (having a 100 μm average size). The metallic bond
consists of a ductile alloy (sintered Ag+Cu+Ti powder mixture) and a hard skeleton
(W and cast iron). The principal characteristics expected are a good wear resistance as
well as a good cutting quality. In order to reproduce the industrial thermal cycle
of the sintering manufacturing process in a traditional furnace, this cycle was
simulated by dilatometric tests on green pellets of simplified metal powder mixtures.
The aim was to determine the sintering behaviour of each component of the
p-methoxy benzylidene malonitrile (MN1) and p-hydroxy benzylidene
malonitrile (MN2) were synthesized and tested as inhibitors for the corrosion
of mild steel in molar HCl. We have found that both of them inhibit the corrosion.
The maximum inhibition efficiency reached 100% for MN1 at 10-4 M and for
MN2 at 10-3 M. Current-voltage curves indicated that malonitriles act as mixed
type inhibitors. Their adsorption on the steel surface obeys to the Langmuir
isotherm model. The effect of temperature on the corrosion behaviour of steel
indicated that the inhibition efficiency of the two inhibitors decreases slightly
with the rise of temperature in the range 298-338 K. The apparent activation energies
for steel dissolution are greater than in the absence of inhibitors, which is
consistent with a chimisorption mechanism.
Four different techniques have been used to study the thermal cycling
effects on equiatomic Ti-Ni: Differential Scanning Calorimetry (DSC), Electrical
Resistance measurements (ER), Internal Friction measurements (IF) and Vickers
microhardness tests performed at room temperature. The measurements have been
performed on well annealed samples, samples cold worked at room temperature
and cold worked samples annealed at moderate temperatures.