bluuebunny/crossref_metadata_2025 huggingface dataset:
Bioactive Grain Refined Magnesium by Friction Stir Processing
Authors: Ratna Sunil B. , Sampath Kumar T.S. , Uday Chakkingal
Published: February 2012

Magnesium and its alloys are promising candidates for temporary implant applications due to their combination of mechanical properties, biocompatibility and biodegradation. But higher degradation rate restricts their wider applications. Recently friction stir processing (FSP) has emerged as a promising tool to attain near surface fine grain structure in materials. In the present work commercial purity magnesium was processed by FSP to obtain fine grain structure and the effect of the grain refinement on the bioactivity was investigated. The microstructural observations were carried out at different locations of the processed regions, from an original grain size of 1500μm, grain refinement was achieved to a level of 6.2μm at the nugget zone. Microhardness was measured across the processed regions and improvement was observed at the nugget zone. Contact angle measurements were carried out to estimate the wettability of the material and the measurements indicate increased wettability due to the increased surface energy induced by grain refinement. For studying the bioactivity the FSPed samples were immersed in simulated body fluids (SBF 5X) for different intervals of time. The phases formed on the samples were investigated by X-ray diffraction (XRD) method, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The phases on the samples after 72hr of immersion were confirmed as magnesium hydroxide, hydroxyapatite and magnesium phosphate by XRD. Controlled degradation due to formation of these phases was observed. FSPed samples have more deposition of Ca/P than non FSP samples which implies better control over the degradation. Hence grain refinement by FSP can be a simple technique to control the degradation of magnesium for temporary implant applications.
Quantitative Non-Destructive Evaluation of Steel Microstructure Using Elastic Wave Perturbation
Authors: Mishra Brajendra , Kiattisaksri Peerapong , Poncelow Jonathan , Olson David L.
Published: February 2012

The purpose of this investigation is to develop the nondestructive tools for microstructure assessments in carbon alloyed steels. The role of carbon in steel and its effects on electromagnetic property and also the free electron model have been reviewed. The fundamental electromagnetic principle behind low frequency impedance measurements has been included. The systematic analysis of phonon vibration and ultrasonic resonance spectroscopy for elastic wave perturbation in T22 Cr-Mo steel has been presented. A brief examination of nondestructive microstructure evaluation techniques has been described. The induced microstructure variations in Grade T22 Cr-Mo steel, including the correlations of changes in physical (microstructure) and mechanical (hardness data) properties during annealing have been measured. The explanations of aged carbide precipitates, martensitic and pearlitic nucleation and growth have been illustrated. The possibility of simultaneous use of two nondestructive wave techniques is discussed. The electron model and electron interactions are associated and are shown to support the results of low frequency impedance measurements enhanced elastic wave perturbations.
Effect of 10 at.% Nb Addition on Sintering and High Temperature Oxidation of W0.5Cr0.5 Alloy
Authors: Telu Suresh , Karthik Vaduganathan , Mitra Rahul , Pabi Shyamal Kumar
Published: February 2012

The effect of 10 at.% Nb on the sintering and high temperature oxidation behavior of W0.5Cr0.5alloy was investigated. Elemental powder blends were made nanostructured by high energy mechanical milling, compacted and finally sintered under reduced atmosphere at 1790°C. The sintered samples were subjected to cyclic isothermal oxidation tests at 800°C to 1200°C in air. The experimental results shows superior sinterability and oxidation protection of W0.5Cr0.5alloy compared to pure W. Characterization of the oxide scales shows porous external W-rich oxide (WO3) formation which is not ideally suitable for oxidation resistance. On the other hand, W-Cr alloy with 10 at.% Nb shows the remarkable sinter densification (~98%) and oxidation resistance up to 1200°C. The oxide scale of the ternary alloy shows formation of stable Cr2O3, Nb2O5oxides and/or complex Cr-Nb oxide (CrNbO4), and there was no evidence of WO3formation in this case.
Spark Plasma Sintering of Fe-Cr-Mo-P-B-C-Si Amorphous Alloy
Authors: Ravi K.R. , Indumathi  , Subramanian R. , Murty B.S.
Published: February 2012

In the present work, synthesis of bulk Fe amorphous alloy by mechanical alloying of 70Fe-15Cr-4Mo-5P-4B-1C-1Si powders followed by consolidation of powders using Spark Plasma Sintering process is reported. The evolution of phase, microstructure, relative density and hardness of amorphous alloy as a function of spark plasma sintering temperature is discussed. Transmission electron microscopy investigation has shown partial divitrification of amorphous matrix into nanocrystalline phase during spark plasma sintering of amorphous Fe alloy. The hardness of amorphous alloy sintered at 525 – 575°C are in the range of 675 - 725 MPa.
Wear Characteristic of Al-Based Metal Matrix Composites Used for Heavy Duty Brake Pad Applications
Authors: Asif Mohammad , Chandra Kamlesh , Misra Prabhu Shankar
Published: February 2012

Wear study of metal matrix composites used as friction material is one of the most important parameter for determining the brake performance. The present investigations relates to the development of Aluminum powder based brake pads; where the back plates are also made of Aluminum based powders respectively. Thus it is aimed to fabricate net-shape Aluminium powder based brake pads in a single forming operation with better characteristics (low wear, low temperature rise, stable coefficient of friction) employing a newly developed technology namely “Hot Powder Preform Forging” technique. Three Aluminum based friction composites which are designated as ALM 01, ALM 02 & ALM 03 were formulated. The dry wear test is carried out using a pin-on-disc tribo-tester at constant sliding speed of 9 ms-1 under a load of 50 N. The counter face disc is made of heat treated grey cast iron. During the test, the cumulative wear (gm), Coefficient of friction, temperature rise (oC) and noise level (dB) were recorded. The effect of load at constant speed on sliding wear, frictional characteristic of aluminum based MMC (rotor / drum) in dry condition is studied. On the basis of initial laboratory tests like density, Hardness, wear test, the samples were qualified for sub-scale dynamometer test at Rejected Take Off condition. Optical microscope was used to investigate the microstructure of metal matrix friction composites surfaces. The results revealed that coefficient of friction was more stable. The Cumulative wear (gm) was low with rise in temperature. It was also observed that distribution of ingredients in matrix was fine and homogeneous.
Effect of Cold Working on the Mechanical Properties of a Medium Carbon Low Alloy Steel
Authors: Kumar R. Suresh , Jha Abhay Kumar , Sreekumar K. , Sinha Parameshwar Prasad
Published: February 2012

Missile and rocket motor cases are often fabricated by welding process. The replacement of welded hardware with the flow formed construction eliminates many problems associated with welded joints. Data on the cold workability of the material in different heat treatment conditions is essential for the flow forming of the material. The cold workability of a 0.3C-CrMoV grain refined steel processed by air melting and electroslag refining was studied in annealed and Q&T conditions through cold rolling process. The effect of heat treatment on the strength properties of the rolled materials was also studied. The observed behaviour is explained in the light of the results of the microstructural characterization.
Local Deformation Behavior of Inconel 718 TIG Weldment at Room Temperature and at 550°C
Authors: Sudarshan Rao G. , Saravanan K. , Harikrishnan G , Sharma V.M.J. , Ramesh Narayanan P. , Sreekumar K. , Sinha Parameshwar Prasad
Published: February 2012

The weld portion will have different mechanical properties in weld bead, HAZ and fusion boundary due to variation in the microstructure, chemistry and internal stresses that arise in the welding process. Inconel 718 TIG welded samples are tested to study the deformation behavior of the weld constituents with the help of non contact laser extensometer. Stress-strain curves for the individual constituents of weld, parent, fusion boundary and HAZ are evaluated at room temperature and at 550°C. Test results show that the welded samples exhibited 50% lower tensile properties compared to the parent material. Parent metal remains elastic through out the test. The proof stress of the weld alone is 100 MPa lower than the average proof stress of the welded sample when considered standard gauge length.
Effect of Ultrasonic Treatment on the Grain Refinement and Mechanical Properties of AZ91 Magnesium Alloy
Authors: Bhingole Pramod , Chaudhari Gajanan
Published: February 2012

The present study examines the microstructural evolution and mechanical properties of AZ91 magnesium alloy solidified under high intensity ultrasonic treatment (UST). High intensity ultrasonic vibrations were introduced isothermally below the liquidus temperature into the solidifying AZ91 alloy for the refinement of primary α-Mg grains and β-Mg17Al12intermetallic phase.Various microstructures were produced using different intensity of ultrasonic vibration at a constant temperature and fixed duration of UST. Without any ultrasonic treatment, the structure contains dendrites of primary α-Mg phase which are coarser and non-uniform in size. Nearly uniform, equiaxed grains with continuous and uniform network of intermetallic phase segregated along the grain boundaries were obtained in alloy subjected to high intensity ultrasonic vibration. The average grain size in this case decreased drastically from 300 μm for (without UST) to 17 μm (with UST at intensity of 4 kW/cm2). Vickers hardness also increased steadily with increase in ultrasonic intensity. The mechanisms for microstructural refinement are discussed and it is concluded that the fine uniform grain structure achieved under ultrasonic vibrations is attributed to the cavitation and the acoustic flow induced by ultrasonic vibrations.
Optimization of Hot Rolling and Annealing Process of Low Ni Stainless Steel Using Simulation Studies
Authors: Kumar Vinod , Sarvanan D. , Kumar Santosh , Saxena Atul , Sisodia S. , Jha B.K.
Published: February 2012

Processing of low Ni Stainless Steel poses a serious problem during rolling both in roughing and finishing stands owing to high load. This is primarily attributed to high work hardening rate due to low Ni and high Mn in such steels. An increase in temperature to bring down the rolling load deteriorates the surface quality. In addition to this, high hardness in the cold rolled and annealed product posses problem during further forming operation. To overcome these problems, simulation studies were carried out using Gleeble Thermo-mechanical Simulator (i) to determine flow stress under different hot rolling conditions and (ii) to simulate continuous strip annealing process to optimize annealing parameters to bring down the hardness. It was observed that the flow stress increases gradually with a decrease in temperature till 1050C and thereafter, at a significantly high rate. It was further observed that continuous dynamic recovery occurred at 1050 – 1150C which gradually diminished and resulted in work hardening at lower temperatures. In view of this, rolling schedule was modified which led to smooth rolling without any over-load problem. It was also found based on simulation studies that the hardness was minimum in the temperature range of 950-975 C, however, no/ little recrystallisation occurred at these temperatures. A fully recrystallised grain with significant drop in hardness was observed at 1050C. Annealing cycle was accordingly modified for regular commercial production which has given good result.
Selection and Design Principles of Wrought Aluminium Alloys for Structural Applications
Authors: Mukhopadhyay A.K.
Published: February 2012

This article discusses the fundamental principles associated with the selection of aluminium alloys for specific purposes, alloy design & heat treatment procedures and development of key microstructures responsible for obtaining desired properties in selected wrought Al alloys for aerospace and defence applications. Influence of micro/trace additions of suitable alloying elements on the microstructure and properties of high strength 7xxx series Al alloys is further highlighted.
Influence of Crystallographic Texture on Mechanical Properties in Cold Rolled 7XXX Series Al Alloys Used in Space Applications
Authors: Ramesh Narayanan P. , Suwas Satyam , Sreekumar K. , Sinha Parameshwar Prasad , Ranganathan Srinivasa
Published: February 2012

This paper covers the influence of crystallographic texture on the mechanical properties in two of the most important high strength Al-Zn-Mg family of aluminium alloys, viz., AA7075 and AFNOR7020 alloys, used in the Aerospace industry. AFNOR7020 Alloy developed a stronger texture compared to the other two alloys. S component of texture is stronger in AA7075 alloy whereas the Bs component is stronger in AFNOR7020 alloy. This is attributed to the shear banding which was found absent in the other alloy. The starting material, AA7075 in T7352 condition and AFNOR7020 in T652 condition show some degree of anisotropy of mechanical properties with regard to yield strength and ultimate tensile strength. Higher degree of deformation leads to more pronounced anisotropy in mechanical properties with regard to yield strength and ultimate tensile strength, with a maxima along the transverse direction. For the alloys, experimentally measured Plastic Strain Ratio, r value, which is a measure of the texture present in the material in the deformation conditions, agree well with the computed values with a maximum at 45oorientation to the rolling direction.
Effect of Counter Surface Temperature and Load on the Transition from Mild to Severe Wear Behavior of Al-Si-SiCp Composites in Reciprocating Conditions
Authors: Rajeev V.R. , Dwivedi D.K. , Jain S.C.
Published: February 2012

In the present paper, the effect of counter surface temperature and load on the transition from mild to severe wear of A319/15%SiCp, A336/15%SiCp, and A390/15%SiCp composites have been reported. Composites were produced through stir casting route. Adhesive wear behavior of composites was studied under dry reciprocating conditions using indigenously developed reciprocating friction wear test rig conforming to ASTM standard G133-05. It was found that increase in counter surface temperature increases wear rate and depending upon the load and type of composite mode of wear changes from mild oxidative to severe metallic wear noticed. At 120N load, the critical transition temperature for all the three Al-Si-SiCp composites was found to be 350°C. SEM study of wear surface and wear debris was conducted to analyze the mode of wear and operating wear mechanism. Severe wear was characterized by massive plastic deformation and gross material removal while the mild wear was found to be associated with delamination and scoring as main wear mechanisms responsible for material loss.
Optimization of Homogenization Parameters of Al-Cu-Li Alloy Cast Ingots Using Calorimetry and Metallographic Techniques
Authors: Nayan Niraj , Murty S.V.S. Narayana , Sharma S.C. , Sreekumar K. , Sinha Parameshwar Prasad
Published: February 2012

In the present study, thermal treatments for homogenizing cast structures of Al-Cu-Li alloy AA2195 for improved workability are developed chiefly by empirical methods and detailed Differential Scanning Calorimetry (DSC) and microstructural characterization. DSC has been carried out on as-cast samples to establish the homogenization temperatures and avoid incipient melting. Homogenization time has been calculated empirically and microstructural characterization and DSC has been carriedout to after each cycle to validate the empirically established homogenization cycle. Homogenization cycle (435°C/8hrs+495°C/12hrs+525°C/32hrs) has been established for AA2195 alloy having an average grain size of 500μm based on calorimetric studies and microstructural examination.
Wetting Characteristics of Sn-0.7Cu Lead-Free Solder Alloy on Copper Substrates
Authors: Satyanarayan  , Prabhu K.N.
Published: February 2012

In the present work, the effect of surface texture on wetting characteristics of lead-free solder Sn-0.7Cu on copper substrates have been investigated at 298°C. The wetting tests were carried out using FTA 200 (First Ten Angstrom) dynamic contact angle analyzer. The surface texture of copper substrate significantly affected the wetting properties of Sn-0.7Cu solder alloy. Contact angles of about 30° were obtained on Cu substrate having smooth surface texture (Ra = 0.0155µm). On other hand contact angles on rough copper surface texture (Ra = 1.1194µm) were reduced to 20°. The contact angles decreased with increasing surface texture of Cu substrate. For rough Cu substrate, it seems that the solder atoms dissolve into the substrate in the time period of 200-600s.
Pulsed Thermography and Ultrasonic Non-Destructive Evaluation of Corrugated Metallic Thermal Protection System (MTPS) Panel
Authors: Hari Krishna S. , Kumar Ajay , Karthikeyan P. , Abilash M.P. , Narayanankutty N. , Kumar G. Sunil , Usha K.M. , Rakesh S.
Published: February 2012

Space vehicles that re-enter earth’s atmosphere require thermal protection system (TPS) to safeguard them from intense aerodynamic heating. Depending on the type of re-entry (lifting/ballistic), trajectory, duration of flight in atmospheric regime etc., the heat flux may vary from 40kW/m2to 180kW/m2. In our studies on metallic TPS (MTPS), corrugated core is joined to either side of the skins by brazing. The brazed joint is evaluated using both pulsed thermography (PT) and ultrasonic testing. PT images show clear visualization of joint and defects. Also it is faster and easier. Ultrasonic testing is done using pitch-catch and pulse-echo techniques, which shows many limitations. In literature, it is reported that for brazed joints using ultrasonic testing, defect location can be identified by faster decay pattern of multiple echoes (compared to that of good location). In case of PM 2000 panel, reversal of the patterns is observed. This new phenomenon is verified with the support of PT. It is also found that for inconel panel, the decay patterns are as reported in literature.
Friction Welding of Titanium to 304 Stainless Steel with Electroplated Nickel Interlayer
Authors: Cheepu Muralimohan , Muthupandi V. , Loganathan S.
Published: February 2012

Friction welding is a solid state joining process and it is best suited for joining dissimilar metals. It overcomes the problems associated with the conventional fusion welding processes. The joining of dissimilar metals using fusion welding processes produce brittle intermetallic precipitates at the interface which reduce the mechanical strength. Various aerospace, nuclear, chemical and cryogenic applications demand joints between titanium and stainless steel. Direct joining of these metals results in brittle intermetallics like FeTi and FexTiy, at the weld interface, which is to be avoided in order to achieve improved properties of the joints. Present study involves joining of two industrially important dissimilar metals such as commercially pure titanium and 304 stainless steel by friction welding with electroplated nickel coating as interlayer that can prevent the brittle intermetallic formation. Microstructural details of the interfaces of the friction welded joints were studied by optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) technique and X-ray diffraction (XRD). Microhardness survey was carried out across the joints and tensile test was conducted to assess the mechanical properties of the joints. Fractography studies were carried out on the fracture surfaces of the joints to know the region of failure as well as the mode of failure. XRD patterns indicate the presence of intermetallics in the friction welded joints. These two metals were successfully joined by having electroplated nickel as interlayer. The weld interface on titanium side contained Ti-Ni intermetallics layers, in which the hardness of the weld metal showing the higher value than the base metals. Fractography study conducted on the fracture surfaces created due to pull test reveals that the failure is by brittle fracture and occurred at the intermetallics layer. The maximum strength of the joints achieved for 30 μm and 50 μm thick electroplated nickel interlayers are 242 MPa and 308 MPa, respectively.
Effect of Deposition Time on the Characteristics of High Phosphorous Nickel Deposit, Deposited Using Electroless Route
Authors: Reddy Venkat Ram , Dixit Bharath , Udaya Bhat K.
Published: February 2012

Electroless Ni-high P alloy is deposited on commercial aluminium. Parameters are set so that deposit will be crystalline in nature with a very high phosphorous content. Deposition time is the variable. It is observed that all the deposits have nodular morphology indicating nucleation and growth phenomena. The nodules become coarse with increase in the deposition time. The deposit changes from clear crystalline to nanocrystalline with increase in deposition time. Coatings with lower deposition times have porosity in it.
Characterization of Fireside Corroded Sections of Boiler Tubes
Authors: Pavan A.H.V. , Vikrant K.S.N. , Nandi Somnath , Singh Kulvir
Published: February 2012

11/4Cr1/2Mo3/4Si (T11) and 21/4Cr1Mo (T22) grade steels are extensively used in critical parts of sub-critical thermal power plants like superheater, reheater tubes or headers. The tubes are designed to last for a very long time in service. These tubes are exposed to hot flue gas on the outer side and consequently, the inner side heats the steam passing through the tube. The outlet temperature of the steam ranges from 500-550°C. Therefore, not only the temperature on the outer side is much higher than the steam outlet but also the environment which the tube faces is extremely corrosive thereby leading to hot corrosion/ fireside corrosion. Some parts of the tubes are also exposed to fly ash coming from the combustion of coal leading to the formation of deposits on the tubes. In the present work, the tubes are cut and taken out during overhaul shutdowns and they are characterized by X-Ray Diffraction (XRD) for the likely phases that are formed on the surface of the fireside corroded layer. The deposits/scales are also qualitatively characterized. The cross-sections of the tubes are used for characterization of fireside corroded product layers using Optical Microscopy and Field Emission Scanning Electron Microscopy (FESEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDS). This work will be extended further to develop rate laws and rate mechanisms of the corrosion product layers formed on the service exposed tubes.
Comparison of Hydrogen Sensing Characteristics of CrNbO4 Prepared by Solid-State Route and Solution Combustion Synthesis (SCS)
Authors: Murthy A. Sree Rama , Gnanasekar K.I. , Jayaraman V. , Umarji A.M. , Gnanasekaran T.
Published: February 2012

Solution combustion synthesis is adopted for the preparation of CrNbO4. Its electrical conductivity is found to be less than that of the solid state synthesized compound. Hydrogen sensing property of solution-synthesized compound is comparable to that of solid-state prepared compound up to about 400 vppm of H2. However, the sensor signal saturates beyond 2500 vppm of H2. Hydrogen sensing property is compared between the combustion derived and solid state prepared compounds.
Thermally Grown Oxide Layer on Aluminized Superalloy 690 Substrate and its Stability in Nitrate-Based Environment
Authors: Dutta Rabi Sankar , Yusufali Chelakkattu , Majumdar Sanjib , Mishra Raman Kumar , Kaushik Chetan Parkash , Kshirsagar Rohidas Jagannath , Kulkarni Ulhas Digambar , Dey Gautam Kumar
Published: February 2012

Aluminides were formed on Ni-Cr-Fe based superalloy 690 substrates using pack aluminization process at 1273 K in controlled atmosphere. Thermal oxidation of aluminized specimens was carried out at 1273 K for a total period of 4 hours in air. The thermally grown oxide layer was examined using X-ray diffraction (XRD) studies on top surface and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) analysis along the cross-section of the sample. The oxide layer developed on aluminized superalloy 690 substrate consisted of Al2O3 layer with a thickness of about 2 μm. The oxidized specimens were exposed in nitrate-based environment (simulated high-level nuclear liquid waste) at 373 K for a total period of 216 hours. A good adherence of aluminide coatings was noticed even after prolonged exposure in nitrate-based solution with a little amount of material dissolution from the edges of the specimens. XRD studies on exposed specimen indicated existence of Al2O3 layer on the top surface, which is believed to have resulted in good adherence of aluminide coatings.
FTIR and DSC Study of Se92Te8-xSnx (x=0, 3 and 5) Chalcogenide Glasses
Authors: Kumar Rajneesh , Sharma Pankaj , Rangra Virsingh S.
Published: February 2012

In the present work, DSC and FTIR study of the of Se92Te8-xSnx ( x=0, 2 and 4) glassy samples has been studied. FTIR spectra was taken in wavelength region 50-600 cm-1. The parameters like theoretical wave number and activation energy of glass transition and crystallization has been calculated by Kissinger’method and Augis and Bennett’approximation. With the addition of Sn, Far-IR spectra shift toward high frequency side and new bands starts appearing in the spectra. The Sn atom appear to substitute for the selenium atoms in the outrigger sites due to large bond formation probability. Activation energy of glass transition increases with Sn addition while for crystallization, it also increases except at x=1.
Synthesis and Characterization of Hybrid ZnO@Ag Core-Shell Nanospheres for Gas Sensor Applications
Authors: Dinesh V. Ponnuvelu , Biji P. , Kumaravel M. , Tyagi A.K. , Kamaruddin M.
Published: February 2012

ZnO nanospheres were prepared by hydrothermal method using CTAB as protecting ligands. The purified ZnO nanospheres were functionalized using 3-aminopropyl-trimethoxysilane (APTMS) and made into core-shell nanostructures with in-situ reduction of Ag+ into silver nanoclusters. ZnO nanospheres act as the core while silver nanoclusters act as shell material resulting in the formation of ZnO@Ag core-shell nanostructures. The precursor ZnO nanospheres and ZnO@Ag core-shell nanostructures were well characterised structurally by UV-Visible, FT-IR, XRD, and TGA and morphologically by SEM and HR-TEM. The analysis confirms that Ag nanoclusters are attached to ZnO nanospheres with uniform distribution. The induced surface area of these hybrid core-shell structures with isolated nanoclusters on ZnO surface pointed towards the possibility of having better sensitivity as an excellent gas sensing material. The present investigation provided an easy synthetic platform for obtaining high surface area core-shell nanostructures which enhances interfacial compatibility between metal oxide core and metal shell by suitable functionalization for generating better gas sensing materials.
Global Patent Scenario of Materials: An IP Analysis
Authors: Nagashiresha G. , Sridhar T.S. , Chandra Sukla
Published: February 2012

There is an ever increasing demand and innovation worldwide in the area of materials research in aerospace industry. Research on materials is the focused area in aerospace sector because reducing aircraft/spacecraft weight and/or increasing the temperature capabilities is the key factor in increasing the performance. Hence there is always an urge on the development of advanced materials especially in the area of light weight, High temperature resistant materials. There are different ways of keeping abreast on current state of art on the development of advanced materials namely reading Journal publications, attending conferences/seminars or performing intellectual property (IP) analysis specifically looking at patents. Patent portfolio indicates the technology and research direction of a company. Intellectual property plays a key role in the present global competitive world. It is not only an asset for the company but also helps in increasing the bottom line of an organization. Hence, an attempt was made to look at the global patent scenario of materials used for aerospace industry. A high level scan of aerospace materials patent portfolio in the past 20 years was done to understand the current technology focus and trend of materials research. The study was restricted to Aerospace/Aviation Players. Four different types of Materials are considered for the study namely Light weight metals (includes Al and Ti alloys), Superalloys, High temperature coatings and Composites. A further deep dive analysis on the above materials has been done to understand the Industry focus on various technology areas such as Manufacturing, Inspection, Application etc. This analysis helps technologists in understanding the current state of art and research focus in Materials area specific to Aerospace/Aviation Industry
Design of Digital Electronics for High Temperature Using Basic Logic Gates Made of 4H-SiC MESFETs
Authors: Alexandru Mihaela , Banu Viorel , Vellvehi Miguel , Godignon Philippe , Millán José
Published: February 2012

– 4H-SiC MESFET transistors are very attractive devices for high temperature application and communications. The JFET and MESFET transistors have a promising potential for integrated circuits able to operate at high temperature and harsh radiation environments, due to the superior electrical, mechanical and chemical proprieties of 4H-SiC. Progresses in the manufacturing of high quality SiC substrates open the possibility to new circuit applications.
Visible and Deep Ultraviolet Study of SiC/SiO2 Interface
Authors: Borowicz Pawel , Gutt Tomasz , Malachowski Tomasz , Latek Mariusz
Published: February 2012

Silicon carbide (SiC) is a wide band gap semiconductor having good thermal conductivity and high break down voltage. Formation of SiO2 layer in thermal oxidation process completes the set of properties of SiC as a promising material for fabrication of high power and high frequency electronic devices. This picture is perturbed by Near Interface Traps (NIT's) that decrease the surface mobility of charge carriers. The origin of NIT's is still the subject of discussion and there are several candidates for NIT's. One possibility is the formation of carbonic structures during the process of manufacturing of MOS-type structures. The aim of this work was to look for possible carbonic inclusions with Raman spectroscopy. The attention of authors was focused on non-destructive way of application of the experimental technique.
Structural Characterization of Graphene Grown by Thermal Decomposition of Off-Axis 4H-SiC (0001)
Authors: Giannazzo Filippo , Rambach Martin , Lerch Wielfried , Bongiorno Corrado , Di Franco Salvatore , Rimini Emanuele , Raineri Vito
Published: February 2012

We present a nanoscale morphological and structural characterization of few layers of graphene grown by thermal decomposition of off-axis 4H-SiC (0001). A comparison between transmission electron microscopy (TEM) in cross-section and in plan view allows to fully exploit the potentialities of TEM. Such a comparison was used to get information on the number of graphene layers as well as on the rotational order between the layers and with respect to the substrate. Some peculiar structures observed by TEM (wrinkles) could only be systematically measured by atomic force microscopy (AFM). In particular, the density and the height of the wrinkles in the few layers of graphene was investigated.
Seeding Layer Influence on the Low Temperature Photoluminescence Intensity of 3C-SiC Grown on 6H-SiC by Sublimation Epitaxy
Authors: Zoulis Georgios , Sun J.W. , Vasiliauskas Remigijus , Lorenzzi Jean , Peyre Hervé , Syväjärvi Mikael , Ferro Gabriel , Juillaguet Sandrine , Yakimova R. , Camassel Jean
Published: February 2012

We report on n-type 3C-SiC samples grown by sublimation epitaxy. We focus on the low temperature photoluminescence intensity and show that the presence of a first conversion layer, grown at low temperature, is not only beneficial to improve the homogeneity of the polytype conversion but, also, to the LTPL signal intensity. From the use of a simple model, we show that this comes from a reduced density of non-radiative recombination centers.
On Applicability of Time-Resolved Optical Techniques for Characterization of Differently Grown 3C-SiC Crystals and Heterostructures
Authors: Ščajev Patrik , Onufrijevs Pavels , Manolis Georgios , Karaliūnas Mindaugas , Nargelas Saulius , Jegenyes Nikoletta , Lorenzzi Jean , Ferro Gabriel , Beshkova Milena , Vasiliauskas Remigijus , Syväjärvi Mikael , Yakimova Rositza , Kato Masashi , Jarašiūnas Kęstutis
Published: February 2012

We applied a number of time-resolved optical techniques for investigation of optical and photoelectrical properties of cubic SiC grown by different technologies on different substrates. The excess carriers were injected by a short laser pulse and their dynamics was monitored by free-carrier absorption, light-induced transient grating, and photoluminescence techniques in a wide excitation range. Combining an optical and electrical probe beam delay, we found that free carrier lifetimes in differently grown layers vary from few ns up to 20 μs. Temperature dependences of carrier diffusivity and lifetime revealed a pronounced carrier trapping in thin sublimation grown layers. In free-standing layers and thick sublimation layers, the ambipolar mobility was found the highest (120 cm2/Vs at room temperature). A linear correlation between the room-temperature band edge emission and carrier lifetime in differently grown layers was attributed to defect density, strongly dependent on the used growth conditions.
Low Temperature Photoluminescence Investigation of 3-Inch SiC Wafers for Power Device Applications
Authors: Peyre Hervé , Sun J.W. , Guelfucci Jude , Juillaguet Sandrine , ul Hassan Jawad , Henry Anne , Contreras Sylvie , Brosselard Pierre , Camassel Jean
Published: February 2012

Focusing on the change in aluminium-related photoluminescence lines in 4H-SiC versus doping concentration, we have used a combination of LTPL (Low Temperature PhotoLuminescence) and secondary ion mass spectrometry measurements to set new calibration curves. In this way, one can probe the change in aluminum concentration in the range 1017 to 1019 cm-3. When applied to LTPL maps collected on full 3-inch wafers, we show that such abacuses constitute a powerful tool to control efficiently the doping level of as-grown p+ (emitters) and p++ (contact) layers for power device applications.
Evaluation of Correct Value of Richardson's Constant by Analyzing the Electrical Behavior of Three Different Diodes at Different Temperatures
Authors: Zaman Muhammad Yousuf , Perrone Denis , Ferrero Sergio , Scaltrito Luciano , Naretto Marco
Published: February 2012

Various attempts have been made to evaluate the correct value (A*=146 A/cm2.K2) ofRichardson's constant. In 2005 S. Ferrero et al. published their research in which they performedan analysis of electrical characterizations of twenty Ti/4H-SiC(titanium on silicon carbide) Schottkydiodes with the help of thermionic emission theory and evaluated the value of Richardson's constantto be 17±8 A/cm2.K2; which is very low as compared to the theoretical value of 146 A/cm2.K2.Wehave tried in this paper to evaluate the Richardson's constant's value by nearly same experimental tech-niques followed by S. Ferrero et al. and additionally, have applied Tung's theoretical approach whichdeals with the incorrect value of A* in the perspective of Schottky barrier inhomogeneities caused bythe presence of nanometer size low barrier patches present in the uniform high barrier of the Schottkydiode.We have fabricated two Ti/4H-SiC (titanium on silicon carbide) Schottky diodes with differentareas and oneMo/4H-SiC (molybdenumon silicon carbide) Schottky diode. In this paper we have pre-sented a comparative analysis of forward current-voltage characteristics of all three Schottky diodes.In all three cases we were successful in the evaluation of nearly correct value of Richardson's constant.This work emphasizes the effects of differentmetal-SiC combinations and laboratory environments onthe evaluation of Richardson's constant and the effective area involved in the current transport. As pre-dicted by Tung's model the effective area is seen to be substantially different from the geometric areaof the Schottky diode. Evaluated values of A*, with an error of ±2, come out to be 145.39, 148.33and 148.33 A/cm2.K2for Ti/4H-SiC(large area), Mo/4H-SiC and Ti/4H-SiC(small area) Schottkydiodes, respectively.
Ti Thickness Influence for Ti/Ni Ohmic Contacts on N-Type 3C-SiC
Authors: Biscarrat Jérôme , Song Xi , Michaud Jean François , Cayrel Frédéric , Portail Marc , Zielinski Marcin , Chassagne Thierry , Collard Emmanuel , Alquier Daniel
Published: February 2012

We report on the influence of titanium thickness on the structural and electrical properties of annealed Ti/Ni ohmic contacts on highly doped n-type 3C-SiC. Electrical analysis by means of circular transfer length method demonstrate that an interlayer of titanium with thickness in the range of 25-150 nm has no significant influence on specific contact resistance. However, from a structural point of view, the formation of nickel silicides as well as Ti3SiC2 is severely affected by the titanium thickness. Moreover, the Kirkendall effect due to the reaction between Ni and SiC is influenced by the titanium thickness. In fact, Scanning Electron Microscopy analysis demonstrates that the adjunction of titanium affects the distribution of Kirkendall voids in the contact. Current maps determined by conductive Atomic Force Microscopy reveal significant variation of uniformity according to the titanium thickness.
Investigation of Al-Ti Ohmic Contact to N-Type 4H-SiC
Authors: Drevin-Bazin Alexia , Barbot Jean Francois , Cabioch Thierry , Beaufort Marie France
Published: February 2012

Metal/semiconductor contacts have a great impact on device performances. Contact properties to wide band gap semiconductors, in particular, are more difficult to control due to the large potential barrier which arises when the metal is deposited on the semiconductor’s surface. Moreover, intrinsic interface states also lead to deviation of the Schottky-Mott limit and the barrier height is no more dependent of the work function of the metal. The contact property has also become very important with the race for miniaturisation toward the nanoscale. Contacts must also be adherent, able to resist to the temperatures for which SiC based-devices are intended, and also they should be compatible with conventional device processing techniques (die attachment). Ohmic contacts to SiC have thus been investigated for decades. The difficulties of controlling the interface properties between the metal and SiC to obtain low resistive ohmic contact have not been overcome yet; the specific contact resistance being proportional to the exponential of the barrier height for a given doping concentration. For example, nickel has been studied for the ohmic contacts on n and p-type, however the presence of voids at the interface has been reported leading to the degradation of the contact properties [1]. More recently low ohmic contact resistance has been reported of Au/Ti/Al/n-type-4H-SiC contact [2]. The formation of TiSi, TiSi2 and Ti3SiC2 has been reported according to x-ray diffraction experiments after annealing. The formation of Ti3SiC2 (or MAX phase) has also been reported in TiAl-based contacts to both n-and p-type [3-6]. This ternary carbide layer is supposed to reduce the barrier height at the contact and thus leads to low contact resistances. The addition of Ge also leads to the formation of Ti3SiC2 at lower temperature of annealing [7]. However, other compounds are frequently observed at the interface showing that the control of the interfacial structure must be optimized. The objective of our work is to obtain uniform epitaxial Ti3SiC2 thin film on n-type 4H-SiC to form ohmic contact with low resistance by studying the influence of different parameters such as the role of Aluminium on the formation mechanisms, the polarity and doping dependence. The temperature and the annealing time are also parameters to be optimized for the improvement of the ohmic contact.
MOCVD Grown AlGaN/GaN Transistors on Si Substrate for High Power Device Applications
Authors: Selvaraj S. Lawrence , Egawa Takashi
Published: February 2012

An extensive study on the use of Si as a substrate for the growth of AlGaN/GaN layers for High-Electron-Mobility Transistor (HEMT) were studied and reported in this article. We have used thick buffers to grow high resistive i-GaN by MOCVD which offers a high breakdown voltage. While the leakage through buffer and substrate can be controlled by thick buffer, the leakage through gate is controlled using a thin 2-nm in-situ grown i-GaN cap layer. We have evidenced a high figure of merit (BV2/RON) of 2.6 x 108 V2Ω-1cm-2 for AlGaN/GaN HEMTs grown on 4-inch Si substrate. The challenges before the MOCVD growth of GaN on Si is also discussed in detail.
Investigations on the Origin of the Ohmic Behavior for Ti/Al Based Contacts on n-Type GaN
Authors: Thierry-Jebali Nicolas , Ménard Olivier , Dubois Christiane , Tournier Dominique , Collard Emmanuel , Brylinski Christian , Cayrel Frédéric , Alquier Daniel
Published: February 2012

This work reports of investigation on the origin of the ohmic behavior for Ti/Al basedcontacts on n-GaN. Indeed, last publications tend to prove that the ''nitrogen vacancy'' theory is notconfirmed by the experimental ground available. To find new answers, we first made electrical charac-terizations on some Al/Ti/n+-GaN contacts with different annealing conditions. Then, we performedSIMS depth profiles of annealed TiN/Ti/n+-GaN samples. Results developed in this paper tend todemonstrate that the ohmic behavior of Ti/Al based contact is mainly due to an increase of the dop-ing concentration. Moreover, the high doping level can be explained by an in-diffusion of Ti and anexo-diffusion of Si elements close to the metal / semiconductor interface.
The Influence of C3H8 and CBr4 on Structural and Morphological Properties of 3C-SiC Layers
Authors: Attolini Giovanni , Bosi Matteo , Watts Bernard Enrico , Battistig Gábor , Dobos László , Pécz Béla
Published: February 2012

In this work we report on the growth of cubic silicon carbide using CBr4 and silane as precursors at different C3H8/CBr4 flow ratios. The layers were deposited on 2’’ (001) Si wafers by means of the VPE technique in a horizontal cold-wall reactor with induction heating. The growths were performed at atmospheric pressure, in H2 atmosphere and involved several steps: Si thermal etching; carburisation; epitaxial growth. Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were performed to observe the film morphology and defects and correlate them with the gas phase composition. Results show that the addition of CBr4 to the standard SiH4 and C3H8 precursor can change the crystalline nature and the morphology of the grown SiC.
Transmission-Electron-Microscopy Observations on the Growth of Epitaxial Graphene on 3C-SiC(110) and 3C-SiC(100) Virtual Substrates
Authors: Handa Hiroyuki , Ito Shun , Fukidome Hirokazu , Suemitsu Maki
Published: February 2012

By conducting a heteroepitaxy of a 3C-SiC film on a Si substrate and by annealing its surface in a UHV ambient, epitaxial graphene can be formed on such 3C-SiC virtual substrates. While the growth on the Si-terminated 3C-SiC(111)/Si (111) surface is known to proceed in a similar manner as on the Si-terminated 6H-SiC(0001) surface, successful growth of graphene on 3C-SiC(100)/Si (100) and 3C-SiC(110)/Si (110) surfaces remains puzzling. We have carried out detailed cross-sectional transmission-electron-microscopy observations on these systems to find out that (111)-facets may play crucial roles in the initiation of graphene on these surfaces. This observation also accounts for the absence of the interface layer at the graphene/SiC in these orientations.
Progress in 3C-SiC Growth and Novel Applications
Authors: Yakimova Rositza , Vasiliauskas Remigijus , Eriksson Jens , Syväjärvi Mikael
Published: February 2012

Recent research efforts in growth of 3C-SiC are reviewed. Sublimation growth is addressed with an emphasis on the enhanced understanding of polytype stability in relation to growth conditions, such as supersaturation and Si/C ratio. It is shown that at low temperature/supersaturation spiral 6H-SiC growth is favored, which prepares the surface for 3C-SiC nucleation. Provided the supersaturation is high enough, 3C-SiC nucleates as two-dimensional islands on terraces of the homoepitaxial 6H-SiC. Effect of different substrate surface preparations is considered. Typical extended defects and their electrical activity is discussed. Finally, possible novel applications are outlined.
Consideration on the Thermal Expansion of 3C-SiC Epitaxial Layer on Si Substrates
Authors: Severino Andrea , Camarda Massimo , La Magna Antonino , La Via Francesco
Published: February 2012

3C-SiC lattice parameters, both in-plane and out-of-plane, have been studied as a function of the temperature (up to 773 K) by performing X-Ray Diffraction (XRD) measurements in coplanar and non-coplanar geometry during the thermal treatments. A tetragonal distortion of the 3C-SiC cell has been observed, with a=b≠c, resulting from a tensile stress status induced by the presence of Si substrate. A linear expansion coefficient of about 4.404 × 10-6 K-1 at 773 K has been obtained for a 15 μm thick 3C-SiC film grown on (100) Si substrate. The discrepancy with the value reported in literature of 5.05 × 10-6 K-1 at 800 K [Slack et al., Journal of Applied Physics 46, 89 (1975)] may be related to the different nature of samples used.
Epitaxial Growth of 3C-SiC onto Silicon Substrate by VLS Transport Using CVD-Grown 3C-SiC Seeding Layer
Authors: Berckmans Stéphane , Auvray Laurent , Ferro Gabriel , Cauwet François , Soulière Véronique , Collard Emmanuel , Quoirin Jean Baptiste , Brylinski Christian
Published: February 2012

The crystal growth of 3C-SiC onto silicon substrate by Vapour-Liquid-Solid (VLS) transport has been investigated. In the studied growth configuration, propane feeds a SiGe liquid phase contained in 10 µm-deep etched trenches on the Si substrate. Before SiGe deposition, the substrate surface and the trench walls were coated with a thin (100 - 200 nm) CVD-grown 3C-SiC seeding layer. For the VLS growth, the temperature was increased up to 1280°C, above the SiGe alloy melting point, at which point propane was added to start VLS growth. X-ray diffraction shows that some SiC is grown epitaxially onto the CVD seeding layer. However, cross-section SEM observations have evidenced that SiC has grown as trapezoidal islands and not as an uniform layer. Backscattered electron images also clearly show a deep penetration of germanium into the substrate through the SiC seeding layer. This penetration was found to be strongly reduced when increasing the seeding layer thickness from 100 to 200 nm.
Study of 3C-SiC Mechanical Resonators, Filters and Mixers
Authors: Mastropaolo Enrico , Cheung Rebecca
Published: February 2012

The design, fabrication and characterisation of flexural-mode 3C-SiC resonators are presented. Single-clamped, double-clamped beams and circular membranes, with aluminium and platinum electrodes patterned on top, have been implemented. The structures’ resonant frequency has been investigated optically when the devices are actuated mechanically and electro-thermally. Electro-thermal mixing of two input electrical signals with two different frequencies has been demonstrated. The temperature stability of the 3C-SiC resonators has been characterised.