bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and Characterization of Nanostructured Ferrite Materials by a Nitrate-Citrate Self-Combustion Sol–Gel Synthesis
Authors: Trif László , Molnár-Vörös Nikoletta , Tolnai Gyula , Sajó István E. , Mészáros Sándor , Kálmán Erika
Published: March 2009

New chemical synthesis procedure for the preparation of nickel zinc doped W-type
hexagonal barium ferrite and aluminium doped yttrium-iron garnet nanoparticles has been
developed, using the nitrate-citrate sol-gel auto-combustion method (NCSAM). The crystalline
phase attributes, microstructure, morphology, specific surface area, Curie temperature (TC),
permeability, thermal behavior of the as-burnt phase and the heat treated powders were
characterized using XRD, SEM, FT-IR, BET, TG-DTA and AC magnetic permeability with
frequency shift. In the case of the hexaferrite, the pure W-type ferrite phase is formed during 4 hour
annealing at a temperature of 1200 °C, the garnet phase is formed at a lower temperature i.e. 1000
°C. Furthermore it has been confirmed, that the AC magnetic permeabilities of the garnet materials
are strongly depending on the chemical composition.
The Effect of a Rotating Magnetic Field on the Solidification of A356 Alloy Modified by Strontium
Authors: Gergely Gréta , Gácsi Zoltán , Bánhidi Olivér , Kovács Jenő , Rónaföldi Arnold
Published: March 2009

The A356 alloy, which consists of 100-200 ppm modifier, namely strontium was examined.
The samples were solidified unidirectionally, and each sample had a pair which was solidified
in a rotating magnetic field. The microstructure of the samples: morphology and the fraction of
eutectic silicon was studied. The morphology of eutectic Si was very different in the samples - the
samples solidified at different movement velocities – so it was necessary to determine the quantity
of strontium. Magnetic stirring changes both the strontium content and the extent of modification.
This paper describes the investigation methods and the effects of strontium modification.
Hexagonal WO3 Films with Carbon Nanotubes for Sensing Applications
Authors: Balázsi Csaba , Ionescu Radu , Sedlácková Katarína
Published: March 2009

In this work, nanocrystalline hexagonal tungsten oxide was prepared by acidic precipitation from
sodium tungstate solution. TEM studies of nanopowders showed that the average size of the
hexagonal nanoparticles is 30-50 nm. Novel nanocomposites were prepared by embedding a low
amount of gold decorated carbon nanotubes into the hex-WO3 matrix. The addition of MWCNTs
lowered the temperature range of sensitivity of hex-WO3 nanocomposites to NO2 hazardous gas.
The sensitivity of hex - WO3 with Au-decorated MWCNTs to NO2 is at the temperature range
between 25°C and 250°C.
Microstructure and Mechanical Behavior of Ultrafine-Grained Titanium
Authors: Gubicza Jenő , Fogarassy Z. , Krállics György , Lábár János L. , Törköly Tamás
Published: March 2009

Ultrafine-grained titanium was processed by severe plastic deformation (SPD). The SPD
was carried out by equal channel angular pressing (ECAP) at high temperature. The ECAPprocessed
sample was further deformed by conventional techniques such as radial forging and
drawing. The microstructure was characterized quantitatively by X-ray diffraction line profile
analysis and transmission electron microscopy after each step of deformation. The effect of
procesing routes on the mechanical behavior was also studied. It was found that the conventional
deformation processes after ECAP result in further increment in dislocation density and strength at
the expense of ductility.
Impact of Point Defects on the Luminescence Properties of (Al,Ga)N
Authors: Chichibu Shigefusa F. , Uedono Akira , Onuma Takeyoshi , DenBaars Steven P. , Mishra Umesh K. , Speck James S. , Nakamura Shuji
Published: March 2009

Threading dislocations (TDs) in (Al,In,Ga)N semiconductors are known to affect the
luminescence efficiency of near-band-edge (NBE) emissions in bulk films and quantum structures.
However, the principal role of point defects such as vacancies on the luminescent properties has not
been fully understood. In this article, impacts of point defects on the luminescence quantum
efficiency of NBE emissions and on the intensity of deep emission bands will be described, based on
the results of steady-state and time-resolved photoluminescence (TRPL) and positron annihilation
measurements. The room temperature nonradiative lifetime (τNR) of the NBE excitonic
photoluminescence (PL) peak in polar (0001) and (000-1) , nonpolar (11-20) and (10-10), and
zincblende (001) GaN layers prepared by various growth techniques was shown to increase with the
decrease in concentration or size of Ga vacancies (VGa) and with the decrease in gross concentration
of point defects including complexes, leading to an increase in the NBE PL intensity. As the edge TD
density decreased, the concentration or size of VGa tended to decrease and τNR tended to increase.
However, there existed remarkable exceptions. The results indicate that the nonradiative
recombination process is governed not by single point defects, but by certain defects introduced with
the incorporation of VGa, such as VGa-defect complexes. Similar relations were found in AlxGa1-xN
alloy films grown by metalorganic vapor phase epitaxy: i. e. τNR at room temperature increased with
the decrease in the concentration of cation vacancies (VIII) and with the decrease in gross
concentration of point defects. In addition to nonradiative processes, the VIII concentration was found
to correlate with the intensity ratio of characteristic deep emission band to the NBE emission
(Ideep/INBE). For example, Ideep/INBE at low temperature for the deep emission bands at 4.6, 3.8, and 3.1
eV of AlN epilayers grown by NH3-source molecular beam epitaxy had a linear correlation with the
concentration or size of Al vacancies (VAl). Since the relative intensities of 3.1 eV and 3.8 eV bands
increased remarkably with lowering the supply ratio of NH3 to Al (V/III ratio) and growth
temperature (Tg), they were assigned to originate from VAl-O as well as VAl-shallow donor complexes.
The VAl concentration could be decreased by adjusting the V/III ratio and Tg. In the case of AlxGa1-xN
alloys, the concentration or size of VIII and Ideep/INBE at 300 K increased simultaneously with the
increase in x up to approximately 0.7. Similar to the case for GaN and AlN, the deep emission band
was assigned as being due to the emission involving VIII-O complexes.
Effect of the High Energy Milling in the Crystallite Size of WC-Co
Authors: Pinto G.B. , Soares S.R.S. , Gomes Uilame Umbelino , Nascimento Rubens Maribondo , Martinelli Antonio Eduardo , Silva José F.
Published: March 2009

High-energy milling has been used for production of nano-structured WC-Co powders.
During the High-Energy Milling, the powders suffer severe high-energy impacts in the process of
ball-to-ball and ball-to-vial wall collisions of the grinding media. Hard metal produced from nanostructured
powders have better mechanical properties after appropriate sintering process. During the
milling the particles size of WC and Co can be reduced and plastic deformed. In the present work, a
mixture of WC-10%Co was produced by high energy milling. The starting powders of the WC (0.87
μm - Wolfran Bergau) and Co (0.93 μm - H.C.Starck) were used to produce the hard metal. The
influence of the milling time on the particle size distributions and in the lattice strain was
investigated. Milling time of the 2, 10, 20, 50, 70, 100 and 150 hours were used. The powders after
milling were characterized by X-ray diffraction (XRD) and Scanning Electronic Microscopy (SEM).
The results show that 10 h milling were enough to reduce the crystallite size of WC and the increase
of the milling time reduces the crystallite size.
Properties of Porous Ti-35Nb-7Zr-5Ta Processed by the Spacer Method for Use in Biomedical Applications
Authors: Taddei Elisa B. , Henriques V.A.R. , Silva Cosme Roberto Moreira , Cairo Carlos Alberto Alves
Published: March 2009

Ti-35Nb-7Zr-5Ta alloy is a promising new material for a bone graft substitute with good
strength properties and an elastic modulus closer to that of bone than any other metallic material.
TNZT samples until 50 vol % porosity were manufactured using ‘‘space holder’’ technique and
sintering methods. Irregular ammonium carbonate powders were used as a space holder material.
Complete removal carbonate from the green compact was achieved by heating at 200 °C for 5 hours
and subsequent sintering at 1600 °C, with heating rate of 10 °C/min. For the alloy microstructural
characterization, scanning electron microscopy was used. Density was measured by Archimedes
method. The results show that the blended elemental P/M process and the space holder technique
are efficient for the obtainment of highly porous samples. Foams with porosities in the range
between 10% and 50% could be reached.
Effect of High Energy Milling Parameters on Nanostructured Cr3C2-Ni20Cr Powder Characteristics
Authors: Cunha C.A. , Padial A.G.F. , de Lima Nelson Batista , Martinelli J.R. , Correa Olandir Vercino , Ramanathan Lalgudi Venkataraman
Published: March 2009

Cr3C2-NiCr coatings have been used for corrosion and wear resistant applications. In the
last decade, thermal sprayed coatings using nanostructured feed stock of other materials has
exhibited higher hardness, strength and corrosion resistance. Hence, it is anticipated that
nanostructured Cr3C2-NiCr coatings will also exhibit these properties and therefore posses
improved performance characteristics. Preparation of nanostructured feed stock powders is the first
step in the synthesis of nanostructured coatings and mechanical milling is an effective process to
obtain the powders. Preliminary studies in which commercial Cr3C2-NiCr powders were milled in
hexane and gaseous nitrogen revealed that particle and crystallite size were significantly smaller in
powders milled in nitrogen. This paper presents the effect of hexane content and milling parameters
on Cr3C2-Ni20Cr powder characteristics. Use of just sufficient hexane as the milling media reduced
significantly the particle and crystallite sizes.
Effect of the Dispersion of Nanosized Carbides (NbC - TaC) in the Sintered Microstructure of the Stainless Steel 316L
Authors: Gomes Uilame Umbelino , Oliveira L.A. , Soares S.R.S. , Furukava M. , Souza C.P.
Published: March 2009

Sintered stainless steel has a wide range of applications mainly in the automotive
industry. Properties such as wear resistance, density and hardness can be improved by addition of
nanosized particles of refractory carbides. The present study compares the behavior of the sintering
and hardness of stainless steel samples reinforced with NbC or TaC (particles size less than 20 nm)
synthesized at UFRN. The main aim of this work was to identify the effect of the particle size and
dispersion of different refractory carbides in the hardness and sintered microstructure. The samples
were sintered in a vacuum furnace. The heating rate, sintering temperature and times were
20°C/min, 1290°C and 30, 60 min respectively. We have been able to produce compacts with a
relative density among 95.0%. The hardness values obtained were 140 HV for the reinforced
sample and 76 HV for the sample without reinforcement.
Estimative of the Stacking Fault Energy for a FeNi(50/50) Alloy and a 316L Stainless Steel
Authors: de Campos Marcos Flavio , Loureiro S.A. , Rodrigues Daniel , Silva Maria do Carmo , de Lima Nelson Batista
Published: March 2009

The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steel
has been evaluated by means of X-Ray Diffraction (XRD). The average microstrain as function of the
milling time (1/2h, 1h and 8h) was determined from XRD data. The displacement and broadening of the
(XRD) peaks were used for estimate the stacking fault energy (SFE), using the method of Reed and
Schramm. It was estimated SFE=79 mJ/m2 for the FeNi (50/50) alloy and SFE=14 mJ/m2 for the 316L
stainless steel. The better experimental conditions for determining the SFE by XRD are discussed.
Study of Continuos Settling Vessels Operating with Suspensions Previously Floculated
Authors: Nunes J.F. , Lira J.R. , Damasceno João Jorge Ribeiro
Published: March 2009

The settling vessels are equipment destined to solid-liquid separation; usually have
continuous operation, with a circular section, presenting one conic and one cylindrical part. They are
very used in chemical industries: wastewater treatment, minerals industries; to concentrate or to
remove the solids. The solid particle splitting with small granular becomes difficult through the
operation of conventional sedimentation. An expedient very used in the industry is the flocculant
substance addition, whose objective is to promote the precipitation of particles, with decantation
speed is upper than the single one. The present work aim the study of the burst operational
conditions that influence the formation and the stability of these aggregates, the flake, the effect of
pH and the concentration of flocculant using kaolin suspension and genfloc, that contains aluminum
sulfate, as a flocculant; and the capacity of conventional settling vessel, which area of the
transversal remains constant, considering this operational conditions.
Mechanical Properties of Zirconia Toughened Alumina Composites with TZP Partially Nanostructured Sintered by Liquid Fase
Authors: Assis João Marcos K. , Neto Francisco Piorino , de Melo Francisco Cristóvão Lourenço , Nono Maria do Carmo de Andrade
Published: March 2009

A comparative study between alumina added niobia ceramics and two alumina zirconia
composites from nanostructured TZP (7% and 14% weight) was made. On this composites the
zirconia were yttria stabilized and the alumina were submicron structured. As sintering aid a
mixture of magnesia, niobia and talc were used on all samples. The sintering was performed at
1450 oC during 60 minutes. The characteristic grain size and shape of an alumina and zirconia
powders, aggregates and agglomerates were characterized. The sintering ceramics were evaluated
through hardness, fracture toughness and 4 point bending test. Weibull statistic was applied on the
flexural results. Although the fracture toughness result from ZTA were lower, and seems to be
affected by the liquid fase, the hardness and Weibull modulus were higher than alumina niobia. The
grains size and the homogeneity of its distributions on the microstructure of this ceramics was
correlated to these higher values. The results from these alumina zirconia composites showed a
potential to apply as a ballistic armor material.
Sintering of Y2O3-Stabilized ZrO2 Powders Obtained by Different Chemical Methods
Authors: Salem R.E.P. , Chinelatto Adilson Luiz , Chinelatto Adriana Scoton Antonio
Published: March 2009

The chemical methods allow obtaining powders with high reactivity and chemical
homogeneity. This work studied the sintering of Y2O3-stabilized ZrO2 powders produced by
polymerization routes. In the three methods used were obtained powders via formation of gels,
which were characterized by spectroscopy in the infrared. After the gel calcinations, the powders
obtained were characterized by X-ray diffraction and scanning electronic microscopy (SEM).
Among the different chemical methods, there were differences in the coordination of the metallic
ions, which caused differences in the thermal behavior, reactivity, size and form of the particles of
the powders. The powders were pressed and sintered at 1400 and 1600°C for 2 hours. The bodies
sintered were characterized by SEM, apparent density and dilatometry. The average size of the
particles varied with the method, and the smallest particles were obtained by Pechini method. PCS
method showed a strong reactivity of the powder and it was already partially sintered even in the
step of elimination of organic substances. Similarly, the sintered compacts presented different
properties with each other, and the compacts obtained by PEG/FA method had the best
microstructure.
SiC Infiltred Diamond Composites
Authors: Bobrovinitchii Guerold Sergueevitch , Skury Ana Lúcia Diegues , Osipov Alexsander , Tardim Rômulo Crespo
Published: March 2009

Polycrystalline SiC-diamond composites have been fabricated by high pressure and high
temperature, HPHT, sintering using a Si infiltration method. However, infiltration of liquid silicon
around the diamond particles results not only in SiC but also in free silicon, which causes
deterioration of the composite properties. In this work, a novel sintering procedure was developed
to avoid the formation of free silicon in the composite structure. A disc composed of a mixture of
graphite and silicon was first press-molded at room temperature. The disc was then placed above
the diamond powder inside a high pressure chamber used for the HPHT sintering process. This
arrangement permitted to preferentially form liquid Si in a C solution, which infiltrates in between
the diamond particles. Using this procedure, free silicon formation is inhibited and the SiC-diamond
composite forms a rigid structure with improved properties.
Effect of Different Tempering Stages and Temperatures on Microstructure, Tenacity and Hardness of Vacuum Sintered HSS AISI T15
Authors: Lima E.P.R. , das Neves Maurício D. M. , Nogueira Rejane A. , de Oliveira L.G.C. , Ambrozio Filho Francisco
Published: March 2009

The purpose of this study is to evaluate the effect of the stages and tempering
temperatures in the microstructure, tenacity and hardness of the vacuum sintered high speed steel
AISI T15. The material was uniaxial pressing at 700 MPa and sintered in a vacuum furnace at
1275°C. After that, different samples of the materials were submitted to the annealing treatment at
870°C, quenching at 1235°C and tempering (single, double and triple) at 540, 550 and 560°C.
Concluded the treatments, Rockwell C measurements of hardness were accomplished and, to
evaluate the toughness of the material, TRS (Transverse Rupture Strength) tests were done. Later
on, the materials were submitted to the metallographic preparation for microstructure analysis in
optical microscopy, SEM, EDX and X-ray diffraction. Finally, each property analyzed was
evaluated and correlated with the different tempering stages and temperatures accomplished.
Microstructural and Mechanical Characterization of Sintered Hydroxyapatite Samples
Authors: de Oliveira Marize Varella , Schaerer Magna Monteiro , Santos Silvia R. A. , Caminha Ieda Maria V. , Rossi Antonella M.
Published: March 2009

Despite of the wide use of hydroxyapatite (HA) for bone repair and regeneration, its
brittleness has limited clinical application to less stressed body parts. Thus, evaluation of HA
mechanical properties has been an important research matter. The aim of this study is to assess the
compressive strength of a stoichiometric HA with 1.66 Ca/P molar ratio, synthesized by
hydrothermal method. Cylindrical samples were processed by uniaxial compacting, followed by
sintering. Compressive strength of cylindrical samples with 2.0 medium diameter/height ratio was
measured according to ASTM C 1424. Load to failure divided by the cross-sectional area of the
samples were reported and microstructural characterization was made by MEV-EDS. The
compression strength results were compared to values reported in the literature.
Catalytic Evaluation of Al2O3-ZrO2 Supports Used in the Reduction of NO with CH4
Authors: de Melo Costa Ana Cristina Figueiredo , de Souto Viana Kaline Melo , Porto M.G.C. , Souza E. , Andrade Heloysa Martins Carvalho , Gama Lucianna , Lira Hélio Lucena , de Oliveira J.B.L.
Published: March 2009

The aim of this work is to prepare and characterize Al2O3-ZrO2 powders by Pechine
method and to evaluate them as supports for palladium catalysts in the selective reduction of NO
with CH4. The effect of aluminum ion on the final characteristics of the zirconia powder is also
investigated. The catalytic supports were characterized by X-ray diffraction (XDR), scanning
electron microscopy (SEM) and catalytic activity. The XRD data showed the formation of tetragonal
zirconia phase, with crystallite size of 6.3 and 6.1 nm for the supports prepared with 0.1 and 0.5
moles of Al3+, respectively. Both supports showed porous and homogeneous agglomerates.
Pd/Al2O3-ZrO2 catalysts were active NO reduction by CH4.
Use of Kaolin Processing Waste for the Production of Mullite Bodies
Authors: Brasileiro Maria Isabel , Menezes Romualdo Rodrigues , Farias M.O. , Lira Hélio Lucena , Neves Gelmires Araújo , de Lima Santana Lisiane Navarro
Published: March 2009

Mullite is a versatile material used in traditional and advanced ceramic, due to low
thermal expansion, high thermal shock and creep resistance. The production of waste from ore
industry is a problem that is increasing nowadays. The kaolin processing industry produces residue
rich in Al2O3 and SiO2. These oxides are good precursors to produce mullite. The aim of this work
is to use the residue from kaolin industry to produce mullite ceramic bodies. It was studied alumina,
clay and residue from kaolin processing as raw materials. The material was dried and pressing in
uniaxial press (30MPa). The samples were sintered at temperatures of 1450oC, 1500oC, 1550oC and
1600oC. The ceramic bodies were characterized by X-ray diffraction. The density was measured by
Archimedes method and the flexural strength by the three point bending technique. The results
showed that is possible to produce mullite with high amount of waste from kaolin processing.
Simulating Sintering Process in SmCo5 Magnets
Authors: de Castro José Adilson , de Campos Marcos Flavio
Published: March 2009

SmCo5 sintered magnets are produced according the following main processing: milling
until single crystal particle size, compaction and sintering. It is necessary high density to maximize
remanence, but small grain size to maximize coercivity. A sintering model able to incorporate both,
the densification rate and the grain growth rate, is described. This makes easier to find the better
sintering conditions for optimization of the magnetic properties (coercivity and remanence). The
presented model represents a refinement of previous sintering models, because it takes into account
the coupled effects of grain size evolution and shrinkage.
Processing of the Fe3Si Alloy from Prealloyed Powder Fe45Si by Metal Injection Molding
Authors: da Silva Doublas José , Silva Aline , Machado Ricardo , Wendhausen Paulo A.P.
Published: March 2009

The known process as Metal Injection Molding is derived from the conventional powder
metallurgy (M/P) being an alternative for production of parts with complex geometry, great
dimensional precision and freedom of chemical composition. The present work has the objective to
evaluate the processing of the Fe3Si alloy sintering in the vacuum furnace using as raw materials
iron powder carbonyl and prealloyed powder Fe45Si with D90<10-m. Properties of microhardness,
density, coercivity, magnetic permeability, and chemical composition was evaluated. The obtained
results were compared with what is presented in the literature for parts processed by conventional
ways and with parts processed by M/P. A density of 7,620 kg/m3, a coercive field (Hc) of 101.14
A/m, a relative maximum permeability of 5,484 and a residual induction of 1.1 T was achieved by
MIM. Comparing with conventional processes (where 100% of densification is reached), the MIM
process results were worse, however they were better than P/M.
Study of the Aerosol Concentration Inside the Duct of a Plate-Wire Electrostatic Precipitator
Authors: Valdés E.E. , Coury José Renato
Published: March 2009

The electrostatic precipitator (ESP) is usually employed by industries for the removal of
aerosol particles from gaseous streams. The behavior of the particles inside the collection duct is of
great interest as a tool for optimizing precipitator design and performance. In this work, a
laboratory scale ESP (0.6m long, 0.3m high and 0.2m wide) was tested with electric fields of 250,
350 and 450 kV/m at a gas velocity of 1.0 m/s. The discharge electrode was located at 0.30 m from
the beginning of the collector plate. The test aerosol was constituted of a phosphatic concentrate
dispersed in air. Particles were sampled isokinetically in situ in the duct, at five different
longitudinal positions. The experimental results for the aerosol studied show that concentration
profile of particles are affected by the electrical field at considerable upstream distances from the
charging electrode. The particle collection starts well before the charging electrode, characterizing a
strong entrance effect, often disregarded in the existing correlations for predicting ESP
performance.
Study of Soft Magnetic Nickel-Iron Based Alloys Processed by Powder Injection Molding
Authors: Lopes Leonardo Ulian , Shoda Juliana A. , Silva Aline , Machado Ricardo , Rodrigues Daniel , Wendhausen Paulo A.P.
Published: March 2009

Ni-Fe based soft-magnetic alloys, processed via Metal Injection Molding (MIM), were
investigated regarding the influence of processing route on final magnetic properties and compared
to fully dense cast materials. The process variations included high and low temperature debinding,
different sintering routes and the application of hot isostatic pressing (HIP). The different densities
resulting from the process variations were related to maximum magnetic permeability. Results have
shown that density, in the range between 7,5g/cm³ and 8,0g/cm³, does not have significant influence
on the maximum permeability, allowing cost-effective process routes. It was also verified that fullydense
cast alloys still exhibits superior properties, with lower coercive fields and higher
permeability, but results achieved after HIP process overcame even the values of these commercial
grade alloys.
An Optimization Approach to the Displacement Volumes for External Spur Gear Pumps
Authors: Huang Kuo Jao , Chang Wen Ruey , Lian Wun Chuan
Published: March 2009

To increase volume displacement is always concerning in designing external gear pumps
(EGPs). Therefore, an approach of optimization analysis intending to enhance their displacement
capability is proposed in this study. Through that, design parameters of the spur gears in the pumps are
systematically resulted to achieve their optimal volume displacements. Parametrically, a CAD model
to visualize the designed gear of the optimal design is also created. Firstly, the study derives tooth
profile equations by using the coordinate transformation and equation of meshing for gears on a rack
cutter profile. Then, an analytic formula represented the enveloping area by an involute curve is
derived. Next, volumes of output and trapped backflow of the EGP are achieved. Therefore the net
output volume can be calculated accurately and efficiently. After that, the optimization analysis to
maximize the volume displacement is performed. Through that, optimal design parameters for the
pumps are achieved under assigned constraints for considerations of design and manufacturing.
Additionally, influences of module, pressure angle, and addendum correction factor for the gears in
the pumps on their displacement capability are also investigated. Additionally, flowrate fluctuation
characteristics under different pressure angles of gears are finally discussed.
Creep Deformation / Oxidation Behavior of Re-Cr-Ni Diffusion Barrier Coated Hastelloy-X at 970°C in Air
Authors: Hayashi Shigenari , Sakata Mikihiro , Ukai Shigeharu , Narita Toshio
Published: March 2009

High temperature oxidation / creep deformation behavior of a diffusion barrier coated
Hastelloy-X alloy, with large grain size ~500μm, was investigated at 970°C in air with external
tensile stress of 22.5, 27.5, 32, and 40MPa. The diffusion barrier coating formed on Hastelloy-X
consisted of a duplex structure with an inner diffusion barrier layer of Re-Cr-Ni alloy, and an outer
oxidation resistant layer of β-NiAl. Un coated bare Hastelloy-X alloy with same grain size was also
examined under the same conditions for comparison. The composition of the as-coated diffusion
barrier coating was (15~21)Ni, (33~37)Cr, (30~33)Re, (11~15)Mo, and (9~14)Fe. This composition
corresponds to σ-phase in the Ni-Cr-Re ternary system, which is known as a topologically close
packed, TCP phase. The composition of this diffusion barrier layer did not change during the
experiment. The oxide scales formed after creep testing on the coated and un-coated alloy surfaces
were needle-like θ-Al2O3, and Cr2O3 with small amount of FeCr2O4, respectively. Grain boundary
oxidation was also found in the subsurface region of the un-coated alloy. The Al2O3 scale exhibited
severe spallation, and many cracks were formed perpendicular to the stress direction. However, no
spallation or cracks were observed in the Cr2O3. The creep rupture times for the diffusion barrier
coated alloy were about 1.5 times longer than those for bare alloy at all creep stress conditions. The
fracture surface after rupture indicates that fracture occurred along alloy grain boundaries in both the
coated and un-coated alloy substrate. Many cavities and cracks were observed within the diffusion
barrier coated alloy substrate. These cavities and cracks tended to propagate from the substrate
toward the diffusion barrier layer, and then stopped at the Re-Cr-Ni / β-NiAl interface. Cracks formed
in the un-coated alloy initiated at the tip of grain boundary oxides, and propagated into alloy
substrate. However no major cavities were observed inside the alloy substrate. The stress index, n, for
both specimens was about 6, and this indicates that the deformation mechanism of both samples was
dislocation creep. These results suggest that the Re-Cr-Ni diffusion barrier layer acts as a barrier
against the movement of dislocations at the interface with the alloy surface.
Enigmatic Moisture Effects on Al2O3 Scale and TBC Adhesion
Authors: Smialek James L.
Published: March 2009

Alumina scale adhesion on high temperature alloys is known to be affected primarily by
sulfur segregation and reactive element additions. However adherent scales can become partially
compromised by excessive strain energy and cyclic cracking. With time, exposure of such scales to
moisture can lead to spontaneous interfacial decohesion, occurring while the samples are
maintained at ambient conditions. Examples of this Moisture-Induced Delayed Spallation (MIDS)
are presented for NiCrAl and single crystal superalloys, becoming more severe with sulfur level and
cyclic exposure conditions. Similarly, delayed failure or Desk Top Spallation (DTS) results are
reviewed for TBC’s, culminating in the water drop failure test. Both phenomena are discussed in
terms of moisture effects on bulk alumina and bulk aluminides. A mechanism is proposed based on
hydrogen embrittlement and is supported by a cathodic hydrogen charging experiment.
Hydroxylization of aluminum from the alloy interface appears to be the relevant basic reaction.
Characterization of TBC Systems with NiPtAl or NiCoCrAlYTa Bond Coatings after Thermal Cycling at 1100°C: A Comparative Study of Failure Mechanisms
Authors: Vande Put Aurélie , Oquab Djar , Monceau Daniel
Published: March 2009

During service, TBC can suffer degradation by CMAS, FOD, erosion or spallation.
Whereas the first three are due to foreign particles, the last one is related to thermal cycling. When
subjected to high temperature exposures followed by rapid coolings under oxidizing conditions, a
TBC system undergoes morphological changes and stress development. This will initiate cracks
which propagate and finally lead to failure by spallation. Consequently, the aim of the present study
is to understand better the mechanisms responsible for such spallation events. Two kinds of TBC
systems with different bond coatings (NiCoCrAlYTa or Pt-modified nickel aluminide bond
coatings) are thermally cycled. Subsequently, SEM investigations on TBC systems after spallation
concentrate on failure path, defect, morphological and microstructural changes to propose way for
improving TBC system lifetime.
Compositional Factors Affecting the Oxidation Behavior of Pt-Modified γ-Ni+γ’-Ni3Al-Based Alloys and Coatings
Authors: Mu N. , Izumi Takeshi , Zhang L. , Gleeson Brian
Published: March 2009

Many high-temperature coatings rely on the formation of a continuous and adherent
thermally grown oxide (TGO) scale of α-Al2O3 for extended resistance to degradation. For instance,
the durability and reliability of thermal barrier coating (TBC) systems in gas turbines are critically
linked to the oxidation behavior and stability of an alumina-forming β-NiAl-based bond coat. This
study focuses primarily on the development of unique Pt+Hf-modified γ′-Ni3Al+γ-Ni coating
compositions that form highly adherent, slow-growing TGO scales during both isothermal and
cyclic oxidation at high temperature. Recent findings on the isothermal and cyclic oxidation
behavior of γ′+γ alloys and coatings will be discussed, with particular emphasis on the effects of Pt,
Al and Hf contents and distributions. Inferred reasons for the observed “Pt effect” will also be
presented.
Corrosion Mechanisms of Ni-Base Alloys in Pressurized Water Reactor Primary Conditions
Authors: Marchetti Loïc , Perrin Stéphane , Raquet Olivier , Pijolat Michèle
Published: March 2009

Oxidation mechanism of Alloy 690 has been investigated in Pressurised Water Reactor
(PWR) primary coolant conditions (325°C, aqueous hydrogenated media). Experiments performed
with gold marker and RBS technique reveal that the passive film formation is the consequence of an
anionic mechanism. This result is confirmed by experiments achieved with two sequences of
corrosion in a H2
16O media and in a mixed H2
16O/ H2
18O media. The localisation of 18O by SIMS
analysis in the thin passive layer underlines an oxidation mechanism due to oxygen diffusion by
short circuits (like grain boundaries) in the oxide scale. Moreover grain boundary diffusion
coefficient in chromite like oxide was estimated to be in the range 2 10-18 – 1 10-17 cm2.s-1 and
compared to values extrapolated from higher temperature.
The Effect of Ca-Rich Deposits on the High Temperature Degradation of Coated and Uncoated Superalloys
Authors: Jung Kee Young , Pettit Frederick S. , Meier Gerald H.
Published: March 2009

When gas turbines use alternate fuels, such as syngas derived from coal, ash from the
fuels can deposit on turbine hardware. These deposits can cause substantial corrosion of the
hardware which may have significantly different characteristics than Type I and Type II hot
corrosion. The composition of the ash is determined by the mineral matter in coals, which often
have kaolinite (Al2O3·2SiO2·2H2O), pyrites (FeS2), and calcites (CaCO3) as major components.
This study was directed at degradation produced by CaO and CaSO4 and comparing it with the
attack induced by Na2SO4 deposits.
The alloys GTD 111, IN 738, and René N5, as well as these alloys coated with CoNiCrAlY and
platinum aluminide, were exposed to conditions relevant to corrosion induced using alternative
fuels. The initial test conditions involved a number of deposits including Na2SO4, CaO, and CaSO4
in dry and wet (pH2O = 10.1 kPa, 0.1 atm) air at 950oC. The most severe degradation occurred with
CaO deposits.
Specimens of the three alloys were subsequently exposed to cyclic oxidation conditions at 950oC
with deposits of CaO in dry and wet air. All three alloys were attacked more severely when CaO
deposits were present and this attack became even more severe in wet compared to dry air.
However, the increase in attack caused by the presence of water vapor was small compared to the
attack caused by the CaO deposits. The degradation induced via CaO deposits caused more severe
degradation of René N5 compared to GTD 111 and IN 738.
Tests using CaO deposits and cyclic oxidation conditions at 950oC in dry and wet air were also
performed for the two coatings on the three alloy substrates. Both coatings were significantly
degraded by attack induced by the CaO deposits. No effect of the alloy substrates on coating
performance was apparent. Mechanisms for the effects of Ca-rich deposits on superalloy and
coating degradation are discussed.
Synchrotron Radiation X-Ray Scattering Techniques for Studying the Micro- and Nanostructure of Wood and their Relation to the Mechanical Properties
Authors: Müller Martin
Published: March 2009

X-ray scattering techniques have been a very useful tool for the non-destructive analysis of the wood structure. X-rays are sensitive to structural parameters such as the composite structure of wood cell walls, the crystal structure of cellulose microfibrils and their helical arrangement in the cell wall, which is usually described by the microfibril angle (MFA). With the availability of synchrotron radiation sources novel experiments on wood have become possible. The increased flux of X-rays makes the in situ and time-resolved investigation of structural changes upon mechanical stress possible. The low-divergence synchrotron radiation X-rays can be focused down to sub-micrometer size, enabling scanning studies of the wood nanostructure with (sub-)microscopic position resolution. This chapter highlights very recent advances in the understanding of wood micro- and nanostructure, which were only possible using synchrotron radiation. Examples include the MFA determination in the individual layers of the secondary cell wall, the imaging of the helical structure of the cellulose microfibrils in the cell wall, lattice strain as induced by applied mechanical stress and the structural changes of different wood types under external tensile stress.
3C-SiC Heteroepitaxy on (100), (111) and (110) Si Using Trichlorosilane (TCS) as the Silicon Precursor.
Authors: Anzalone Ruggero , Severino Andrea , D'Arrigo Giuseppe , Bongiorno Corrado , Fiorenza Patrick , Foti Gaetano , Condorelli Giuseppe , Mauceri Marco , Abbondanza Giuseppe , La Via Francesco
Published: March 2009

The aim of this work is to improve the heteroepitaxial growth process of 3C-SiC on Si substrates using Trichlorosilane (SiHCl3) as the silicon growth precursor. With this precursor it has been shown that it is possible to simultaneously increase the growth rate of the process and avoid the nucleation of silicon droplets in the gas phase. Growth experiments were conducted on three (3) Si substrate orientations in order to assess the impact of the Si substrate on the resulting 3C-SiC film. X-ray Diffraction (XRD), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) analysis show the important role of the substrate orientation for the growth process. The different orientation of the substrate modifies the morphology of the 3C-SiC crystalline structure, mostly by changing the density of micro-twins and stacking faults inside the film.
Effect of Process Parameters on Material Removal Rate in Chemical Mechanical Polishing of 6H-SiC(0001)
Authors: An Joon Ho , Lee Gi Sub , Lee Won Jae , Shin Byoung Chul , Seo Jung Doo , Ku Kap Ryeol , Seo Heon Decok , Jeong Hae Do
Published: March 2009

2inch 6H-SiC (0001) wafers were sliced from the ingot grown by a conventional physical
vapor transport (PVT) method using an abrasive multi-wire saw. While sliced SiC wafers lapped by a
slurry with 1~9㎛ diamond particles had a mean height (Ra) value of 40nm, wafers after the final
mechanical polishing using the slurry of 0.1㎛ diamond particles exhibited Ra of 4Å. In this study,
we focused on investigation into the effect of the slurry type of chemical mechanical polishing (CMP)
on the material removal rate of SiC materials and the change in surface roughness by adding abrasives
and oxidizer to conventional KOH-based colloidal silica slurry. The nano-sized diamond slurry
(average grain size of 25nm) added in KOH-based colloidal silica slurry resulted in a material
removal rate (MRR) of 0.07mg/hr and the Ra of 1.811Å. The addition of oxidizer (NaOCl) in the
nano-size diamond and KOH based colloidal silica slurry was proven to improve the CMP
characteristics for SiC wafer, having a MRR of 0.3mg/hr and Ra of 1.087Å.
Effect of Al3(Sc,Zr) Particles on Tensile Properties of an Al-Zn-Mg-Cu-Sc-Zr Alloy
Authors: Senkov O.N. , Shagiev M.R. , Miracle D.B.
Published: March 2009

Small additions of Sc and Zr may considerably improve both strength and ductility of 7000 series aluminum alloys, which is associated with precipitation of fine coherent Al3(Sc,Zr) particles. These particles also increase resistance to recrystallization and promote formation of a stable refined microstructure. Because of very low equilibrium solubility of Sc and Zr in Al alloys, a supersaturated solid solution of these elements in the Al matrix presented after casting is responsible for precipitation of the Al3(Sc,Zr) particles during subsequent heat treatment, while the strengthening effect depends on the particle size and number density. Therefore, it is necessary to optimize precipitation of the Al3(Sc,Zr) particles, in order to achieve superior balance of mechanical properties. In the present work, the effect of heat treatment conditions on microstructure and tensile properties of a developmental 7000 series Al alloy SSA018 modified with Sc and Zr was studied, with special emphasis on the analysis of size and number density of the Al3(Sc,Zr) particles, and their effect on the strength increase.
Plastic Flow and Grain Refinement under Simple Shear-Based Severe Plastic Deformation Processing
Authors: Orlov Dmitry , Todaka Yoshikazu , Umemoto Minoru , Beygelzimer Yan , Horita Z. , Tsuji Nobuhiro
Published: March 2009

In the present work, effects of loading scheme and strain reversal on structure evolution are studied by using high pressure torsion (HPT) and twist extrusion (TE) techniques. High purity aluminum (99.99%) was processed at room temperature up to a total average equivalent strain of ~4.8 by TE and HPT with two deformation modes: monotonic and reversal deformation with a step of 12˚ rotation. It was revealed that microstructural change with straining observed in pure Al was a common consequence of the SPD processing and was not affected significantly by the loading scheme. At the same time, it was found that strain reversal retarded grain refinement in comparison with monotonic deformation.
Hot Formability and Texture Formation in Al Alloys
Authors: Hirsch Jürgen
Published: March 2009

The effect of plastic deformation of Aluminium alloys at elevated temperatures is described and its effects on texture evolution in Aluminium and its alloys. The softening mechanisms involved are recovery, recrystallization and grain boundary sliding which reduce strain hardening and affect plastic deformation also in industrial fabrication and forming processes of Aluminium alloys, like (hot) forming, rolling, extrusion and superplastic forming. These effects that control high temperature formability and the resulting textures and final properties are described.
Nanoindentation of Silicon
Authors: Nagy Péter M. , Horváth P. , Pető Gábor , Kálmán Erika
Published: March 2009

The nanoindentation behaviours of single crystalline silicon samples has gained wide attention in recent years, because of the anomaly effects in the loading curve, caused by the pressure induced phase transformation of silicon. To further enlighten the phenomenon bulk, ion-implanted, single crystalline Si samples have been studied by nanoindentation and by atomic force microscopy. The implantation of Si wafers was carried out by P+ ions at 40 KeV accelerating voltage and 80 ions/cm2 dose, influencing the defect density and structure of the Si material in shallow depth at the surface. Our experiments provide Young’s modulus and hardness data measured with Berkovich-, spherical- and cube corner indenters, statistics of the pop-in and pop-out effects in the loading- and unloading process, and interesting results about the piling-up behaviour of the Si material.
Long-Term Heat Treatments on Ti6Al4V-SiCf Composite. Part II - Mechanical Characterization
Authors: Deodati Paolo , Donnini Riccardo , Montanari Roberto , Testani Claudio , Valente T.
Published: March 2009

Ti6Al4V-SiCf composite, manufactured by Hot Isostatic Pressing (HIP) at Centro Sviluppo Materiali, has been submitted to long-term heat treatments (up to 1000 hours) at 400 and 600°C. The mechanical properties of the material, in as-fabricated condition and after heat treatments, have been investigated by instrumented indentation (FIMEC), dynamic modulus, tensile and fatigue tests. For comparison some experiments have been carried out also on the monolithic Ti6Al4V alloy. Results show that heat treatments, also the most severe examined here, do not produce remarkable variations of mechanical characteristics. In agreement with the microstructure examinations presented in part I, this behaviour, quite promising for future aeronautical applications, can be primarily ascribed to the stability of fibre-matrix interface.
Constitutive Equations in Creep of the AE44 Magnesium Alloy
Authors: Spigarelli Stefano
Published: March 2009

The creep behaviour of the AE44 magnesium alloy was described by means of a variation of the composite model, already successfully used to analyse the behaviour of die-cast Mg-Al alloys. Since the microstructure of these alloys is constituted by primary Mg globules surrounded by a divorced eutectic formed by supersaturated a-Mg and precipitates, these materials were compared to a composite with soft (globules) and hard (divorced eutectic) regions, both deforming with a similar strain rate during creep. The strengthening role of the precipitates formed in the hard region during cooling from injection temperature and during creep was expressed by introducing a threshold stress. The agreement between experimental data and model was very good.
New Lean Duplex Stainless Steels for Structural Applications
Authors: Calliari Irene , Dabalà Manuele , Ramous Emilio , Straffelini Giovanni
Published: March 2009

The continuous improvement of the applications of duplex stainless steels (DSS) is justified mainly by their excellent corrosion resistance in very aggressive environments and by their mechanical strength, often twice than that of conventional austenitic grades. Therefore more extensive applications have been suggested, like constructions, structural components, automotive applications, etc. However for such not advanced but quantitatively important applications the base cost of the alloy is one of the more constraining features. A way to obtain leaner alloys is to reduce the Ni content and to compensate with manganese and nitrogen additions. In the present paper the structural and mechanical properties of two low Ni duplex grades are analyzed in order to investigate the structural stability of the austenite against its possible transformation to martensite and the secondary phase’s precipitation. The detailed characterization has been performed with SEM-EDS on as received and heat treated (600-850 °C) alloys. A limited precipitation of chromium carbides and nitrides at the grain boundaries has been detected in both grades. The martensite formation has been revealed only in the 2101 grade. With regard to the impact toughness the behaviour of 2101 grade is quite similar to that of the common DSS, while in the 2304 the drastic drop of toughness is avoided. The corrosion behaviour of both grades in aggressive chloride environments is quite similar to that of austenitic AISI 304 grade.
New Model for Characterization of Dynamic Recrystallization and Prediction of Grain Size Applied to Two Wrought Magnesium Alloys
Authors: Rieiro Ignacio , Castellanos Jesus , Carsí Manuel , Muñoz Julio , Ruano Oscar
Published: March 2009

A model for describing the plastic flow has been developed. The model is based on a strain dependent Garofalo equation and predicts the variation with strain of grain size refinement by dynamic recrystallization using non-linear optimization methods. The predictions have been applied to two wrought magnesium alloys, AZ31 and AZ61 and are in good agreement with experimental data.