bluuebunny/crossref_metadata_2025 huggingface dataset:
Aluminide Coating Formation on Internal Passages of GTD-111 Superalloy by Slurry Technique
Authors: Shirvani K. , Firouzi A.
Published: March 2009

The diffusion aluminide coatings are widely used in the air-cooling passages to protect
their surfaces against high temperature corrosion. In this study plain and Si-modified aluminide
coatings were applied by slurry technique on internal surfaces of Ni-base GTD-111 superalloy
cylindrical specimens derived from a gas turbine air-cooled blade. The slurries containing Al or Al
plus Si powders were applied on internal surfaces by injection method. Then, the samples were
heated to high temperature (800-1000°C) to form the coatings. Optical, SEM-EDS, and XRD were
utilized for characterizing microstructures and phase compositions of the coatings. The thicknesses
of applied coatings on internal surfaces were in the range of 30-50 μm that meets specifications for
diffusion coatings in such application (i.e. 25-756m). The examinations demonstrated that both
coating types were contained β-NiAl phase as the matrix. The uniformities of coatings applied on
different surface positions of passageway were determined. In addition, the effects of time and
temperature of coating process as well as mass of dried slurry on the coating thickness were also
discussed.
Depth Distribution of Residual Stress in Graded (Ti, Al) N Coating and Fatigue Properties of Coated Stainless Steel
Authors: Xin Li , Liu Ping , Zhao Hui , Zhu Sheng Long , Wang Fu Hui
Published: March 2009

The depth distribution of the residual stress in graded (Ti, Al) N coating deposited on steel
by arc ion plating was measured by the Stripping Layer Substrate Curvature Technique, and the effect
of graded (Ti, Al) N and mono-layered (Ti, Al)N coating on the fatigue properties of
1Cr11Ni2W2MoV stainless steel were investigated. The depth distribution of the residual stress in
mono-layered Ti70Al30N and TiN were also measured for comparison. The results show that the
residual stresses in the coatings are compressive, which increase gradually from the coating/substrate
interface and reach a maximum value at the middle region, then decrease until the surface. Compared
with TiN and Ti70Al30N, the stress maximum value in the graded coating is nearer to the coating
surface. It is also shown that the fatigue strength of the graded (Ti, Al)N and Ti70Al30N coated
samples are superior to that of the uncoated substrate. The improvement of the fatigue properties for
the coated samples is thought to be attributed to the hard coatings with high compressive stress.
Fireside Corrosion in Energy Recovery Boilers and Maintenance Issues
Authors: Brossard Jean Michel , Nicol François , Chaucherie Xavier
Published: March 2009

Fireside corrosion is since a long time the main limitation to increase efficiency of energy
recovery boilers of waste to energy (W-t-E) facilities. Nevertheless, the increase of steam
conditions in addition with the variation of feeding fuels composition imply greater risks of fouling
and corrosion along with heat exchanger failure, loss of plant availability and high maintenance
costs. Fireside corrosion mechanisms had already been widely treated in the literature and this paper
will review the main critical factors that enhance fireside corrosion of superheater. Recent failure
cases will be developed in regards with recent studies that provide interesting routes to predict
corrosion failure and develop maintenance strategy.
Study of Oxyhydroxides Formation on P92 Steel on Al-CVD Coating in Contact with Ar+20% H2O at 650°C by TG-Mass Spectrometry
Authors: Castañeda S.I. , Bolívar F.J. , Pérez F.J.
Published: March 2009

Volatile species released during the initial stages of oxidation of a P92 ferritic steel, with
and without an aluminized coating, at 650°C in Ar+20%H2O for 150h were studied. TG-MS
experiments were conducted in a closed steam loop in order to obtain information about the
oxyhydroxides formation as reaction between coatings and steam. From those results, the role of the
different coating element could be established and optimized for the coating durability. An
oxidation mechanism based on the TG-MS results is given. The morphology/composition and
structure of the oxidized samples were also studied using SEM/EDS and XRD techniques.
Al-Mn CVD-FBR Protective for Steam Corrosion Applications
Authors: N'Dah Eugene , Bolívar F.J. , Sánchez L. , Hierro M.P. , Tsipas Sofia , Pérez F.J.
Published: March 2009

Ferritic steels are usually used in boiler or supercritical steam turbines which operate at
temperatures between 600-650°C under pressure. Protective coatings are often applied in order to
increase their oxidation resistance and protect them against degradation. In this study new Al-Mn
protective coatings were deposited by CVD-FBR on P92 ferritic steel. The initial process
parameters were optimized by thermodynamic calculations using Thermo-Calc software. Then,
those parameters were used in the experimental procedure to obtain Al-Mn coatings at low
temperature and atmospheric pressure. Co-deposition was achieved at moderate temperatures in
order to maintain the substrates` mechanical properties. The coatings` microstructure and phase
constitution was characterized. Fe-Al intermetallic coatings containing Cr and Mn were obtained.
The phase constitution is discussed with reference to the Fe-Al-Mn ternary phase diagram. The
effect of diffusion heat treatment on the phase transformations as well as the steam oxidation
resistance of these coatings at 650°C and 800°C was investigated.
Evaluation of Al-Hf Coating on Ferritic Steels by CVD-FBR Technology in Steam Oxidation
Authors: Bolívar F.J. , Sánchez L. , Hierro M.P. , Trilleros J.A. , Pérez F.J.
Published: March 2009

The steels with chromium contents between 9 and 12%wt are used for power plants with
advanced steam conditions. These steels possess good creep properties similar to the 9% Cr steels
as well as good creep and good oxidation resistance at temperatures between 500-600°C. In the last
years efforts have been made to develop coatings for protection against oxidation in order to allow
operation of steam turbines at 650°C. In this study, Al-Hf protective coatings were deposited by
CVD-FBR on the ferritic steel HCM-12A followed by a diffusion heat treatment, and were shown
to be protective at 650°C under steam for at least 3000 hours of laboratory steam exposure under
atmospheric pressure. The morphology and composition of the coatings were characterized by
techniques, including scanning electron microscopy (SEM), electron probe microanalysis, and Xray
diffraction (XRD). The results showed a substantial increase of steam oxidation protection
afforded by Al-Hf coating deposited by the CVD-FBR process.
Development of Strain in Oxides Grown in Steam Tubes
Authors: Wright Ian G. , Sabau Adrian S. , Dooley R.B.
Published: March 2009

In this study, the foundation is being developed for the numerical simulation of the
processes that determine the oxide scale exfoliation behavior of the steam-side surfaces of
superheater and reheater tubes in a steam boiler. Initially, the assumptions concerning the base state
for calculating oxide strains also were critically examined. The state of stress-strain of an oxide
growing on the inside surface of an externally-heated tube was considered for the conditions
experienced in a boiler during transition from full- to partial-load operation. Since the rate at which
the oxide grows is an important consideration, it was necessary to determine the appropriate
temperature to use in the oxidation rate calculations. The existence of a temperature gradient
through the tube, and the cyclic nature of the boiler operation (temperature and pressure) were
considered; the growth temperature of the oxide was taken to be the oxide surface temperature. It
was determined that the commonly-used approach for accounting for geometrical effects when
calculating stress-strain development in a growing oxide scale of using the analogy of an infinitelylong
flat plate gave sufficiently different results than when using a cylindrical geometry, that the
latter was adopted as the preferred calculation procedure. Preliminary calculation of strains
developed in multilayered oxides formed on alloy T22 as a function of boiler operating conditions
indicated the magnitude of the strains in each layer; the large strain gradients between the layers
inferred the importance of the detailed scale morphology in determining the mode of exfoliation.
Slag-Refractory Interaction in Slagging Coal Gasifiers
Authors: Matyas Josef , Sundaram S.K. , Hicks B.J. , Edmondson Autumn B. , Arrigoni Benjamin M.
Published: March 2009

The combustion chamber of slagging coal gasifiers is lined with refractories to protect
the steel shell of the gasifier from elevated temperatures and corrosive attack of the coal slag.
Refractories composed primarily of Cr2O3 have been found most resistant to slag corrosion, but
they continue to fail performance requirements. Post-mortem analysis of high-chromia refractory
bricks collected from commercial gasifiers suggests that slag penetration and subsequent spalling of
refractory are the cause of the short service life of gasifier refractories [1]. Laboratory tests were
conducted to determine the penetration depth of three slags representative of a wide variety of coals
in the United States into chromia-alumina and two high-chromia refractories. Variables tested were
refractory-slag combinations and two partial pressures of O2. Slag penetration depths were
measured from spliced images of each refractory. Samples heated to 1470°C for 2 hrs had
maximum penetration depths ranging from 1.99±0.15 mm to at least 21.6 mm. Aurex 95P, a highchromia
refractory containing 3.3% phosphorous pentoxide (P2O5), showed the least slag
penetration of all refractories tested. P2O5 likely reacts with CaO and MgO in the slag, forming an
immiscible Ca-Mg phosphate phase. The extraction of basic components from slag causes an
increase in slag viscosity restricting the molten slag penetration into the refractory.
Modelling of Corrosion Induced Stresses during Zircaloy-4 Oxidation in Air
Authors: Busser Vincent , Desquines Jean , Fouquet Stéphanie , Baietto Marie Christine , Mardon Jean Paul
Published: March 2009

In the frame of its research work on nuclear fuel safety, the French “Institut de
Radioprotection et de Sûreté Nucléaire” (IRSN) has highlighted the importance of cladding tube
oxidation on its thermomechanical behavior. The occurrence of radial cracking and spallation has
been observed as the main mechanisms for the zirconia layer degradation during transient
experiments. A study of these two mechanisms has been jointly launched by IRSN and Areva-NP.
Thus laboratory air oxidations of fully recrystallized or stress-relieved low-tin Zircaloy-4 cladding
tubes have been performed. Representative oxide layer thicknesses varying from 10 to 100 0m have
been obtained. SEM micrographs of the obtained oxidised samples show that short circumferential
cracks are periodically distributed in the oxide thickness. For specimens with oxide film thickness
greater than 30 0m, radial cracks are initiated from the outer surface of the oxide layer and
propagated radially. Veins characterised by the lack of circumferentially orientated crack are
evidenced. All these phenomena are mainly linked to high compressive stress levels in the zirconia
layer.
A model describing the stress evolution in the oxide and in the cladding has been developed. This
model takes into account the influence of elasticity, cladding creep, oxide growth and thermal
expansion. Deflection tests data [15] are used to calibrate the oxide growth modelling. The model
enables the evaluation of strain or stress profile in the oxide layer and in the base metal. Numerical
results are in good agreement with a large set of axial and circumferential strains measurements.
Further a better understanding of cracking mechanisms is achieved considering the good agreement
between experimental and numerical analysis.
Comparison of the High Temperature Surface Reactivity in Impure Helium of Two Materials for Gas Cooled Reactors
Authors: Cabet Céline , Girardin Gouenou , Rouillard Fabien , Chapovaloff Jerome , Wolski Krzysztof , Pijolat Michèle
Published: March 2009

Nickel base alloys Haynes 230 and Inconel 617 are of interest for gas cooled reactors. At
high temperature in impure helium, they generally form surface chromium-rich oxides. However
above a critical temperature called TA, the scales are not stable anymore and the chromia
destruction comes with a production of carbon monoxide. Reactivity tests on model alloys, with and
without carbon, prove that chromia is reduced by the carbon from the alloy. TA vs P(CO) curves
were also plotted for the two commercial alloys based on the experimental determination of TA in
various atmospheres with increasing partial pressures of carbon monoxide. Unexpectedly, both
materials exhibit an almost identical behavior although a basic equilibrium approach suggests that
the chromia scale would be reduced in different conditions due to the thermodynamic particularity
of the interfacial alloy/scale system.
Kinetic Study of the Low Temperature Internal Oxidation of Nickel Based Model Alloys Exposed to PWR Primary Water
Authors: Ter-Ovanessian Benoît , Deleume Julien , Cloué Jean Marc , Andrieu Eric
Published: March 2009

Two Ni-Fe-Cr ternary alloys have been oxidized in simulated pressurized water reactor
primary water at 360°C for 1000 h. The chemical composition of those alloys were chosen in order
to be representative of the one of chromium depleted areas under the oxide scale of industrial alloys
(e.g. alloy 600) exposed in the same conditions. The resulting oxidized structures (corrosion scale
and underlying metal) were characterized using complementary analytical methods (FEG-SEM,
TEM, SIMS, optical microscopy). On the one hand, the characterized external oxide layer is very
close to the one observed on industrial nickel-base alloys, hence validating the use of such model
alloys. On the other hand, both free oxygen and oxides have been detected at grain boundaries
several micrometers under the metal/oxide interface. Implications of such a finding on the involved
transport mechanisms for oxygen and the intergranular stress corrosion cracking resistance of
nickel-base alloys are then discussed.
Oxide Layers Mechanical Properties for Ni Base Alloys in HTR Environment
Authors: Kaczorowski Damien , Girardin Gouenou , Chamousset S.
Published: March 2009

Nickel base alloys 617 and 230 are promising candidates for the Intermediate Heat
eXchanger (IHX) of GenIV Very High Temperature gas cooled Reactors. The capability to maintain
an oxide layer as an efficient barrier against corrosion under mechanical loading is investigated
through SEM in situ tensile test. The mechanical properties of external oxide layers are so compared
between the two alloys. Cracks and spallation are observed. Few differences could be observed
between these two alloys when pre oxidized in impure helium.
New Experimental Loops for Research Reactor LVR-15
Authors: Růžičková M. , Hájek P. , Všolák R. , Berka J. , Šmejkalová J.
Published: March 2009

Two experimental loops for operation in research reactor LVR-15 in ÚJV Řež are
recently under preparation: High Temperature Helium Loop (HTHL) and SuperCritical Water Loop
(SCWL). Pure helium will be used as working medium in HTHL and its main physical parameters
are: operating pressure 7MPa, max. temperature in the test section 900°C and flow rate 36kg/h.
HTHL will include helium purification system, system for dosage of impurities (e.g. CO2, H2, H2O,
O2, N2 etc.) and helium sampling. Helium purification experiments and testing of materials in
simulated HTR conditions will take place in HTHL in the future. Main parameters of the SCWL are
25MPa, max. temperature in the test section 600°C, flow rate max. 200kg/h. SCWL will be used for
corrosion tests of candidate materials, studies of water radiolysis at supercritical conditions and for
testing of water chemistry suitable for operation. Both loops possess an irradiation channel with
quite complicated internals design, whose complexity is imposed by current constraints on
constructional materials of nuclear experimental devices, which limit the choice and maximum
surface temperature of material of construction to 500°C for austenitic stainless steel. The working
temperature will thus be attained only in a restricted volume of the test section. The channel
internals will be briefly described. The mentioned loops will represent novel experimental devices,
whose objective is to gain and extend knowledge on materials and environment performance under
the influence of radiation.
Corrosion of MA754 and MA956 in a Commercial Aluminum Melter
Authors: Hurley John P. , Kelley Carl , Bornstein Norman , Wright Ian G.
Published: March 2009

The University of North Dakota Energy & Environmental Research Center is working
with Oak Ridge National Laboratory to test two oxide dispersion-strengthened alloys that could be
used to construct very high-temperature heat recuperators for the aluminum-melting industry. For
the initial tests, uncooled rings of MA754 and MA956 piping were exposed for 5½ months to gases
leaving an aluminum melter furnace at 1200°–1290°C. The MA956 suffered spotty areas of severe
corrosion and lost 25% of its weight. Scanning electron microscopy showed that there were small
spots of alkali-rich corrosion products on the alloy surfaces, indicating the impact of droplets of
fluxing agents. The corrosion products in these areas were mixed Fe, Cr, and Al oxides, which were
depleted in Cr near the gas surface. However, Al concentrations in the remaining metal were
typically between 3.5% and 4.0%, so there was a sufficient reservoir of Al remaining in the alloy to
prevent simple breakaway corrosion which could have occurred if the Al were significantly
depleted.
The MA754 lost approximately 15% of its weight and showed void formation within 2 mm of the
gas–metal surfaces. Within the porous area, the Cr had largely segregated into oxide precipitates up
to 50 9m in diameter, leaving the remaining metal Ni-rich. Below the porous layer, the alloy
composition was relatively unchanged. Remains of Na- and Al-rich particles that had impacted the
surface sporadically were visible but had not obviously affected the surface scale as they had with
the MA956.
The Oxidation Behaviour of Pack-Treated Heavy Refractory Alloys
Authors: Martinz Hans Peter , Tourneret Bruno , Jehanno Pascal , Nigg Brigitte
Published: March 2009

The heavy refractory metals and alloys Molybdenum (Mo), Molybdenum – Silicon –
Boron (Mo–Si-B; “MoSiBor”), Tungsten (W), Tungsten – Copper (W-Cu), Tungsten – Nickel –
Iron (W-Ni-Fe; “Densimet D 176 and 185”) and Tungsten – Nickel – Molybdenum - Iron (W-Ni-
Mo-Fe; “Densimet D2M”) were pack-treated at 1100°C with Silicon - powder to form siliconized
zones and/or intermetallic phases which are intended to be more oxidation resistant than the plain
base materials.
These materials (especially the W-based ones) are used at ambient conditions as counterweights,
radiation shields etc. because of their high density as well as at high temperatures (600 – 900°C) as
metal forming tools, electrodes etc. because of their refractory metal content. In both areas of
conditions oxidation of the plain materials occurs and leads to lower functionality or destruction.
A suitable oxidation test has been defined to check the presumably enhanced oxidation resistance of
the pack-treated materials: an isothermal high temperature oxidation test at 700 and 900°C for one
week. At these conditions all untreated materials would have been more or less strongly oxidized.
Improved oxidation resistance could be found for the materials with pack-cementation treatment
except for sintered Tungsten (92% dense), sharp etched D 185 and D 176 at 900°C and Tungsten –
Copper at both temperatures. More stable and dense superficial oxides were formed which led to
decreased oxidation rates and could help to increase functional stability and the lifetime of the
components. Different pack-treatments e.g. with chromium or silicon plus chromium could improve
the behaviour of the materials which failed within this work.
Characterization and Failure Analysis of Incoloy 800 Used as Thermowell Subjected to High Temperature Erosion-Corrosion
Authors: Promdirek P. , Chandra-Ambhorn Somrerk , Tongtae C. , Anantawirun C. , Buaphuen C.
Published: March 2009

In the present study, a thermowell made of Incoloy 800 (33Ni-21Cr-46Fe) was used as a
part to cover and therefore to protect a thermocouple inserted in a tube used in petrochemical
process. It was then subjected to the atmosphere in the tube containing moving carbon particles at
900°C. One of the critical failure types observed was the combination of both solid particle erosion
and oxidation. Thermowell degradation, which accounted for the corrosion-affected-erosion of
materials, was significantly observed in the area where impingement at the head surface area of
thermowell. The physicochemical characterization revealed that the thermowell consisted of two
layers. The inner one is the incoloy 800 base metal, whereas the outer layer was clad with a cobalt
base superalloy. Kinetic of oxidation of both materials in each layer, which was performed in air at
1173K presented the different parabolic rate. Metal oxide and surface morphology of thermowell,
which was investigated in the simulated condition, were then examined by XRD, OM and SEM. A
finite element software was furthermore applied to simulate the flow direction and the velocity of
the particles. It was found that the maximum speed of particles (180 m s-1) was at the surface where
the impingement angle of particle is 90°. Comparing to the failure of themowell in service, it was
concluded that the failure of thermowell depends primarily on the impingement angle of particle.
Design of the shape of thermowell, as well as the cladding with the higher erosion-corrosion
resistance materials, were recommended to be carried out to improve the erosion-corrosion
resistance of this part.
On the Effect of Surface Treatment to Improve Oxidation Resistance and Conductivity of Metallic Interconnects for SOFC in Operating Conditions
Authors: Fontana S. , Vuksa M. , Chevalier Sébastien , Caboche G. , Piccardo P.
Published: March 2009

Due to the reduction of operating temperature from 1000°C to 800°C, chromia forming
alloys are the best candidates for interconnects in Solid Oxide Fuel Cells (SOFCs). These
interconnects have to be operational in service conditions, at 800°C in air (cathode side) and in
humidified hydrogen (anode side). The performance of the interconnect stainless steels is limited by
the oxide scale formation (chromia), the low electronic conductivity of this scale and the possible
volatility of chromium oxides. In the field of high temperature oxidation of metals, it is well known
that the addition of a nanometric layer made of reactive element oxide such as, La2O3, Nd2O3 and
Y2O3 by MOCVD (Metal Organic Chemical Vapor Deposition) on alloy surface resulted in an
important improvement in the high temperature oxidation resistance. These coatings are made on
metallic alloys in order to form perovskite oxides such as LaCrO3, NdCrO3 and YCrO3, which are
expected to present a good conductivity at 800°C in air. However, this temperature looks somewhat
too low to guarantee the formation of perovskite oxides and thus to improve the oxidation resistance
and electrical conductivity. In fact, XRD analyses revealed that for Y2O3 coatings, perovskite
oxides were not formed after oxidation in air at 800°C for 100 hours. The goal of this study is to
perform pre-oxidation at 1000°C for 2 hours in air under atmospheric pressure on coated
Crofer22APU to pre-form perovskite phases. The so-prepared perovskite were tested in a
thermobalance in air. Experiments performed in H2/10%H2O under 150 mbar at 800°C validated
the coating influence from the anode side as well as the cathode side. The corrosion products were
analyzed after 100 hours ageing at 800°C by SEM, EDX, and XRD. ASR (Area Specific
Resistance) was measured for the same times and temperature in air.
Multifunction High Temperature Coating System Based on Aluminium Particle Technology
Authors: Kolarik Vladislav , Juez-Lorenzo Maria , Anchústegui M. , Fietzek Harald
Published: March 2009

Spherical Al particles sized in the range of 2 to 5 μm were deposited with an organic
binder by brushing on the austenitic steel X6 CrNi 18-10 (Alloy 304H). The coated samples were
annealed in air at 400°C for 1 h in order to expel the binder. For studying the oxidation behaviour in
air, isothermal experiments were performed at 700°C and 900°C with oxidation times of 5 h, 100 h
and 1000 h. The oxide formation was studied in situ by high temperature X-ray diffraction (HTXRD)
up to 100 h. Field emission scanning electron microscopy (FE-SEM) was applied to investigate
the surface and the cross-section of the particle coating.
During oxidation, the stable α-Al2O3 was identified in situ by HT-XRD on all studied samples at
both temperatures. No meta-stable alumina phases were found. In the initial state, 2 h at 900°C, the
Al particles are completely oxidised to hollow alumina spheres, controlled predominantly by the
reaction due to the small particle size and relatively high surface portion. Simultaneously, the Alrich
diffusion layer is formed in the substrate. On further exposure, a thin protective alumina scale
continues growing on the top of the diffusion layer. After exposure to both 700°C and 900°C, a
coating structure was encountered, which consists of a quasi-foam top coat from conjoint hollow
spherical alumina particles and an Al-rich diffusion layer below. The quasi-foam top coat has the
potential to effectuate as thermal barrier by gas phase insulation, while the diffusion layer below
serves as protective coating against oxidation.
The approach by particle size processing opens a potential for obtaining a complete thermal barrier
coating system in one manufacturing step. The coating properties can be adjusted by parameters
like selection of source metal/alloy, particle size, substrate, binder and heat treatment.
Investigation of Oxide-Nucleation on Ferritic FeCr Interconnect Alloys for Solid Oxide Fuel Cells Exposed to Anode and Cathode Gases at 850°C
Authors: Kunschert Georg , Martinz Hans Peter , Schütze Michael
Published: March 2009

In recent years solid-oxide fuel cell (SOFC) interconnect components have proven to be a
key-component accountable for the functionality of high temperature fuel cells. Amongst adequate
thermal expansion and high temperature strength, highest oxidation resistance in anode and cathode
gases under thermal cycling conditions is required in order to reach long term durability,
particularly when using thin film light-weight components with particular focus on automotive
applications. In order to match the challenging parameter profile Plansee developed the
mechanically alloyed ITM, a ferritic P/M Fe26Cr alloy strengthened with additions of Y2O3
dispersoids, since it has been observed that apart from their HT strengthening effect, which is of
specific interest for thin sheets components, finest ODS particles reduce the growth and enhance the
adhesion of the forming oxide layers. The latter effect is of particular interest in applications where
alloys are exposed to HT cyclic conditions.
In this work the nucleation phase of the oxide scale formation on P/M ODS Fe26Cr ITM is
compared to that on a reference ingot steel Fe22Cr in typical anode gases containing significant
amounts of H2, CO and approximately 3% H2O as well as in laboratory air at 850°C. Thermal
cycling oxidation tests following the COTEST standard up to 168h are carried out in both
environments. Moreover cyclic oxidation tests are performed in dry anode gas. Detailed studies of
oxide scale formation and evolution by means of electron microscopy of cross sections as well as
oxide surfaces are undertaken.
Oxidation and Corrosion Effects on Thermal Fatigue Behaviour of Hot Work Tool Steel X38CrMoV5 (AISI H11)
Authors: Lamesle P. , Salem Medhi , Le Roux Sabine , Dour Gilles , Aria Farhad Rezai
Published: March 2009

Effects of atmosphere and specimen geometry on thermal fatigue (TF) crack initiation
and propagation in a low Si content hot work tool steel X38CrMoV5-47HRC were investigated.
The TF specimen’s geometry enhances the uni-axial TF loading conditions. A high frequency
induction heating (3 to 4 MHz) is used. A new TF rig, working under air and/or inert atmosphere
with reduced PO2 has been set up. The reduction of PO2 results in localized oxidation sites. Whatever
geometry and atmosphere conditions, TF cracks initiate exclusively in the oxide layers. Damage
mechanisms are environment dependant. Under laboratory air, parallel macroscopic cracks initiate
perpendicular to the hoop stress. Under argon and nitrogen, SEM surface observations show that
initiated cracks coalesce by zigzagging along crystallographic paths between non-oxidized zones.
In-depth crack propagation mechanism is mainly trans-granular. TF crack initiation life under air
and in presence of Fe-Al intermetalllics is decreased in comparison to inert atmosphere.
Influence of Tantalum on the Rates of High Temperature Oxidation and Chromia Volatilization for Cast (Fe and/or Ni)-30Cr-0.4C Alloys
Authors: Berthod Patrice , Hamini Yassin , Aranda Lionel
Published: March 2009

Four cast superalloys, Fe-base and (Fe,Ni)-base alloys, all containing 30%Cr and 0.4%C,
were elaborated with addition of 3% and 6% of tantalum. Their oxidation behaviours were studied
at 1000, 1100 and 1200°C during 50 hours. The oxidized surfaces of the samples were
quantitatively characterized by measurements of thicknesses and surface fractions of internal
oxides. The thermogravimetry files were treated according to the {m×(dm/dt) = Kp - Kv×m}
equation, to obtain simultaneously the parabolic constant and the chromia volatilization constant.
The internal tantalum oxides are more present in the Fe-base alloys and the carbide-free zones are
less developed for the (Fe,Ni)-base alloys than for the others. The Fe-base alloys oxidize faster than
the (Fe,Ni)-base and Ni-base alloys. The comparison with the corresponding Ta-free ternary alloys
shows that the presence of Ta tends to accelerate the oxidation.
Study of the Behavior in Oxidation at High Temperature of Ni, Co and Fe-Base Alloys Containing Very High Fractions of Carbides
Authors: Berthod Patrice , Lemoine Pierric , Aranda Lionel
Published: March 2009

Nine cast alloys reinforced by very high fractions of carbides, Ni-30Cr-xC, Co-30Cr-xC
and Fe-30Cr-xC with x varying from 1.2 to 2.0, were tested in oxidation at high temperature
between 1,000 and 1,200°C in air for 50 hours. After oxidation, their surfaces and sub-surfaces
were characterized. Even for very high carbon contents, the chromia-forming behaviour of the
nickel alloys is kept. The oxidation modes of the cobalt alloys and iron alloys are not changed
compared to low carbon alloys of these families. The differences of diffusion easiness of chromium
in matrix, between nickel alloys, cobalt alloys and iron alloys are the same as for alloys with lower
carbon contents, as suggested by the lower chromium gradients in the nickel alloys compared to the
two other alloy types. Sub-surface microstructure transformations due to oxidation were observed in
some cases (coarsening of carbides due to an inwards diffusion of carbon, change of the sharing
between BCC-FCC of iron matrix due to outwards diffusion of chromium). Catastrophic oxidation
never occurred for these alloys during the 50 hours of exposition to air at high temperature.
High Resolution MicroRaman Study of Blisters in Cr2O3 Thermal Oxide Films
Authors: Kemdehoundja Mbaihoudou , Grosseau-Poussard Jean Luc , Dinhut J.F. , Bonnet G.
Published: March 2009

Using Raman microprobe spectroscopy made it possible to study the buckling phenomenon
in chromia films grown at 900°C in air from a Ni30at%Cr alloy. Blisters have been optically observed
to be circular and, from the top view, the mean radius has been measured with an accuracy of about
1%m. An autofocus device allows the characterisation of the profile of each blister and the shift of the
A1g Raman peak of chromia gave the local stress far from the blister and all along the buckled zone.
From these observations, the induced spalling has been related to the blister morphology.
Comments on the Quantification of Mechanical Adhesion Energy of Thermal Oxide Scale on Metallic Substrate Using Tensile Test
Authors: Chandra-Ambhorn Somrerk , Promdirek P. , Lothongkum Gobboon , Wouters Yves , Galerie Alain
Published: March 2009

The tensile test, accompanied by the corresponding theoretical model, has been
developed to quantify the mechanical adhesion energy of the oxide scale on metallic substrate in
our previous works. The method to quantify the adhesion energy took into account the effect of
residual stress. The effect of the variation of the measured residual stress on the quantified adhesion
energy is assessed in this paper. For the scales failed at strains initiating the spallation of 0.018 and
0.011 followed by the transverse crack, it was found that the quantified adhesion energy of the
oxide is not sensitive to the variation of the residual stress measured in the range from 0.5 to
2.0 GPa. This is due to the compensation of the decrease in stored energy due to the stress applied
in the loading direction (x direction) and the increase in stored energy due to the stress applied in
the direction perpendicular to the loading direction (y direction) when the residual stress increases.
For the scale failed by the transverse crack followed by the spallation, the quantified adhesion
energy tends to be sensitive to the variation of the measured residual stress. The assumption of
energy relaxation during the tensile test is alternatively proposed. It is assumed that the energy
stored due to the stress in x and y directions is totally released at the first crack. The energy stored
due to the stress in y direction from strain initiating the crack to strain initiating the spallation is
used in the quantification of the adhesion energy. The scatter of the adhesion energy values
quantified by this method and those measured by the inverted-blister test is reduced comparing to
the results reported in the previous work.
The Effects of Reactive Element Oxide Coatings on the High Temperature Oxidation of FeCrAl Alloy
Authors: Cueff Régis , Nguyen C.T. , Buscail Henri , Caudron Eric , Issartel Christophe , Riffard Frédéric
Published: March 2009

The effect of reactive element additions (external doping as an yttrium-oxide coating on
the metal) on the oxidation behaviour of a commercial FeCrAl alloy (Kanthal A1) has been
investigated during isothermal exposures in air at 1373K. The scale growth kinetics of the bare
alloy obey a parabolic rate law during the whole oxidation test whereas the kinetic curves of the
yttrium-bearing specimen exhibit an initial transient stage during the first hours, followed by a
parabolic regime. The yttrium addition to the bare alloy does not give the beneficial effect usually
ascribed to the reactive elements. No significant oxidation rate improvement of the alloy is
observed, the parabolic rate constants values obtained are roughly similar for the both specimens. In
situ X-ray diffraction reveals a marked influence of the reactive element on the composition of the
oxide scale. The oxide layer formed on the yttrium-bearing specimen revealed, in addition to α-
alumina which is the main oxide also identified on the bare specimen, the presence of yttrium
aluminates (YAlO3, Y3Al5O12) located in the outermost part of the layer.
Influence of Interstitials Content on the Sensitivity of Alloy 718 to Oxidation Assisted Intergranular Fracture
Authors: Ter-Ovanessian Benoît , Deleume Julien , Cloué Jean Marc , Andrieu Eric
Published: March 2009

Alloy 718 is known to be sensitive to oxidation assisted intergranular cracking. It is also
demonstrated that the occurrence of jerky flow (also called Portevin-Le Châtelier effect) stops the
intergranular damaging mechanism. As dynamic strain ageing is known to be linked with the alloy
content of interstitial species, the aim of the present work is to study the effect of carbon, nitrogen
and oxygen concentrations on the mechanical behaviour of thin tensile specimens tested under
oxidation conditions close to those encountered industrially for turbo machine disks. Thanks to heat
treatments performed under reducing atmosphere, the content of interstitial species in tested alloy
718 samples is gradually curbed. Tensile specimens were then tested between 550 and 700°C for
the strain rate range [10-5, 10-1] s-1. The key point of this work is that, for a given testing
temperature, the tensile tests clearly demonstrated that the transition from an intergranular fragile
fracture mode to a transgranular ductile one was always linked with the occurrence of Portevin-Le
Châtelier phenomenon but for slower strain rates in comparison with what was observed on the as
received aged material tested in the same conditions. This shift of the transition of fracture mode
through the lower strain rates remained true until a threshold value of the heat treatment time under
reducing atmosphere. Specimens heat treated over this value systematically exhibited a fully
transgranular ductile fracture mode, whatever the plastic flow regime was. Implication of such a
finding on the intergranular embrittlement of alloy 718 by high temperature oxidation is then
discussed.
Oxidation Behavior of Mo Containing Alloys
Authors: Dokumacı Esra , Önay Bulent
Published: March 2009

In this study, high temperature (T>500oC) oxidation behavior of two commercial Ni-base
alloys and two experimental alloys, all containing more than 10% Molybdenum, is investigated.
Experimental alloys were prepared from high purity materials using an arc-melting furnace under a
protective environment. During tests, samples were exposed to the stagnant air environment of a
high temperature furnace for predetermined times. Extent of oxidation was determined from sample
mass change measurements as well as morphological and chemical analyses of the oxidation
products. For analyses, a scanning electron microscope (SEM) equipped with backscattered electron
(BE) and energy dispersive spectroscopic (EDS) detectors was used. Crystalline phases formed in
the product scales over the alloy samples were identified by an x-ray diffractometer (XRD).
Preliminary results indicate that although Mo in the alloy prevents the development of a protective
oxide scale at the alloy surface, presence of alloying elements such as Cr or Al can decrease this
negative effect of Mo on oxide scale formation.
Direct Measurements of the Chromium Activity in Complex Nickel Base Alloys by High Temperature Mass Spectrometry
Authors: Gossé Stéphane , Alpettaz Thierry , Rouillard Fabien , Chatain Sylvie , Guéneau Christine , Cabet Céline
Published: March 2009

Chromium rich, nickel based alloys Haynes 230 and Inconel 617 are candidate materials
for the primary circuit and intermediate heat exchangers (IHX) of (Very)-High Temperature
Reactors. The corrosion resistance of these alloys is strongly related to the reactivity of chromium
in the reactor specific environment (high temperature, impure helium).
At intermediate temperature – 900°C for Haynes 230 and 850°C for Inconel 617 – the alloys under
investigation are likely to develop a chromium-rich surface oxide scale. This layer protects from the
exchanges with the surrounding medium and thus prevents against intensive corrosion processes.
However at higher temperatures, it was shown that the surface chromia can be reduced by reaction
with the carbon from the alloy [1] and the bare material can quickly corrode. Chromium appears to
be a key element in this surface scale reactivity. Then, quantitative assessment of the surface
requires an accurate knowledge of the chromium activity in the temperature range close to the
operating conditions (T ≈ 1273 K).
High temperature mass spectrometry (HTMS) coupled to multiple effusion Knudsen cells was
successfully used to measure the chromium activity in Inconel 617 and Haynes 230 in the 1423-
1548 K temperature range. Appropriate adjustments of the experimental parameters and in-situ
calibration toward pure chromium allow to reach accuracy better than ± 5%.
For both alloys, the chromium activities are determined. Our experimental results on Inconel 617
are in disagreement with the data published by Hilpert [2]. Possible explanations for the significant
discrepancy are discussed.
Thermal Barrier Coatings on Nickel Superalloy Substrates
Authors: Zhao X. , Xiao Ping
Published: March 2009

Thermal barrier coatings (TBCs), which comprise metallic and ceramic multilayers, have been widely used in the hot section of aeroturbine engines to increase turbine efficiency and to extend the life of metallic components. An improvement in TBCs requires a better understanding of the complex changes in their structure and properties that occur under harsh operating conditions that eventually lead to their failure. In this paper, the developments of TBCs over the past 30 years are briefly reviewed. A description of materials issues involved in the state-of-art and next generation TBCs systems is presented, together with a summary of the current understanding of failure mechanisms; highlighting the challenges and prospects in TBCs research.
Positronium Chemistry in Polymeric Membrane Systems
Authors: Jean Yan Ching , Chen Hong Min , Lee L. James , Yang Jin Tao , Gu Xiao Hong , Hung Wei Song , Lee Kueir Rarn , Lai Juin Yih , Sun Yi Ming , Hu Chien Chieh
Published: March 2009

Positron and Positronium chemistry has been pursued and advanced by many scientists and engineers in both fundamental understanding of Positronium atom and its applications to chemical and polymeric systems during the last decade. This paper presents our recent results from collaborative investigations of positron annihilation in polymeric membranes. Future perspectives of applying Positronium chemistry to membrane science and technology and other related disciplines of nanotechnology, chemical engineering, materials science, energy research, molecules with positrons, biological and medical sciences appear to be promising.
Disordered Structures of Adsorbed Hydrogens on Ni(111) Surface Studied by Slow Positron Beam and LEED
Authors: Komagata S. , Hirota K. , Arii S. , Honda S. , Takaishi H. , Kanazawa Ikuzo , Fukutani K. , Nozawa K. , Komori F.
Published: March 2009

The positron annihilation γ-ray spectra emitted from hydrogen-adsorbed Ni(111) surface in some conditions were measured. We have discussed the disordered structures of adsorbed-hydrogens on Ni(111) through analyzing the positron annihilation spectra.
Vacancy-Hydrogen Complexes in ZnO
Authors: Kuriplach Jan , Brauer Gerhard , Melikhova Oksana , Čížek Jakub , Procházka Ivan , Anwand W. , Skorupa Wolfgang
Published: March 2009

Hydrogen is an important impurity in zinc oxide and can be incorporated into the lattice in several ways. Hydrogen can be also bound by vacancies that can be studied using positron annihilation techniques. Here we examine theoretically oxygen and zinc vacancies in ZnO, the latter also with hydrogen atoms inside. Several computational approaches are employed to determine the defect geometries and related positron characteristics. Positron-induced forces are also taken into account. Calculated positron lifetimes are compared with those observed in experiment, which gives an indication of the presence of zinc vacancy-hydrogen complexes in ZnO materials.
Structure and Positron Characteristics of Basic Open Volume Defects in Zirconia
Authors: Melikhova Oksana , Kuriplach Jan , Čížek Jakub , Procházka Ivan , Brauer Gerhard
Published: March 2009

In this contribution we report on the theoretical study of basic vacancy-like defects in cubic zirconia and yttria stabilized zirconia. In particular, we concentrate on oxygen vacancy, zirconium vacancy and oxygen vacancy – yttrium complex. Relaxed atomic configurations of studied defects are obtained by means of an ab initio pseudopotential method within the supercell approach. Positron characteristics, like positron lifetime and binding energy to defects, are calculated using self-consistent electron densities and potentials taken from ab initio calculations.
The Behavior of Oxygen and Defects in Si-Based Semiconductor Studied by Positron Annihilation Techniques
Authors: Deng Wen , Huang Le , Zhu Qi Tao , Wei Ya Qin , Huang Yu Yang
Published: March 2009

Slow positron beam and coincidence Doppler broadening techniques have been used to follow temperature-induced defects and structural changes in Cz-Si with an initial oxygen content of 1.1×1018 cm-3. Oxygen is recognized as a peak at about 11.85×10-3m0c on the ratio curves. For Cz-Si annealed at 480 oC/15h or 600 oC/15h, the ratio curves show the presence of vacancy-like defects, but they are not associated with oxygen. For Cz-Si annealed at 480 oC/15h, then followed by a 600 oC/15h heat treatment, the ratio curves show the signal of O atom. The ratio curves of Cz-Si, thermally treated by a two-step (480oC/15h + 600oC/15h) pre-annealing, followed by a one-step annealing under different hydrostatic argon pressures and annealed temperatures, also show a peak at 11.85×10-3m0c. The height of the peak varies with different samples. Experimental results indicate that the SiO2 film will form on the surface of Cz-Si after the heat treatment.
Defect Study of As-Grown Single Crystal ZnO by Positron
Authors: Ke Jun Yu , Li Hui , Pang Jin Biao , Dai Yi Qun , Wang Zhu , Zhao You Wen
Published: March 2009

ositron lifetime spectroscopy (PAS) and Coincidence Doppler broadening measurements have been performed in as-grown and annealing single crystal ZnO. The temperature dependence observed in annealed ZnO indicates that the defect is removed during annealing. By combining the Doppler broadening measurements, we infer that there isn′t hydrogen filling the zinc vacancy site in the as-grown ZnO due to the same characteristics in CDB for as-grown and annealed ZnO samples
Positron Annihilation on the Surfaces of Single Crystals of Si, SiO2, Graphite and Cu
Authors: Deng Wen , Yue Li , Li Yu Xia , Cheng Xu Xin , Wei Ya Qin , Huang Yu Yang
Published: March 2009

Slow positron beam technique has been applied to measure the Doppler broadening spectra for single crystals of Cu, SiO2, graphite, virgin Si, and Si without oxide film. The results show that the Cu ratio curve shows a high peak due to Cu having 10 electrons in the 3d shells. The ratio curve of SiO2 is higher than that of graphite. For the single crystal of Cu, SiO2, graphite, and Si without oxide film, the S (W) parameters decrease (increase) as positron implantation energy increasing. Defects on the surface lead to higher S (lower W) value. For the virgin Si and the thermally grown SiO2-Si samples, the S (W) parameters increase (decrease) as positron implantation energy increasing. It can be due to Si atom at surface, with two dangling bonds, tend to form silicon oxide with O. The W parameter for the single crystal of Cu is relatively high as compared with that of the single crystals of SiO2 and graphite.
Some Problems of the Free Volume Studies in Porous Polymers Using Positron Annihilation and Auxiliary Techniques
Authors: Shantarovich Victor P. , Gustov V.W. , Yampolskii Y.P. , Belousova E.V. , Polyakova A.V. , Filimonov M.K.
Published: March 2009

Membrane materials and polymer sorbents, polymers with highly developed free volume and specific surface, are of great technical importance. Positron annihilation lifetime (PAL) studies of these materials and some additional experiments give a chance to learn about the character of size distributions of elementary free volumes (EFV) of these materials. Particularly to answer the question whether the distributions of o-Ps lifetimes are of Gaussian type, as it is suggested in a number of publications, or they have some asymmetry or even some multi-component character, also to check some ideas on the ways of o-Ps trapping. In this aspect, large scale of o-Ps lifetimes (pore sizes) in these materials is very important, since enables comparison with the results of auxiliary techniques.