bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Tool Geometry in the Friction Stir Welding of AA6082-T651
Authors: Louro Rui , Gouveia Helena , Brioso Paulo
Published: March 2009

The Friction Stir Welding (FSW) process has a large industrial potential in the field of
joining lightweight alloys. Due to the increasing industrial use of aluminium alloys the benefits
provided by this technology are very appealing. However, this potential has not, until this time,
become a reality due to the lack of relevant available information concerning the process. The lack
of information is especially serious in regards to the welding tools. This component, whose
importance in the FSW process cannot be overstated, has not been the subject of extensive
published research due mainly to the difficulties related to the modelling of the FSW process, which
means that all of the development in this field has to be conducted through a trial and error
approach. This approach entails significant costs and success risks, thus reducing the capability of
R&D institutions to carry out extensive research. The objective behind the work detailed in this
paper is the assessment of the effects of the welding tool geometry and features in the weld quality
and process productivity. The work was carried out via an experimental procedure, which consisted
of carrying out several welds using different pin lengths, pin diameter, pin geometry and shoulder
diameter. The geometries that were used are based on known geometries from literature and new
concepts. Due to practical limitations the study was conducted using a 3mm thick AA 6082-T6 butt
joint configuration. The quality of the welds was assessed through destructive and non destructive
testing, namely a visual inspection, an x-ray and a macrographic examination. These results can
then be used to correlate the effects of the different tool geometries with the weld quality and
productivity. The process productivity can be, according to [1], directly related to the welding
speed, this is due to the near absence of welding consumables in the FSW process, leading to the
predominance of fixed costs. The results pertaining to this work enable a better comprehension of
the manner by which the tool geometry influences the weld quality and the process productivity,
thus providing a stepping stone in the ongoing task of optimizing and modelling of the FSW
process. The results presented in this paper may also be useful when extrapolated to other materials
and thicknesses.
Damage Assessment of Mullite Ceramic Foams in Radiant Gas Burners
Authors: Oliveira Fernando A. Costa
Published: March 2009

The damage imposed on open-cell mullite ceramic foams was evaluated in pre-mixed
radiant gas burners. After exposure to the prevailing combustion environment, foams suffered
moderate strength degradation as a result of thermal stresses being imposed on the material during
service. There was evidence of chemical attack during combustion although thermal shock
measurements suggest that damage sustained by the foams results mainly from thermal shock rather
than chemical degradation. Indeed, samples from burners subjected to ageing tests did not show
additional damage compared to those subjected to short ageing tests indicating that most of damage
occurred during start-up. For comparison purposes, a set of ceramic foam samples were subjected to
a water quench test so that the extent to which the foams were damage by exposure to the
combustion environment, under well controlled conditions, could be established. The strength
retained after thermal shock by open-cell mullite foams decreased gradually with increasing quench
temperatures. This suggests a cumulative damage mechanism reflecting an increase in damage
throughout the material rather than sudden failure owing to propagation of pre-existing cracks along
a plane. Damage in mullite foams was mainly localised at the top layer of the burners where higher
temperatures and steeper thermal gradients were imposed on the material. Surprisingly, needle-like
mullite crystals with a large aspect ratio were also found to have grown at the surface of the burners
via a vapour feed gas-liquid catalyst-solid needle-like growth (VLS) mechanism.
Dynamic Phenomena during Sessile Drop Measurements due to Oxide Layer Disruption
Authors: Udvardy Oliver , Lovas Antal
Published: March 2009

The wetting phenomenon between solids and liquids has an outstanding role in several
technological processes [1, 2]. The knowledge of physical and chemical factors acting on the
surface tension is needed to ensure the successful processing in casting, brazing and sintering. The
surface oxide layer influences the wetting conditions and makes difficult the exact measurement of
contact angle [3]. In this paper the effect of oxide layer disruption and recovery was observed using
a high speed camera.
Assessment of Laser-Cut Quality on the Basis of Acoustic Emission Signals Captured with a PZT Sensor
Authors: Grum Janez , Kek Tomaž
Published: March 2009

The paper describes an analysis of the AE signals captured with PZT sensor during and
after laser cutting. In the course of cutting the continuous AE signals are treated in a defined time
interval. After cutting, bursts of acoustic emission will occur. They are due to solidification of the
molten material and cooling of the laser-cut surface. The results shown refer to cutting of steel plate
DC04 and of austenitic stainless steel plate X5CrNi18-10. Both plate types are frequently used in
automobile industry, where, because of mass production, optimisation of the cutting process is
desired. Numerous laser-cutting conditions assuring different quality levels of the cut made were
chosen. It was proved that the laser cutting conditions had a significant influence on the amplitude
value and intensity of the continuous signal and AE activity after the termination of laser cutting.
Separately it was also confirmed that there was a relation between the measured signal and laser-cut
quality, which is shown, to a large extent, by the presence of dross at the lower edge of the cut.
Electrospinning of PVA/Carbon Nanotube Composite Nanofibers: The Effect of Processing Parameters
Authors: Molnár Kolos , Košt’áková Eva , Mészáros László
Published: March 2009

Poly(vinyl alcohol)/carbon nanotube (CNT) composite nanofibers were processed by
both conventional and needleless electrospinning method. The effect of the processing parameters
on the possibility of manufacturing was investigated. The results were evaluated by surface tension
and conductivity measurements. For the investigation of surface morphology scanning electron
microscopy (SEM) was used. It was concluded that surface treatment of carbon nanotubes was
necessary for needleless electrospinning. Lower surface tensions were better for this process but the
effect of conductivity was not so significant.
A Complex Measuring and Evaluation System for Determination of Forming Limit Diagrams
Authors: Kovács Péter , Tisza Miklós
Published: March 2009

Forming limit curves are very important for the prediction of failure during sheet metal
forming both in practical forming operations and particularly in numerical simulations. The
reliability of numerical simulations in sheet metal forming processes is strongly influenced by the
reliability of forming limit curves. Therefore, both the theoretical aspects and the experimental
determination of the forming limit curves are challenging problems for scientific researchers and
industrial practitioners as well. There are various experimental techniques and mathematical models
used to determine the forming limit curves. In spite of the standardization efforts made recently by
several institutions world wide, there are still significant differences in determining the forming
limit curves. Recently, a new, complex measuring system capable for the automatic determination
of FLCs was installed at the Department of Manufacturing Engineering. In this paper, first a short
overview will be given on the theoretical background of FLCs, then the application of the complex
measuring system will be shown.
Investigation of the Microstructure and Hardness of SiCP Reinforced Aluminum Matrix Composites
Authors: Makszimus Andrea , Gácsi Zoltán , Gür C. Hakan
Published: March 2009

The purpose of this study is to find a relationship between the parameters describing the
microstructural homogeneity of SiC particle reinforced Al metal matrix composites. The Al-SiC
powder mixtures having different particle size combinations were hot-pressed after careful mixing.
The optical microscope images of the microstructures were processed by using an image analyzing
program; the binary morphology was chosen for characterizing the SiC particle distribution.
Computer Aided Measuring of Textile-Mechanical Parameters
Authors: Halász Marianna , Tamás Péter , Gräff József , Szabó Lajos
Published: March 2009

A new equipment for measuring the draping characteristics of static cloth is presented in
the paper. In contrast with Kawabata Evaluation System 3D geometrical data of the sample are
captured from photo images. Based on a mathematical reconstruction of geometry, and drape
coefficients and mechanical parameters are evaluated upon the geometrical model. The computer
controlled equipment moves a round table positioned in the centre providing the natural pleating of
fabric for the measuring. The core part of the equipment is a computer moved frame. The sample is
scanned by laser-beams. Lasers light the cross section curves of the sample on different levels.
There are four cameras on the frame taking the pictures of cross section curves in different levels.
3D geometry is reconstructed upon the pictures.
A mass, spring and damping element system is the basis of the cloth simulator. Springs are assumed
to be linear, while damps are proportional to the velocity. The physics engine running the simulator
calculates vertex positions at a time based on interaction forces with neighbouring vertices,
including stretch, bend and shear forces. Collision of the cloth model with the model of the
underlying object is performed and handled in each time step.
To evaluate the influence of the individual parameters, a series of simulations was performed. For
the real cloth samples, a range of cross-section curves is captured, digitalized and interpolated by
Fourier series. The same Fourier coefficients are determined for the cloth model as a function of
simulation parameters. The actual simulation parameters are defined by the minimum of the
difference between the modelled and the measured geometry.
On the Classification of 3D Periodic Polyhedral Cellular Systems
Authors: Réti Tamás , Bitay Enikő
Published: March 2009

In several fields of materials science space-filling polyhedral systems are generally used
for modeling and characterizing the microstructure of polycrystalline and cellular materials. In this
paper a simple quantitative method designated to classify 3D triply periodic, space-filling, cellular
systems is outlined. The concept of the proposed method is based on the known analogy between
the combinatorial structure of 3D space-filling polyhedral systems and of 4D polytopes. For
classification purposes various topological shape indices are defined and tested. It is demonstrated
that using two appropriately selected shape factors (asymmetry and compactness coefficients) a
global combinatorial classification of cellular systems can be performed.
On the Possible Mechanisms of Porosity Formation during Laser Melt Injection (LMI) Technology
Authors: Buza Gábor , Janó Viktória , Svéda Mária , Verezub Olga , Kálazi Zoltán , Kaptay György , Roósz András
Published: March 2009

In the present study the analysis of 5 different mechanisms of porosity formation during laser melt
injection (LMI) technology were performed. Experiments were supported by thermodynamic and
fluid-flow analysis. Special attention should be paid to i. clean the surface of the substrate, ii. use
inert shielding gas, iii. use proper particle size and gas velocity, iv. use proper laser power and laser
beam velocity to control bath temperature and v. deoxidize the surface of the added particles.
Dislocations in Silicon and D-Band Luminescence for Infrared Light Emitters
Authors: Kveder Vitaly V. , Kittler Martin
Published: March 2009

There is a growing demand for a silicon-based light emitters generating a light with a
wavelength in of 1.3-1.6 μm range, which can be integrated into silicon chips and used for in-chip
opto-electronic interconnects. Among other possibilities, the D1 luminescence at about 1.55 m,
caused by dislocations in Si, can be a suitable candidate for such in-chip light emitters. Here we
present a brief review of today knowledge about electronic properties of dislocations in silicon and
dislocation-related luminescence in connection with possible application of this luminescence for
silicon infrared light-emitting diodes (Si-LEDs).
Microstructure and Complex Magnetic Permeability of Ni0.3Zn0.7Fe2O4 Ferrite
Authors: Othéro de Brito Vera Lúcia , de Melo Francisco Cristóvão Lourenço , da Cunha Migliano Antônio Carlos
Published: March 2009

Ni-Zn ferrites are magnetic ceramics that are widely used in electric and electronic
components. Among Ni1-xZnxFe2O4 ferrites, Ni0.3Zn0.7Fe2O4 is known to be the one of highest
magnetic permeability in lower frequencies. This work is divided into two parts: the first part deals
with the influence of sintering temperature and forming conditions on the microstructure of
Ni0.3Zn0.7Fe2O4 ferrite. The second part deals with the influence of sintering temperature and
environmental variations of temperature on the complex magnetic permeability of such ferrite. The
ferrite studied in this work was fabricated by means of the conventional ceramic method. Complex
magnetic permeability between 100 kHz – 100 MHz is discussed in relation to sintering
temperature. The influence of environmental variations in temperature (-40 oC to +50 oC) on the
complex magnetic permeability of the ferrite sintered at 1300 oC is discussed.
Hydrogen Absorption-Desorption and Gamma-UMo Nuclear Fuel Powder Production
Authors: de Oliveira Fábio Branco Vaz , Riella Humberto Gracher
Published: March 2009

Gamma uranium-molybdenum alloys has been considered as the fuel phase in plate type
fuel elements for MTR reactors due to its performance under irradiation and metallurgical
processing. To its usage as dispersion phase in aluminum matrix, a necessary step is the conversion
of the as cast structure into powder, and the technique considered at IPEN / CNEN - Brazil was
HDH (hydration-dehydration). This work has the aim to study the hydrogen incorporation by
gamma-UMo alloys with 8% weight molybdenum. The samples were thermally treated under
constant flow of hydrogen, for temperatures varying from 500oC up to 600oC and times of 1 to 4
hours. Some of the curves relating mass incorporation and time for the above temperatures were
obtained, and the results related to its microstructures and ease of fragmentation.
An Alternative Fuel for Lime Industry: Evaluation the Pyrolysis of the Scrap Tires
Authors: Partata Andréia Ramos , Parreira Priciane Martins , Henrique Humberto Molinar , Avelar Carlos Eduardo Batista
Published: March 2009

Scrap tire is considered an environmental concern with inadequate final disposal. A good
alternative can be to use the tire as an energy source. Pyrolysis is a thermal process that can
transform the rubber portion of used tires into oil, gas and pyrolytic carbon. This type of carbon can
be converted into carbon black (CB). The lime industry that demands great amount of energy could
be one of the ways to take advantage the scrap tires adequately as energy source. This work aimed to
study the operational conditions of the pyrolysis process as well as investigating the possibility to
use the pyrolysis products from used tires as industrial fuel. A batch pilot-scale pyrolysis unit was
built. Temperatures from 400 to 600oC and relative pressures from 0 to -500 mmHg were
investigated in order to evaluate product distribution and quality. Experimental results showed that
as the reactor temperature was increased the pyrolytic carbon yield remained constant with a mean
of 39.8 wt % and the pyrolytic oil yield reached a maximum value of 45.1 wt % at 500 °C. It is also
possible to show that the pyrolytic oil can be used as liquid fuels because of its high heating value
(40-42 MJ/kg), excellent viscosity (1.6-3.7 cS), and reasonable sulfur content (0.97-1.54wt %). In
addition, chemical and physical characterization was made in order to compare the pyrolytic carbon
and oil with currently fuels used in Brazilian lime industries (wood charcoal and coke of
petroleum).
Study of the System Mo-Fe-B for Wear-Resistant Materials
Authors: Abenojar J. , Martinez M.A. , Velasco Francisco
Published: March 2009

Borides, especially transition metal borides, like Mo2FeB2 ternary boride, are promising
candidates for wear resistance applications. However, poor sinterability and extreme brittleness
raise difficulties to manufacture a structural material. In this work, the viability to obtain Fe-Mo-B
alloys with high wear resistance materials obtained by PM techniques is studied.
Other researchers use Cr and Ni alloyed steels and the B amount addition is very low. The main
objectives are to increase the amount of B, not to use Cr alloyed steels and to decrease the sintering
temperature. This can be obtained using mechanically alloyed Fe/B (50% by wt.) powders, which
are highly reactive after milling for 36 h.
The mixture has a composition of 40%Mo-40%Fe-20%Fe/B, being characterized by flow rate and
apparent density. These materials were uniaxially compacted and vacuum sintered. Specimens were
analysed by SEM and physical and mechanical properties were evaluated (density, dimensional
change, bending strength, hardness and wear).
Minimum Fluidization Velocity of Fine Particles
Authors: Cardoso Cássia Regina , Ataíde Carlos Henrique , Abreu J.M.
Published: March 2009

The minimum fluidization velocity is an important parameter in the design and operation
of an industrial unit of fluidization. In the present work the minimum fluidization velocities of fine
particles were obtained through two experimental methodologies. The first one is the classic
procedure to determine that parameter analyzing the diagram of medium pressure drop in the bed in
function of the superficial gas velocity, during the defluidization of the bed. And the second is the
technique of identifying the minimum fluidization velocity interpreting the behavior of the
normalized standard deviation of the pressure drop in the bed. A cylindrical bed of transparent
acrylic was used in the process and the used particles were glass spheres, FCC and zinc powder. To
compare the precision of the two methodologies some equations that predict the minimum
fluidization velocity were used.
Influence of Nb2O5 on the Electrical Properties of Porous ZrO2-TiO2 Ceramic Used as Soil Humidity Sensor for Environmental Monitoring
Authors: Oliveira Rodrigo de Matos , Nono Maria do Carmo de Andrade , Britto Filho G.P.
Published: March 2009

The soil humidity sensor plays fundamental role in the monitoring of hazard areas with
landflows and landslides, about which in Brazil stories exist since 1671. Nowadays, it is just known
that the majority of the mass movements in the hillsides occur in rainy periods, what makes the
water the most important deflagrator agent of these movements, decreasing the soil resistance,
increasing its specific weight and increasing the internal pressures as well. In this direction, the
sensing elements developed by Group SUCERA/LAS/INPE uses the advantages presented for
ceramics, in particular metal oxides, in terms of their mechanical strength, their resistance to
chemical attack and their thermal and physical stability. In this work the results of the
characterization analyses of sensor elements of ZrO2-TiO2 doped with 1, 5, 10, 15 e 20 % Nb2O5
porous ceramic, sintered at 1200 °C are shown and discussed.
X-Ray Diffraction Analysis and Magnetic Properties of Pr-Fe-B HDDR Powders and Magnets
Authors: Silva S.C. , Duvaizem José Hélio , Martinez Luís Gallego , Orlando M.T.D. , de Faria Jr. Rubens Nunes , Takiishi Hidetoshi
Published: March 2009

Fine magnetic powder has been produced using the hydrogenation
disproportionation desorption and recombination (HDDR) process. The first goal of this work
involved an investigation of a range of disproportionation/desorption temperatures between
800 and 900°C with the purpose of optimizing the HDDR treatment for a Pr14Fe80B6 alloy.
The cast alloy was annealed at 1100°C for 20 hours for homogenization. The optimum
disproportionation temperature for achieving high anisotropy was 820°C. The influence of the
reaction temperature on the microstructure and magnetic properties of Pr14Fe80B6 HDDR
powders and magnets has been shown. A second stage of this study involved the
characterization, for each temperature, of the HDDR processed powder using X-ray
diffraction analysis. Samples of the HDDR material have been studied by synchrotron
radiation powder diffraction using the Rietveld method for cell refinement, phase
quantification and crystallite sizes determination. Scanning electron microscopy (SEM) has
also been employed to reveal the morphology of the HDDR powder.
Compaction Behaviour of Yttria-Zirconia Powders Obtained from Micro and Nanoparticles Mixtures
Authors: Mineiro Sergio Luiz , Nono Maria do Carmo de Andrade
Published: March 2009

The densification behavior of mixtures of nanocrystalline and conventional
microcrystalline zirconia powders undergoing uniaxial pressing was investigated. The mixtures
were obtained with ratios between 10 and 80 wt.% of nanoparticulate powder added to the
microparticulate powder. Nitrogen and Mercury porosimetry were used to measure the pore size
distributions of the compacts. The powders and the fracture surfaces of the compacts were observed
via SEM. The results showed that compacts of the powder mixtures attain higher densities during
pressing than the unmixed powders. The powder mixture with 80 wt. % of nanoparticles showed the
better particle packing efficiency. A comparison between density values of uniaxial and isostatic
pressing also was done and indicated that the best results were obtained by the isostatic method.
Effect of Different Solid Amounts in the Physical and Microscopical Properties of SiC Porous Ceramics
Authors: Santana Jerusa Góes Aragão , Minatti José Luiz , de Campos Élson , de Melo Francisco Cristóvão Lourenço , Kajita Tetunori
Published: March 2009

The presence of pores in ceramics is directly related to the chosen forming process. So, in
the starch consolidation method, the ceramics show, after burning, pores with morphology similar
to that presented by this organic material. On the other hand, the increase in solid load leads up to
alterations in dispersion viscosity, increasing the thermal stresses during drying and sintering
processes. In order to verify the solid percentage influence in ceramic final properties, samples were
prepared with silicon carbide in different compositions using or not starch as binder agent and pore
forming element. The characterization of the ceramic pieces was performed by superficial
roughness measurements, porosity besides by optical and scanning electron microscopy. The results
showed ceramics with SiC and starch presented physical and microscopic properties slightly higher
in relation to those with only ceramic powder in their composition. The presence of organic
material, agglomerated and foam during the forming were essential for the final properties of the
studied samples.
Synthesis of Silicon Nitride Using Taguchi Planning Methodology
Authors: Richetto Katia C.S. , Silva Cosme Roberto Moreira
Published: March 2009

Silicon Nitride is considered as an important material for use in structural applications.
Its performance is severely influenced by modern synthesis processes. In the present work, silicon
nitride powder synthesis was performed using liquid silicon tetrachloride and gaseous ammonia, at
low temperature and inert atmosphere. Diimide pyrolisis was made on temperature between 1300
and 1500 0C. A Taguchi design of experiments methodology was applied, aiming to obtain powders
with appropriated characteristics for structural applications. On pyrolisis, the use of alumina based
substrates resulted on SIALON phase formation, probably originated from oxygen reaction,
provided from alumina. Silicon carbide substrates and alumina recovered with silicon nitride
enhance synthesis of pure silicon nitride powder.
Optimization of the Production of Quicklime by Calcination in Rotary Kilns
Authors: Soares Bruno D. , Hori Carla Eponina , Batista Carlos E.A. , Henrique Humberto Molinar
Published: March 2009

It well known that the operational conditions of rotary kilns affect strongly the quality of
quicklime produced. This work presents a study about parametric optimization of rotary kilns for
quicklime production (CaO) from thermal decomposition of calcite limestone (CaCO3). The
approach used is based on the technique of design of experiments (DOE) to identify the most
significant variables which affect the quality of oxide and, in addition, to determine better
conditions of production. An experimental setup in laboratory scale was build in order to carry out
the experiments. Calcination temperature, calcination time, rotation speed, particle mean diameter,
heat flow and air flow rate were evaluate using a fractional factorial design. The parametric
optimization shows that the raise of time and temperature of calcinations produces an increase of
free CaO terms. However this operation is not useful due to sintering process observed in the BET
surface area results. A correlation between quicklime reactivity and specific surface area could be
established, in way that reactive quicklimes presented bigger areas. Finally, it was possible to
determine the best conditions of quicklime production and to estimate a quadratic model by using a
central composite design and a like surface response model. It was found that the best region of
operation is about 900oC and 45 minutes of calcination time.
A Technology of Using Surface Magnetization Variations for Evaluating the Wear-Resistant Properties of the Die Surfaces with Different TiN Films
Authors: Chang Yuh Ping , Wang Kuo Hsing , Lin Chao Hsien , Liu Chien Te , Hwang Yih Chyun
Published: March 2009

Generally speaking, the major parameter which has been used to monitor the dynamic
tribological properties of the films over the past decades is friction coefficient. However, it has
shown low in sensitivity for many cases. Therefore, it is necessary to introduce more improved
physical measurements other than the friction coefficient to monitor and control the film
tribological characteristics in sliding contacts. In view of this, the novel technology of using instead
surface magnetization variations for evaluating the wear-resistant properties of the films is
proposed. The experiment was conducted by the pairs of SUS304 rubbing with SKD11 substrate
with different TiN films (PVD and CVD) on the surface at different normal loads in dry friction
process. According to the experimental results of the dynamic variations of surface magnetization
and friction coefficient with the SEM observations of the wear tracks, the effects of normal loads on
the friction and wear properties for the die surfaces with different TiN films can be investigated.
The experimental results show that the continuous surface magnetization variations can be used to
determine the timing of film fracture and the endurance life more accurately than that by the friction
coefficient variations as usual. Therefore, the novel method of using surface magnetization
variations does show great potentialities for evaluating the tribological properties of the die surfaces
with different TiN films.
The Swashplate Angle Control of a Variable Displacement Pump with an Electro-Hydraulic Proportional Valve
Authors: Chu Ming Hwei , Kang Yuan , Chen Yi Wei , Chang Yeon Pun
Published: March 2009

In this paper, the mathematic model of the swashplate type variable displacement axial
piston pump (VDAPP) is established. The VDAPP applied to an electro-hydraulic servo control
system usually induces unstable performance, so that a servo controller is designed and analyzed to
control the swashplate angular displacement and improve the stability and transient response of pump
performance. The flow and pressure variations of pump with the proposed controller are investigated
and analyzed by mathematic simulations and experiments. The simulation and experiment results
show that the proposed controller can improve the stability of swashplate angular displacement, and
easily applied to the energy saving hydraulic systems.
Opto-Mechatronics Integration for Metrology
Authors: Lin Jium Ming , Chang Po Kuang
Published: March 2009

This paper integrated multi-domain knowledge of electronics, optics, control as well as
precision measurement, and proposing a high resolution subdividing electronics module to the
sinusoidal encoder output of a positioning motor, such that the module can not only be used as a
counter for linear and/or angular measurements, but also subdivide the periods of the sinusoidal
encoder signals up to 1600 times. From the results of experiment test it can be seen that the whole
module is suitable for those applications requiring high-resolution encoder, nanometer measurement
as well as fast data acquisition with phase tolerance of ± 45°.
The 3D Printer Design and Model Formation by a Commercial Inkjet Printing Module
Authors: Cheng Chun I , Chen Chun Hao , Lai Wei Hsiang , Hwang Sheng Jye , Lee Sen Yung
Published: March 2009

This research utilizes a 2D printer mechanism from a commercial available inkjet printer,
combines with hardware and software to build up a new concept 3D printer. This 3D printer can
receive printing information from personal computer, and setting the required layer thickness to
stack those layers into a solid model. The largest build volume is 300x420x350 mm, print head
resolution is as high as 1200x2400 dpi, and the life of printer head is longer than 12 weeks which is
far longer than 4 weeks of Z Corp’s. There are many specifications are better than or equivalent to
those of Z Corp’s Z-510 which is the state-of-art machine of this powder based rapid prototyping.
A Finite Element Investigation into the Changing Channel Angular Extrusion of Brass Alloy
Authors: Chen Dyi Cheng , Wang Jia Ci , Tzou Gow Yi
Published: March 2009

This study investigates a novel changing channel angular (CCA) extrusion process, in
which high strains are induced within the billet by passing it through a series of channels of unequal
cross-sections arranged such that they form specified internal angles. Using commercial
DEFORMTM 2D rigid-plastic finite element code, the plastic deformation behavior of CuZn37 brass
alloy is examined during one-turn and two-turn CCA extrusion processing in dies with internal
angles of φ =90o, 120o, 135o or 150o, respectively. The simulations focus specifically on the effects
of the processing conditions on the effective strain, the rotation angle and the effective stress
induced within the extruded billet. The numerical results provide valuable insights into the shear
plastic deformation behavior of CuZn37 brass alloy during the CCA extrusion process.
Degradation of Yttria Stabilized Zirconia Thermal Barrier Coatings by Molten CMAS (CaO-MgO-Al2O3-SiO2) Deposits
Authors: Mohan Prabhakar , Yuan Biao , Patterson Travis , Desai Vimal , Sohn Yong Ho
Published: March 2009

In advanced gas turbine engines that operate in a dust-laden environment causing
ingestion of siliceous debris into engines, thermal barrier coatings (TBCs) are highly susceptible to
degradation by molten CMAS (calcium-magnesium alumino silicate) deposits. In this study, the
degradation mechanisms other than the commonly reported thermomechanical damage are
investigated with an emphasis on the thermochemical aspects of molten CMAS induced degradation
of TBCs. Free-standing yttria stabilized zirconia (8YSZ) TBC specimens in contact with a model
CMAS composition were subjected to isothermal heat treatment in air at temperatures ranging from
1200°C to 1350°C. Phase transformations and microstructural development were examined by
using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy.
Starting at 1250°C, the molten CMAS readily infiltrated and dissolved the YSZ coating followed by
reprecipitation of zirconia with a different morphology and composition that depends on the local
melt chemistry. Significant amount of Y2O3 depleted monoclinic ZrO2 phase evolved from CMAS
melt that dissolved ť-ZrO2 was evident. Thus the mechanism of dissolution and reprecipitation due
to molten CMAS damage resulted in destabilization of the YSZ with disruptive phase
transformation (t’ f + m).
Corrosion in Biomass Combustion Systems
Authors: Coleman K.E. , Simms N.J. , Kilgallon P.J. , Oakey J.E.
Published: March 2009

There is growing concern over the effects of global warning. In response the power
generation sector is having to consider a wider range of systems and fuels for use in generating heat
and power. One of the classes of solid fuels that is being increasingly developed is biomass, which
is regarded a both sustainable and carbon neutral. In fact, the term biomass covers a wide range of
fuels from waste products, such as straw, forestry wastes and sawdust, through to purpose grown
energy crops, such as coppiced willow and miscanthus.
To maximise combustion plant efficiency it is necessary to use high temperature/pressure steam
turbines. However, to generate such steam conditions, the high heat exchanger surface temperatures
can interaction with the various potential products of biomass combustion to cause excessive
deposition and corrosion of these surfaces. This paper considers the range of heat exchanger
operating environments that can be produced by the combustion of different potential biomass fuels,
especially the effects of the higher K and Cl contents of the faster growing biomass fuels.
This paper reports the results of a series of laboratory corrosion tests that have been carried out to
assess the effects of various types of biomass on the corrosion of high temperature heat exchanger
materials in combustion plants. The corrosion tests have been carried out using the deposit recoat
method in controlled atmosphere furnaces. Six 1000 hour tests have been carried out at typical
superheater / reheater and evaporator conditions (450-600°C) using simulated deposit and gas
compositions, which have been selected on the basis of potential biomass fuel compositions. The
five metals exposed in this study are widely used in power plant heat exchangers: 1% Cr steel,
2.25% Cr steel (T23), 9% Cr steel (T91), X20CrMoV121, TP347HFG and alloy 625.
During the course of the tests, the material degradation was monitored using traditional mass
change measurements. In order to produce statistically valid data on the actual metal loss from the
materials, the performance of the materials in these tests was determined from dimensional
metrology before and after exposure: pre-exposure measurements were made using a micrometer;
post-exposure measurements were made using an image analyser system. SEM/EDX and XRD
analyses have been used to confirm corrosion mechanisms and their association with corrosion
damage levels. For each material, the dimensional metrology data have been used to determine the
sensitivity of the corrosion damage to changes in the exposure conditions (e.g. deposit composition,
gas composition) to generate models of the corrosion performance of the materials. The corrosion
data and model outputs have been compared with data available from power plants operating on
coal, straw or wood fuels.
Characterization of the Oxide Films Formed at the Surface of Ni-Base Alloys in Pressurized Water Reactors Primary Coolant by Transmission Electron Microscopy
Authors: Sennour Mohamed , Marchetti Loïc , Perrin Stéphane , Molins Régine , Pijolat Michèle , Raquet Olivier
Published: March 2009

The oxide film formed on nickel-based alloys in Pressurized Water Reactors (PWR)
primary coolant conditions (325°C, aqueous media) has been investigated by Transmission Electron
Microscopy (TEM). TEM observations revealed an oxide layer divided in two parts. The internal
layer was mainly composed of a continuous spinel layer, identified as a mixed iron and nickel
chromite (Ni(1-x)FexCr2O4). Moreover, nodules of Cr2O3 were present at the interface between this
spinel and the alloy. The external layer is composed of large crystallites corresponding to a spinel
structure rich in iron (Ni(1-z)Fe(2+z)O4) resulting from precipitation phenomena. The influence of
alloy surface defects was also studied underlining two main consequences on the formation of the
passive film e.g. the internal layer. On one hand, the growth kinetics of the internal spinel rich in
chromium increased with the surface defect density. Besides that, when the defect density
increased, the oxide scale became more finely crystallized. This result agrees with a growth
mechanism due to a rate limiting process of diffusion through the grain boundaries of the oxide. On
the other hand, the quantity of Cr2O3 nodules increased with the number of surface defects,
revealing that the nodules nucleated preferentially at defect location.
Oxidation Behavior of Wrought Gamma-Prime Strengthened Alloys
Authors: Pike Lee M. , Srivastava S.K.
Published: March 2009

Oxidation testing of four gamma-prime (γ') strengthened alloys used extensively in aero
and/or land-based gas turbine engines was performed. The studied alloys, which included R-41
alloy, Waspaloy alloy, 263 alloy and the new HAYNES® 282® alloy were selected because they
belong to a family of alloys distinguished by their possession of sufficient fabricability to be
produced in sheet or plate form. The test program included both static and dynamic oxidation
testing. The static oxidation tests were performed in flowing air at temperatures of 871, 927 and
982°C (1600, 1700, and 1800°F). The dynamic (burner rig) oxidation tests were performed at
871°C (1600°F). The results of these test programs will be presented.
Thermal Alumina Scales on FeCrAl: Characterization and Growth Mechanism
Authors: Chevalier Sébastien , Galerie Alain , Heintz Olivier , Chassagnon Remi , Crisci Alexandre
Published: March 2009

High temperature oxidation resistance of alumina-forming materials is connected to the
growth of dense, stable and protective alumina scales. Depending on temperature, impurities
present in the base alloys, presence of water vapour in the oxidizing atmosphere, the alumina scales
are composed of alpha-alumina (which is the stable phase obtained for temperatures over 1000°C)
or of transient alumina (γ,θ,δ obtained for lower temperatures). It is generally considered that γ-
Al2O3 grows when T<850°C, that θ-Al2O3 is present for 850°C<T<1000°C and that α-Al2O3 is
stable when T exceeds 1000°C.
The exact role played by transient alumina formation and/or transformation on the high temperature
performances of alumina-forming materials is not exactly defined. Many works proposed that
transient alumina phases grew during the first steps of the oxidation process and transformed into
the stable phase after further oxidation. The transformation of transient phases in the stable alphaphase
is generally accompanied by a volume contraction of around 14 %.
In order to get better oxidation resistance, the formation of transient alumina is not wished, because:
1) their growth rate is generally higher than that of alpha-alumina with, as a consequence, a huge Al
consumption, detrimental for the material resistance after long exposures, 2) the change in volume
during the transformation of transient phases into alpha-alumina can generate stresses in the oxide
scale and can weaken its adherence to the underlying substrate, leading to massive spallation.
The present study deals with the coupling of different characterization tools in order to precisely
identify the transient phases grown on FeCrAl materials. The use of scanning electron microscope
(SEM-FEG), transmission electron microscope (TEM), Photoluminscescence Spectroscopy(PLS),
X-ray photoelectron spectrometry (XPS) and X-ray diffraction at different glancing angles (XRD)
on model materials oxidized at two temperatures (850 and 1100°C) could help the identification of
transient phases. These techniques gave a better understanding of the alumina scale growth
mechanism.
Microwave Switches and Modulators Based on 4H-SiC p-i-n Diodes
Authors: Zekentes Konstantinos , Basanets Volodymyr V. , Boltovets Mykola S. , Kryvutsa Valentyn A. , Orechovskij Volodymyr O. , Simonchuk Vasyl I. , Zorenko Alexander V. , Romanov Leonid P. , Kirillov Aleksey V. , Bano Edwige , Camara Nicolas
Published: March 2009

Multi-diode broadband microwave signal modulators based on 4H-SiC p-i-n diodes were
fabricated and fully characterized. The three-diode modulators are characterized by a transmission
loss of 1-2 dB and isolation of 27-34 dB in the 2-7 GHz frequency range. Two-diode modulators were
specially designed for high-temperature operation. These modulators are characterized by a
transmission loss of 1.1-2.6 dB and isolation of 33-44.5 dB, in the 2-7 GHz frequency range at
temperatures up to 300°C.
Numerical Evaluation of Forward Voltage in SiC Pin Diode with Non-Ohmic Current Component in Contact to p-Type Layer
Authors: Ohtsuka Kenichi , Tarui Yoichiro , Watanabe Tomokatsu , Fujihira Keiko , Matsuno Yoshinori
Published: March 2009

Forward voltage of SiC pin diodes is evaluated by device simulation, where a p-type
contact is described by Schottky barrier to a p-type surface region. The contact resistance is calculated
from the comparison to I-V characteristic of Schottky structure to a p-SiC layer with a sufficiently low
Schottky barrier height. Even in the relatively low contact resistance rc of 10-4 Wcm2, non-ohmic
current component is observed in Schottky structure to p-SiC and the increase of forward voltage of
pin diodes is fairly small. Forward voltage of pin diodes increases in the pin diodes with contact
resistance rc over 10-4 Wcm2. The same behavior is also observed irrespective of a time constant of
carriers, and doping concentration and thickness of a drift layer.
Switching Performance of Epitaxially Grown Normally-Off 4H-SiC JFET
Authors: Malhan Rajesh Kumar , Rashid S.J. , Kataoka Mitsuhiro , Takeuchi Yuuichi , Sugiyama Naohiro , Udrea F. , Amaratunga G.A.J. , Reimann T.
Published: March 2009

Static and dynamic behavior of the epitaxially grown dual gate trench 4H-SiC junction
field effect transistor (JFET) is investigated. Typical on-state resistance Ron was 6 – 10mΩcm2 at VGS
= 2.5V and the breakdown voltage between the range of 1.5 – 1.8kV was realized at VGS = −5V for
normally-off like JFETs. It was found that the turn-on energy delivers the biggest part of the switching
losses. The dependence of switching losses from gate resistor is nearly linear, suggesting that
changing the gate resistor, a way similar to Si-IGBT technology, can easily control di/dt and dv/dt.
Turn-on losses at 200°C are lower compared to those at 25°C, which indicates the influence of the
high internal p-type gate layer resistance. Inductive switching numerical analysis suggested the strong
influence of channel doping conditions on the turn-on switching performance. The fast switching
normally-off JFET devices require heavily doped narrow JFET channel design.
1270V, 1.21mΩ·cm2 SiC Buried Gate Static Induction Transistors (SiC-BGSITs)
Authors: Tanaka Yasunori , Yano Koji , Okamoto Mitsuo , Takatsuka Akio , Arai Kazuo , Yatsuo Tsutomu
Published: March 2009

We have succeeded to fabricate SiC buried gate static induction transistors (BGSITs) with
the breakdown voltage VBR of 1270 V at the gate voltage VGS of –12 V and the specific on-resistance
RonS of 1.21 mΩ·cm2 at VGS = 2.5 V. The turn-off behaviors of BGSITs strongly depend on the source
length WS, which is the distance between the gate electrodes. The rise time tr of BGSIT for WS = 1,070
μm is 395 nsec, while that for WS = 210 μm is 70nsec. From the 3D computer simulations, we
confirmed that the difference in turn-off behavior came from the time delay in potential barrier
formation in channel region because of high p+ gate resistivity. The turn-off behaviors also depend on
the operation temperature, especially for long WS. On the other hand, the turn-on behaviors hardly
depend on the WS and temperature.
Three Dimensional Analysis of Turnoff Operation of SiC Buried Gate Static Induction Transistors (BG-SITs)
Authors: Yano Koji , Tanaka Yasunori , Yatsuo Tsutomu , Takatsuka Akio , Okamoto Mitsuo , Arai Kazuo
Published: March 2009

The turnoff mechanism of SiC buried gate static induction transistors (SiC-BGSITs) were
analyzed by three dimensional device simulation. A current crowding occurs in the portion near the
channel center away from the gate contact during the initial phase of the turnoff operation, which is
resulted from a non-uniform potential distribution through the gate finger with the displacement
current flowing there. This increases the turnoff delay time. The impact of source length on the turnoff
performance was made clear.
RF Characteristics of a Fully Ion-Implanted MESFET with Highly Doped Thin Channel Layer on a Bulk Semi-Insulating 4H-SiC Substrate.
Authors: Katakami S. , Ono Shuichi , Arai Manabu
Published: March 2009

We fabricated a 0.5-μm-gate MESFET on a bulk 4H-SiC semi-insulating substrate using
ion implantation for the channel and contact regions. Our device design used a thin, highly doped
channel layer, which was implanted at single energy to improve the device’s RF characteristics. The
electrical characteristics of the ion-implanted MESFET annealed at 1700°C were better than those of
the ion-implanted MESFET annealed at 1300°C. The fabricated ion-implanted MESFET has a
maximum transconductance of 32.8 mS/mm and an fT/fmax of 9.1/26.2 GHz. The saturated output
power was 26.2 dBm (2.1 W/mm) at 2 GHz. These values were the same as those of the conventional
epitaxial MESFET with a recessed gate.
Normally-Off 4H-SiC Power MOSFET with Submicron Gate
Authors: Yamashita Kenya , Egashira Kyoko , Hashimoto Koichi , Takahashi Kunimasa , Kusumoto Osamu , Utsunomiya Kazuya , Hayashi Masashi , Uchida Masao , Kudo Chiaki , Kitabatake Makoto , Hashimoto Shin
Published: March 2009

In order for SiC-MOSFET to be practical in various power electronics applications, low
specific on-resistance Ron,sp, high breakdown voltage and “normally-off” characteristics have to be
fulfilled even at high temperature. We fabricated a SiC-MOSFET employing a submicron gate with
channel length Lg of 0.5μm by a self-aligned implantation and aδ-doped epitaxial channel layer to
successfully demonstrate the following features. The normally-off characteristics was confirmed
from room temperature to 200°C where the therethold voltages Vth were 2.9V at room temperature
and 1.6V at 200°C, respectively. The Ron,sp were 4.6mΩcm2 at room temperature and 9.2mΩcm2 at
200°C, respectively, while the breakdown voltage was greater than 1400V .