bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Delamination Fracture for Enhanced Impact Toughness in 0.05 %P Doped High Strength Steel with Ultrafine Elongated Grain Structure
Authors: Jafari Meysam , Kimura Yuuji , Tsuzaki Kaneaki
Published: December 2011

Ultrafine elongated grain (UFEG) structures with strong <110>// rolling direction (RD) fiber deformation texture were produced by warm caliber-rolling at 773 K, namely tempforming in the 1200 MPa-class medium-carbon low-alloy steel with phosphorous (P) contents of 0.001 and 0.053 mass%. Charpy impact tests were performed at temperature range of-196 to 150 °C on the UFEG structure. Regardless of P content, high upper shelf energy about 145 J and a very low ductile to brittle transition temperature (DBTT) of around-175 °C were obtained. P segregation embrittlement completely disappeared in the 0.053 %P steel and both steels showed ductile fracture on the planes normal to RD at temperature range of-150 to 150 °C. The main reason for the high upper shelf energy and very low DBTT in the 0.053 %P steel would be delamination fracture along RD when both 0.001 and 0.053 %P steels showed quite similar microstructures including texture. Since the occurrence of delamination requires relatively weak interfaces or planes, P segregated to the ferrite grain boundaries and interfaces of cementite particles-ferrite matrix and made them feasible paths for crack branching and consequently delamination occurred. We showed in this work the advantage of delamination (crack arrester-type) on the high absorbed energy obtained by 0.053 %P steel in comparison with 0.001 %P steel.
Dissimilar Friction Stir Welding of 2014 to 6061 Aluminum Alloys
Authors: Jonckheere Caroline , de Meester Bruno , Denquin Anne , Simar Aude
Published: December 2011

Welding cheap and ductile 6xxx Al alloys with high strength 2xxx Al alloys is desirable for instance in specific aeronautical applications. These alloys present different rheological behaviors and melting temperatures which affect the ability to produce sound dissimilar friction stir welds. Dissimilar friction stir butt welds made of 2014-T6 and 6061-T6 Al alloys were performed with various welding parameters including shifts of the tool from the initial separation between the plates to be welded and placing one alloy either on the advancing, or on the retreating side of the weld. Temperature measurements during welding, mechanical characterization (transverse tensile tests and hardness profiles) and macrographic observations were performed. Macrographies on sections perpendicular to the welding direction reveal different metal flow patterns in the weld nugget. If the 2014 alloy is placed on the advancing side of the weld, an abrupt transition between the weld nugget and the 6061 alloy is observed on macrographs leading to premature fracture in tension. Dissimilar welds are cooler on the 6061 side of the weld, i.e. the weakest side of the weld, than the corresponding 6061 similar weld, limiting the growth of the hardening precipitates. This leads thus to higher strength of the dissimilar welds. Dissimilar welds with the weld center shifted towards the 2014 alloy present lower temperatures than unshifted welds on the 6061 side of the weld, also leading to higher strength.
Microstructure Characterization of Friction Stir Spot Welded TRIP Steel
Authors: Lomholt Trine C. , Adachi Yoshitaka , Peterson Jeremy , Steel Russell , Pantleon Karen , Somers Marcel A.J.
Published: December 2011

Transformation Induced Plasticity (TRIP) steels have not yet been successfully joined by any welding technique. It is desirable to search for a suitable welding technique that opens up for full usability of TRIP steels. In this study, the potential of joining TRIP steel with Friction Stir Spot Welding (FSSW) is investigated. The aim of the study is to investigate whether acceptable welds can be produced, and additionally, to obtain an understanding of the microstructural changes during welding. The microstructure was investigated with a combination of microscopical techniques with the aim of identifying the transformations occurring during welding. Reflected light microscopy, scanning electron microscopy, and electron backscatter diffraction were among the methods applied for detailed investigations. The microstructure adjacent to the welds can generally be subdivided in two thermo-mechanically affected zones (TMAZ), and two heat-affected zones (HAZ). The dual behavior of the microstructure in the zones is related to the two transition temperatures in steel: A1 and A3. In parts of the TMAZ the microstructure contains ultra fine-grained ferrite. This finding parallels the observation in thermo-mechanically processed steels, where severe deformation at elevated temperatures is used to produce ultra fine-grained microstructures. Several possible transformation mechanisms could in principle explain the development of ultra fine-grained ferrite, e.g. dynamic recrystallization, strain-induced ferrite transformation and dynamic recovery.
Discontinuous and Continuous Precipitation during Aging in Mg-Al System Alloys
Authors: Ebata Yuhei , Furui Mitsuaki , Ikeno Susumu , Sakakibara Katsuya , Saikawa Seiji
Published: December 2011

In this study, age-hardening behavior of Mg-Xmass%Al alloys (X=3, 4.5, 6, 7.5 and 9mass%) were investigated by Vickers hardness measurement and optical microscopic observation. Each alloy was solution-treated and then isothermal-aged at 473, 498 and 523K. In the case of aluminum content less than 6mass%, Mg-3mass%Al and Mg-4.5mass%Al alloys, occurred insignificant age hardening. In the case of aluminum content higher than 6mass%, Mg-6mass%Al, Mg-7.5mass%Al and Mg-9mass%Al alloys, occurred remarkable age hardening. For each aging temperature, with heighten aluminum content, increase the value of maximum hardness and shorten time to maximum hardness. Mean hardness of discontinuous precipitation during aging increased with lower aging temperature and higher aluminum content. Furthermore, over-aged microstructure of Mg-Al system alloys differed from aluminum content or aging temperature.
Effect of Zn Content on Aging Behavior of Binary Mg-Zn Alloys
Authors: Nakanishi Ryosuke , Kawabata Tokimasa , Matsuda Kenji , Ikeno Susumu
Published: December 2011

The Vickers micro hardness measurements and high resolution transmission electron microscopy (HRTEM) observation were carried out to investigate the effect of Zn content on aging behavior of Mg-Zn alloys. The hardness increased drastically after aging at 473 K in the Mg-Zn alloys with higher Zn concentration. And higher maximum hardness was obtained at the earlier aging time in the alloys with higher Zn concentration. In bright field image and HRTEM, the particle shaped contrasts of the precipitates were not appeared in 3.8%Zn. The particle shaped contrasts of the precipitates were appeared as indicated by arrows in 4.7 and 6.5%Zn. The contrasts of row on {110}Mg planes and the β1’ phase appeared in the water quenched 4.7 and 6.5%Zn alloy age at 473 K for 3.6 ks.
Effect of Grain Size on Microstructure and Aging Behavior in AM60 Magnesium Alloy
Authors: Takano H. , Furui Mitsuaki , Ikeno Susumu , Yamaguchi Tomoyasu , Saikawa Seiji
Published: December 2011

Our recent studies showed that continuous and cellular precipitates are covered with the whole of crystal grain in age hardable AM60 magnesium alloy cast into permanent molds, which have the average grain size of 75-85μm. Also, continuous precipitation is generated nearby grain boundary in the same alloys cast into sand molds, which have the average grain size of 138-147μm. It’s thought that permanent mold castings have the age hardening behavior of intragranular precipitation participation type that is influenced by continuous precipitates. It’s also thought that sand mold castings have the age hardening behavior of grain boundary participation type that is influenced by cellular precipitates. In this study, AM60 magnesium alloy with larger grain size was used to detect the grain size dependence of microstructure and aging behavior. In the microstructure of as-cast condition, the larger the grain size, it was shown that the none-equilibrium crystallized β phase with eutectic reaction during the solidification between liquidus and solidus temperatures becomes large-size. In the age hardening curves, the peak hardness values become higher with decreasing of grain size.
Crystallographic Orientation Relationship between Discontinuous Precipitates and the Matrix in AM-Series Alloys
Authors: Watanabe Katsumi , Matsuda Kenji , Kawabata Tokimasa , Ikeno Susumu
Published: December 2011

Magnesium alloys have received considerable attention because of their lightweight and recyclability. AM-series and AZ-series Mg-Al alloys have been used for industrial products widely, particularly for AM-series alloys because of better toughness and impact absorption properties than AZ-series alloys. The Mg17Al12intermetallic compound is the only precipitate formed during ageing after the solution heart treatment. Discontinuous precipitates exist in grain boundary randomly, and continuous precipitates exist in the matrix. However, there is few report about the orientation relationship between the discontinuous precipitates and the matrix. The purpose of this study is to investigate the orientation relationship between the discontinuous precipitates and the matrix of AM-series magnesium alloys. Hardness measurement, SEM observation, the electron backscattered diffraction (EBSD) techniques were preformed in order to understand the relationship between the discontinuous precipitate and crystallographic orientation of grains in AM-series magnesium alloy. TEM samples with discontinuous precipitates were prepared using the focused ion beam (FIB). And TEM observation was performed to investigate the discontinuous precipitates and crystallographic orientation in the matrix.
Morphological and Crystallographic Characterizations of the Ca-Mg-Zn Intermetallics Appearing in Ternary Diffusion Couples
Authors: Zhang Yi Nan , Kevorkov Dmytro , Bridier Florent , Medraj Mamoun
Published: December 2011

In the present research, seven multi-phase diffusion couples, with terminal alloys having different microstructural features, were prepared and annealed for 4 weeks at 335°C. The phase relations and change of morphological characteristics of each phase were studied along the diffusion zone by means of scanning electron microscopy/energy dispersive X-ray spectroscopy and quantitative electron probe microanalysis. Depending on the different terminal compositions of the diffusion couples, the morphological evolution in the diffusion zone can be: tooth-like, matrix phase with isolated and/or dendritic precipitates. Electron back-scattered diffraction analysis was carried out to investigate the crystal orientation of the ternary compounds and the crystal orientation relations at the interface of the diffusion zones.
The Influence of Alloying Elements on Grain Boundary and Bulk Cohesion in Aluminum Alloys: Ab Initio Study
Authors: Razumovskiy Vsevolod I. , Razumovskii Igor M. , Ruban Andrei V. , Butrim V.N. , Vekilov Yu.Kh.
Published: December 2011

The effect of B, Si, P, Cr, Ni, Zr and Mg on cohesive properties of Al and the special grain boundary (GB) Σ5 (210)[100], as well as their segregation behavior at the GB and the (210) surface are studied by first principles method. The analysis of these parameters allows us to single out Ni as the best and phosphorus as the worst interatomic bond strengthening alloying elements.
Highly Sensitive Pure and Pd-Doped LaFeO3 Nanocrystalline Perovskite-Based Sensor Prepared by High Energy Ball Milling
Authors: Ghasdi Mohammad , Alamdari Houshang
Published: December 2011

Pure nanostructured LaFeO3 with crystallite size of around 13 nm and specific surface area of 48 m2/g were prepared using high energy ball milling. 0.4, 2 and 5 wt% of Pd was impregnated on synthesized LaFeO3. TPD-O2, TPD-CO and TPR-H2 were performed to find the effect of Pd loading on perovskite oxide properties.CO gas sensing properties of doped and pure formulation were investigated. These results showed that 2 wt% Pd had optimum response ratio which had a maximum response ratio of 1200% with respect to 100 ppm CO in air at 140°C.
Crystallographic Features of the A-Type and CE-Type Antiferromagnetic States in the Simple-Perovskite Manganite System Sr1-xNdxMnO3
Authors: Onezawa Yusuke , Inoue Yasuhide , Arao Masazumi , Koyama Yasumasa
Published: December 2011

The electronic states of Sr1-xNdxMnO3 with the simple perovskite structure are characterized by a three-dimensional highly-correlated electronic system. To understand the detailed features of the A-and CE-type antiferromagnetic states in this system, their crystallographic features for x = 0.47, 0.48, and 0.50 have been investigated mainly by both x-ray powder diffraction and transmission electron microscopy. It was found at room temperature that the crystal structure for x = 0.47 was determined to have the monoclinic C2/m symmetry, while the orthorhombic Imma structure was confirmed for x = 0.48 and 0.50. The in-situ observation for x = 0.47 indicated that, in the heating process from room temperature, the C2/m-to-Imma transition occurred in the paramagnetic state, and that the A-type antiferromagnetic state appeared below about 200 K on cooling. In addition, the cooling from room temperature for x = 0.48 and 0.50 resulted in the direct transitions from the orthorhombic Imma state to the A-and CE-type antiferromagnetic states, respectively. Based on these features, we simply discussed the physical origin of the appearance of the paramagnetic state with the monoclinic symmetry for x = 0.47.
Fabrication of Organic-Inorganic Nano-Hybrid Materials Containing Oligothiophene Derivatives
Authors: Sato Mikio , Yoshizawa-Fujita Masahiro , Takeoka Yuko , Rikukawa Masahiro
Published: December 2011

Oligothiophene derivatives, 4,4’-bis-(2-aminoethylthienyl)-3,4-ethylenedioxythiophene dihydrohalide (AET-EDOT·HX: X = I, Br), were synthesized by Grignard coupling reactions. The hybrid films of oligothiophene and lead halide were fabricated by casting and spin-coating methods. The effect of halogen species on the optical properties of the perovskites was investigated. The X-ray diffraction profiles of (AET-EDOT)PbX4 cast films indicated that the layered structures were formed by the self-organization. After hybridization of AET-EDOT·HX with PbX2, new absorption peaks due to the confined excitons were observed at 400 nm for (AET-EDOT)PbBr4 film, and at 395 nm for (AET-EDOT)PbI4 film. These results indicated that the diamino-type oligothiophenes were successfully incorporated into the organic-inorganic layered perovskites. AFM images of (AET-EDOT)PbX4 cast films showed polycrystalline grains, indicating that the polycrystalline structures covered on the substrate surface.
Presence of the Ferroelectric Monoclinic State in the Mixed Ferroelectric System Ba(Ti1-xZrx)O3
Authors: Tsukasaki Hirofumi , Koyama Yasumasa
Published: December 2011

The mixed-oxide system Ba (Ti1-xZrx)O3 (BTZ) with the simple perovskite structure was reported to exhibit the remarkable dielectric response around x = 0.08. In order to understand the origin of the response, we have investigated the crystallographic features of ferroelectric states in BTZ with 0 ≤ x ≤ 0.15 mainly by transmission electron microscopy. According to the constructed phase diagram of BTZ, when the Zr content increases from x = 0 around 300 K, the ferroelectric tetragonal state in BaTiO3 is changed into the ferroelectric orthorhombic state around x = 0.03, and then into the ferroelectric monoclinic state around x = 0.06. That is, the monoclinic state with a polarization vector in the {110}PC planes is present in BTZ with 0.07 ≤ x ≤ 0.15, where the subscript PC denotes the paraelectric cubic state. The notable feature of the monoclinic state is that it exhibits the herringbone-type domain structure consisting of nanometer-sized ferroelectric domains. It is thus understood that the remarkable dielectric response in BTZ should be associated with the presence of nanometer-sized domains with the monoclinic symmetry.
Thermal Conductivity and Electrical Resistivity in Polycrystalline and Nanocrystalline Nickel
Authors: Wang S. , Brooks I. , McCrea J.L. , Palumbo G. , Cingara G. , Erb Uwe
Published: December 2011

The grain-size dependences of thermal conductivity and electrical resistivity of polycrystalline and nanocrystalline nickel were measured by the flash method and four-point probe method, respectively. Nanocrystalline nickel (grain size: 28 nm) was made by the pulsed-current electrodeposition process, while polycrystalline nickel (grain size: 57 μm) was the same material in fully annealed condition. Noticeable differences in thermal conductivity and electrical resistivity were observed for both materials. These results can be explained on the basis of the rapid increase in the intercrystalline grain boundary and triple junction volume fractions at very small grain sizes. The relationship between thermal conductivity and electrical resistivity of nanocrystalline nickel follows the classic Wiedemann-Franz law.
Debonding Characterization of SMA/Polymer Morphing Structures
Authors: Fischer Charles , Terriault Patrick , Brailovski Vladimir
Published: December 2011

morphing structures are expected to play an increasingly important role in aeronautic applications, among others. Shape memory alloys (SMA) are one of the most promising candidates to date. However, work remains to be done before these structures meet the stringent requirements of their successful integration in an aeronautic context. Research has shown that SMA/Polymer interface strength can be a limiting factor in active deformable structure performance. In this study, the effect on the SMA/Polymer interface strength of various surface treatments, wire geometries and resin types are evaluated. SMA wire geometry is modified through a specific combination of cold rolling and post-deformation annealing, which is capable of maintaining SMA actuating properties while achieving required cross-section area reductions. The most promising thermomechanical processing is finally proposed but results show that further work is required before SMA active elements can safely be used in an active structure.
Aging Behavior of Al-Mg-Ge Alloys with Different Mg2Ge Contents
Authors: Murakami Tomoatsu , Matsuda Kenji , Nagai Takeshi , Nakamura Junya , Kawabata Tokimasa , Ikeno Susumu
Published: December 2011

It is known that Al-Mg-Ge alloy shows the similar precipitation sequence to Al-Mg-Si alloy, and its equilibrium phase is β-Mg2Ge according to its phase diagram. In this study, the precipitation sequence of Al-Mg-Ge alloys containing different contents of Mg2Ge has been investigated by hardness test, TEM and HRTEM observation to understand the effect of Mg2Ge contents on age-hardening behavior of the alloys. The hardness of as-quenched and peak-aged samples have been improved by increasing Mg2Ge contents. The precipitates in the peak-aged samples have been classified into some metastable phases, such as the β’-phase and parallelogram-type precipitate by HRTEM observation. The relative frequency of these precipitates in the is has been changed with Mg2Ge contents.
Very Hard Synchrotron X-Ray Radiation as an Advanced Characterization Method Applied to Advanced High-Strength Steels
Authors: Carmele Dagmar , Rieger Thomas , Herrmann Klaus , Meyer Stephan , Lippmann Thomas , Stark Andreas , Bleck Wolfgang , Klemradt Uwe
Published: December 2011

Innovative steel materials of the third generation of advanced high-strength steel (AHSS) are based on complex multiphase microstructures on a submicron scale, which are adjusted in a heat treatment procedure. Established methods for microstructural characterization are usually applied after the heat treatment process (ex-situ) at room temperature and comprise amongst others X-ray analysis based on laboratory tubes with photon energies of several keV. The corresponding penetration depths are on the micron scale. Additionally, the results may be affected by the metallographic preparation process. Using very hard synchrotron X-ray radiation with photon energies of up to 100 keV, penetration depths in the millimetre range are realized and macroscopic volumes (mm³) can be investigated. Furthermore the photon flux of synchrotron sources is several orders of magnitude higher compared to laboratory tubes. Consequently in-situ measurements during a heat treatment process can be performed. Using the example of the standardized multiphase TRIP steel HCT690T, a microstructural investigation with high energy synchrotron X-ray radiation is discussed and compared to established diffraction methods using Co-and Cu-Kα-radiation. In-situ diffraction measurements during a heat treatment are exemplarily shown.
The Crystal Structure of the β’-Phase Including Ag in Al-Mg-Si-Ag Alloy
Authors: Nakamura Junya , Matsuda Kenji , Sato Tatsuo , Marioara Calin D. , Andersen Sigmund J. , Holmestad Randi , Ikeno Susumu
Published: December 2011

In the present work, b’ phase in alloys Al -1.0 mass% Mg2Si -0.5 mass% Ag (Ag-addition) and Al -1.0 mass% Mg2Si (base) was investigated by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) to understand the effect of Ag addition. The b’ phase is rod-shape with the longest direction parallel to <001>Al. HRTEM images and SAED patterns obtained along the direction were similar for the b’ phase in both alloys. The unit cell of b’-phase in Ag-addition alloy is hexagonal with the same c-axis dimension as the Ag-free b’, but shorter a-axis. Ag was found in the composition of the rod-shaped precipitates in Ag-addition alloy by energy dispersive X-ray spectroscopy (EDS). In addition, the distribution of Ag was investigated by energy filtered mapping and high annular angular dark field scanning transmission electron microscopy (HAADF-STEM). The Ag-containing atomic column was observed in every b’ unit cell, and the unit cell symmetry is slightly changed as compared with the Ag-free b’. The Ag-containing b’ rods have complicated domain structures. The interfaces of these particles are enriched with Ag atoms that occupy the lattice positions in the Al matrix. The occupancy of the Ag-containing atomic columns seem to vary both inside particles, as well as at the interfaces.
Effects of Hot-Forging Process on Combination of Strength and Toughness in Ultra High-Strength TRIP-Aided Martensitic Steels
Authors: Kobayashi Junya , Sugimoto Koh Ichi , Arai Goro
Published: December 2011

Recently developed ultra high-strength low alloy transformation-induced plasticity (TRIP)-aided steel with martensitic lath structure matrix or "TRIP-aided Martensitic steel; TM steel" possesses a high impact toughness. In this study, to apply the TM steel to some hot-forging parts, the effects of hot-forging on microstructure, retained austenite characteristics, tensile properties and toughness in the TM steels with chemical composition of 0.3-0.4%C, 1.5%Si, 1.5%Mn, 0.002%B, 0.02Ti, 0.05Nb (mass%) were investigated. The hot forging brought on an excellent combinations of tensile strength of 1500-2000 MPa or 0.2% offset proof stress of 1200-1560 MPa and Charpy impact absorbed value of 35-80 J/cm2 when partitioned at 250-350°C after quenching in oil. The combinations exceeded so much those of the conventional quench and tempering structural steels. From examinations of microstructure and retained austenite characteristics, it was found that the excellent combinations are mainly caused by (i) refined and uniform martensitic lath structure matrix with a small amount of carbide, (ii) increasing narrow martensite with high dislocation density and (iii) the increased stability of retained austenite, resulting from the FQP process.
Systematic Approach to Clarify the Mechanism of Dynamic Transformation in Fe-6Ni-0.1C Alloy
Authors: Park Nokeun , Shibata Akinobu , Tsuji Nobuhiro
Published: December 2011

In order to study about dynamic transformation phenomenon, Fe-6Ni-0.1C alloy was hot-deformed in uniaxial compression using thermo-mechanical simulator at various temperatures ranging from 600 to 1000 °C at various strain rates from 0.001 to 1 s-1 after austenitization. As the value of Zener-Hollomon (Z) parameter increased, softening of the stress from the empirically expected value, which was extrapolated from stresses deformed at low Z value, was observed through systematical analysis of peak stresses. It suggested that this softening phenomenon was attributed to the dynamic transformation, since ferrite is softer than austenite at elevated temperature. The microstructural observation also supported that ferritic transformation occurred during compressive deformation. Even above Ae3 temperature the softening of the peak stress of austenite was still observed, which implied that dynamic ferritic transformation might occur above Ae3 temperature.
Structural Changes in a 304-Type Austenitic Stainless Steel Processed by Multiple Hot Rolling
Authors: Yanushkevich Zhanna , Belyakov Andrey , Kaibyshev Rustam
Published: December 2011

The microstructure evolution and the dynamic processes of grain refinement in a 304-type austenitic stainless steel during multiple calibre hot rolling at temperatures of 700-1000°C were studied. The structural changes are characterized by the elongation of original grains towards the rolling axis and the development of new fine grains, the mean size of which decreases with decreasing the deformation temperature. During multiple rolling at 1000°C, the new grains resulted from the development of discontinuous dynamic recrystallization involving a bulging of frequently corrugated grain boundaries. On the other hand, the new grain boundaries leading to remarkable refinement of original microstructure were developed at temperatures below 800°C as a result of continuous strain-induced reactions.
INCONEL 718 Recrystallization in the Delta Supersolvus Domain
Authors: de Jaeger J. , Solas Denis , Baudin Thierry , Fandeur Olivier , Schmitt J.H. , Rey Colette
Published: December 2011

An experimental study of compression tests at high temperature and different engineering strains was carried out on INCONEL 718 above the delta phase solvus. The objective is to investigate the mechanical behaviour in relation with the microstructure evolution. After deformation the samples were quenched with helium gas to avoid metadynamic recrystallization (MDRX). The quench efficiency is discussed by microstructural and hardness comparison. During forging process and without MDRX, there is generally a competition between deformation and dynamic recrystallization state (DRX) i.e. a dependence on dislocation density increase and dislocation annihilation, respectively. To investigate this competition, samples are characterized at different scales by EBSD method to determine local texture and grain size and by TEM to understand the dislocation evolution and determine the nucleation mechanism. In parallel, a numerical model using a three-dimensional finite element model of crystalline plasticity (CristalECP) has been developed in ABAQUS™ finite element code and coupled with a Recrystallization Cellular Automaton (CA_ReX). Results of forging process simulations are compared to those of experimental studies presented before and then discussed in terms of evolution.
Microstructural Evolution of Compacted Graphite Iron under Thermo-Mechanical Fatigue Conditions
Authors: Ghodrat S. , Janssen M. , Petrov Roumen H. , Kestens Leo , Sietsma Jilt
Published: December 2011

Cast iron components in combustion engines, such as cylinder blocks and heads, are exposed for long periods of time to elevated temperatures and subjected to large numbers of heating and cooling cycles. In complex components, these cycles can lead to localized cracking due to stresses that develop as a result of thermal gradients and thermal mismatch. This phenomenon is known as Thermo-Mechanical Fatigue (TMF). Compacted Graphite Iron (CGI) provides a suitable combination of thermal and mechanical properties to satisfy the performance of engine components. However, TMF conditions cause microstructural changes, accompanied by the formation of oxides at and close to the surface, which together lead to a growth in size of the cast iron. These microstructural changes affect the mechanical properties and accordingly the thermo-mechanical fatigue properties. The aim of this research is to provide insight into the microstructure evolution of CGI, with its complex morphology, under TMF conditions. For this, optical and scanning electron microscopy observations are made after cyclic exposure to air at high temperature, both without and with mechanical loading. It was found that the oxide layers, which develop at elevated temperatures, crack during the cooling cycle of TMF. The cracking results from tensile stresses developing during the cooling cycle. Therefore, paths for easy access of oxygen into the material are formed. Fatigue cracks that develop also show oxidation at their flanks. In order to quantify the oxide layers surrounding the graphite particles, Energy Dispersive X-Ray Analysis (SEM-EDX) and Electron Probe Micro Analysis (EPMA) are used.
Tribological Characterization of Electroless Nickel-Boron Coatings
Authors: Vitry Véronique , Kanta Abdoul Fatah , Sens Adeline , Delaunois Fabienne
Published: December 2011

Nanocrystalline electroless nickel-boron deposits (on steel substrates) were submitted to heat treatment under non-reactive atmosphere or to nitriding to enhance their properties. Two different nitriding processes were used on the samples: one classical industrial process under an ammonia-based atmosphere and a novel, environment friendly treatment under a reduced pressure, nitrogen-based, atmosphere. The mechanical and tribological properties of the as-deposited and treated samples were investigated by various methods including nanoindentation and scratch tests. Their structural properties were also studied. The hardness of the deposits increased from 900 to 1250 hv100due to optimal crystallization after the heat treatment and was further enhanced up to 1600 hv100after nitriding. The scratch tests resistance of the coatings was good in both as-deposited conditions as well as after post treatment.
Fatigue Crack Propagation Rates and Local Texture Relationship in 2099-T83 Al-Li Alloy
Authors: Goma Franck Armel Tchitembo , Larouche Daniel , Blais Carl , Gauvin Raynald , Boselli Julien , Bois-Brochu Alexandre , Brochu Mathieu
Published: December 2011

An integrally stiffened panel (ISP) made from extruded 2099-T83 Al-Li alloy was subjected to fatigue loadings to investigate the influence of both the local texture and grain structure on fatigue crack propagation (FCP) behavior. The microstructure was mainly unrecrystallized. Grains were mostly layered in the web and fibrous in the other locations. Fiber texture components were present in the stiffener locations, and a rolling-type texture in the web. Resistance to FCP decreases as the local aspect ratio increases. Changes in FCP rates in the web, stiffener base and stiffener web were consistent with the microstructural features and texture. The stiffener cap with a strong fiber texture similar to that of the stiffener base exhibited a lower resistance to FCP, suggesting that the influence of the texture is convoluted in the stiffener cap by the markedly different grain structure. Therefore, FCP behavior in this alloy appears to be governed by both texture and grain structure.
Nafion-Peptized Laponite Clay Nanocomposite Membrane for PEMFC
Authors: Mishra Ananta Kumar , Bae Seon Hyeong , Kim Nam Hoon , Lau Kin Tak , Lee Joong Hee
Published: December 2011

Nafion-clay nanocomposite membrane has been prepared by dispersing unmodified and acid activated Laponite XLS in Nafion 20% dispersion. The resulting membranes possess better proton conductivity and mechanical strength as compared to the virgin membrane. Acid activation of the nanoclay leads to thein-situgeneration of H3PO4by the hydrolysis of the peptizer present on the surface of the nanoclay. Thein-situgenerated H3PO4helps in improving all the technical properties of the nanocomposite including the water uptake and proton conductivity of the nanocomposite, containing acid activated clay compared to the nanocomposite, containing unmodified clay. The maximum proton conductivity of 270.2 mS/cm is achieved at 110 °C for the nanocomposite membrane containing 3% acid-activated Laponite compared to 136.2 mS/cm for the virgin Nafion. Keywords: Nafion, clay, nanocomposite, peptizer, polymer electrolyte membrane fuel cell (FEMFC), proton conductivity, membrane
Characterization of Polystyrene (PS)/Organomodified Layered Double Hydroxide (OLDH) Nanocomposites Prepared by In Situ Polymerization
Authors: Sahu Balakrushna , Pugazhenthi G.
Published: December 2011

PS/LDH nanocomposites were synthesized via in-situ polymerization technique using styrene monomer with toluene as a solvent. A series of LDHs (Mg-Al, Co-Al, Ni-Al, Cu-Al, Cu-Fe and Cu-Cr LDHs) was first prepared from their nitrate salts by co-precipitation method. The above prepared, pristine LDHs were organically modified using sodium dodecyl sulfate (SDS) to obtain organomodified LDHs (OLDH). Then, PS nanocomposites containing 5 wt.% OLDHs were prepared by in-situ polymerization method. The structural and thermal properties of LDHs and corresponding nanocomposites were characterized by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA). The absence of OLDH peak (003) in the XRD patterns of PS/OLDH nanocomposite confirms the formation of exfoliated nanocomposites. The presence of sulfate groups in the modified LDHs is confirmed by FTIR analysis. The appearance of new peaks in the FTIR spectra in the region of 3400-3500 cm-1, 1670-1680 cm-1and 1200-1260 cm-1for O-H stretching, H-O-H vibration and stretching vibration of sulfate, respectively indicate the existence of LDHs in the PS/OLDH nanocomposites. The entire exfoliated PS/OLDH nanocomposites exhibit enhanced thermal stability relative to the pure PS. When 50% weight loss is selected as point of comparison, the decomposition temperature of nanocomposites is about 3-5oC higher than that of pure PS.
Developing Corrosion-Resistant Joints Applied in the Plate Heat Exchanger
Authors: Shu C.H. , Hsu H.W. , Yeh T.Y. , Chen W.S. , Shiue R.K.
Published: December 2011

The manufacturing of plate heat exchangers is much more difficult than that of making traditional heat exchangers. The demand of increased corrosion resistance, avoiding Cu ion contamination, resisting to high-temperature resulting from various applied environments makes the traditional Cu brazed 316 stainless steel (316SS) plate heat exchanger fail to satisfy certain applications. Corrosion-resistant brazed 316SS plate heat exchangers are successfully developed using two commercially available Ni-based brazing foils, and they are valuable for industrial applications.
The Extrinsic Influence of Tool Plunge Depth on Friction Stir Welding of an Aluminum Alloy
Authors: Kandasamy K. , Kailas Satish V. , Srivatsan Tirumalai S.
Published: December 2011

The axial force during friction stir welding is sensitive to plunge depth of the tool and is one of the prime factors, which exercises control over heat generation during welding. Consequently, the plunge depth for a given tool rotation speed, traverse speed, material and test machine needs to be optimized so as to get a defect-free weld. In this paper, we present and briefly discuss the results of an elaborate and enriching investigation aimed at understanding the extrinsic influence of plunge depth of the tool on weld formation in aluminium alloy 7020-T6 for a range of rotation rate and traverse speed and using two different tools. The critical need for use of a scientific approach to optimize plunge depth for a given tool material and test machine in fewer number of steps is emphasized. Key Words: Friction Stir Welding, Tool Plunge, Rotation speed, Traverse speed, Aluminium Alloy 7020
Effect of h-BN Content on the Sintering of SS316L/h-BN Composites
Authors: Mahathanabodee S. , Palathai Tippaban , Raadnui S. , Tongsri Ruangdaj , Sombatsompop Narongrit
Published: December 2011

In this work, the three compositions of hexagonal boron nitride (10, 15 and 20 vol. %)-embedded 316L stainless steel (SS316L/h-BN) composites were prepared by a conventional powder metallurgy technique and then sintered at varying temperatures of 1100 to 1250°C for 60 min in H2 atmosphere. The h-BN content and sintering temperature were found to affect the microstructure and hardness of the composites. The hardness decreased with increasing h-BN content and was improved by increasing the sintering temperature. Microstructure results revealed that the boride phase was formed at the grain boundary at the sintering temperature higher than 1150°C and the boride phase formation was observed to transform the h-BN in the composites.
Synthesis and Characterization of Al-Alloy/SiCp Nanocomposites Employing High Energy Ball Milling and Spark Plasma Sintering
Authors: Bathula Sivaiah , Anandani R.C. , Dhar Ajay , Srivastava A.K.
Published: December 2011

This study reports the synthesis and characterization of Al-alloy/SiCpmetal matrix nanocomposite, synthesized using high energy ball milling followed by sintering employing spark plasma sintering (SPS). In the present investigation, Al 5083 alloy powder (15 μm) and 10wt.% SiC particulates (~20 nm) were milled in a high-energy planetary ball mill to produce nanocrystalline Al-alloy/SiC nanocomposite powders. X-ray diffraction analysis (XRD) was carried out for milled and un-milled powder and it was observed that, as the time of milling increased, the crystallite size of Al-alloy matrix decreased sharply. The average crystallite size of Al-matrix from XRD analysis was observed to be ~ 25 nm after 15 h of ball milling. Ball milled nanocomposite powders were consolidated and sintered employing SPS at a temperature range of 500°C with a heating rate of 300°C/min and the total sintering cycle was completed in 8 min. The mechanical properties were found to substantially increase after sintering employing SPS. Morphology of as received (un-milled) powders, milled powders and sintered nanocomposites were investigated by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). The mechanical property evaluation of the sintered nanocomposite was done by measuring nanoindentation, micro-hardness and compressive strength.
Multi-Functional Soft Smart Materials and their Applications
Authors: Leng Jin Song
Published: December 2011

Stimulus-active polymers can change their shapes with respect to configuration or dimension upon exposure to a particular stimulus such as heat, electricity, light, magnetic, solvent and pH value. These unique characteristics enable stimulus-active polymers to be used in a myriad of fields, including clothing manufacturing, automobile engineering, medical treatment, and aerospace engineering. Stimulus-active polymers can be applied in smart textiles and apparels, intelligent medical instruments and auxiliaries, artificial muscles, biomimetic devices, heat shrinkable materials for electronics packaging, micro-electro-mechanical systems, self-deployable sun sails in spacecrafts, miniature manipulator, actuators and sensors, and many more. This paper presents some recent progress of soft smart materials and their applications. Special emphasis is focused upon shape memory polymer (SMP), electro-active polymer (EAP) for aerospace engineering such as space deployable structures and morphing aircraft, which has highlighted the need for development of these materials. A detailed overview of development in these smart soft materials, of which the undergoing and future applications are used in adaptive structures and active control, is presented. The paper concludes with a short discussion for multi-functional soft smart materials and their composites that are expected to extend the range of development and applications available to the related researches and engineers.
Study on Mechanical Properties of 2024 Al Sheet Treated by SMAT
Authors: Cheung K.P. , Silvanus J. , Shi San Qiang , Lu Jian
Published: December 2011

SMAT is applied as an innovation surface enhancement technology to introduce compressive stress in metallic materials. The strengthening effects of SMAT in mechanical properties were investigated on aluminium alloy. The yield strength obtained under tensile test had significant improvement which may achieve up to 440 MPa. In this paper, the experimental setup and results will be briefly described. Tensile properties measured before and after SMAT at ambient temperature. Results show that the highest strength that can be attained is 544 MPa by SMATed sheet of 1 mm thickness for 15 minutes and 518 MPa for the 2.5 mm one SMATed with 45 minutes, with the desirable ductility. The present study demonstrates this high strength and corrosion resistance aluminium alloy can be a potential candidate for applications in aviation industries.
Electrospun Nanofibre Cores Containing Graphene Oxide for Sandwich Films: Manufacturing and Analysis
Authors: Rao S. , Liu D. , Jaiswal P. , Ray Sudip , Bhattacharyya Debes
Published: December 2011

The motivation for the need of small-scale devices has made thin films technologically important in the recent years. They have found applications in broad fields, such as microelectronic integrated circuits, magnetic information storage systems, optical coatings and wear resistant coatings. However, the mechanical performance of these materials tends to depend on fabrication and post-processing parameters. With the intent of improving the mechanical properties of the films, a relatively novel concept of sandwich composite films has been tried in this research. Poly-methyl methacrylate (PMMA) and Graphene Oxide (GO) have been used to manufacture the sandwich films, where PMMA films have served as the facings and electrospun PMMA/GO nanofibre mat forms the sandwich core. Dimethylformamide (DMF) and Tetrahydrofuran (THF) solvents are used in suitable proportions to dissolve PMMA, and then GO is added to this solution to obtain a uniform suspension of PMMA/GO for electrospinning. The mechanical and functional properties depend on the fibre quality and their distributions in the mat, which in turn depends on the concentration of the solution. Therefore, design of experiments based on mixture analysis was used to identify the solution concentration for obtaining uniform fibre diameters and their distribution throughout the electrospun core. The analysis suggested 23% PMMA and 2% GO concentrations in the solution would give uniform fibre diameters and dispersion throughout the mat.
Finite Element Modeling for Hot Forging Process of AISI 4340 Steel
Authors: Sanrutsadakorn Apichat , Uthaisangsuk Vitoon , Suranuntchai Surasak , Thossatheppitak Borpit
Published: December 2011

Hot forging is a common, but important manufacturing process in metal forming industries. Forming at high temperature, flow stress of material decreases and thus lower load is required. Furthermore, mechanical properties of material regarding its microstructure characteristics can be improved according to heating and cooling conditions. Hot forging process for a spacer wheel made of steel AISI 4340 was investigated by means of FE simulation. Initially, hot compression test was performed using a thermo-mechanical simulator for determining flow curves. Different temperatures and strain rates within the process range were considered. A Zener-Hollomon parameter was applied to describe the experimentally obtained flow curves. To verify accuracy of the FE simulations, multi-step hot compression test was carried out at different forming temperatures. Subsequently, force development and final shape calculated for the investigated part were analyzed. Reliability of the FE results was significantly influenced by the defined flow curve or hot deformation behavior of material.
Magnesium Matrix Composites: State-of the-Art and what’s the Future
Authors: Dieringa Hajo , Kainer Karl Ulrich
Published: December 2011

A huge number of different process types are in use to produce magnesium-based composites. Depending on the reinforcement type, all the processes can be subdivided into solid state or powder metallurgical (PM) and liquid phase or ingot metallurgical (IM) processes. In this paper we will focus on ingot metallurgy processes. These liquid state processes result quite often in a very good interface of reinforcement with the magnesium matrix. The liquid processes can be further subdivided into infiltration techniques, casting processes and spray deposition. Those are the most inexpensive processing technologies for discontinuous, reinforced magnesium-based composites. When produced using melting processes, nanoparticle-reinforced magnesium composites are expected to improve in strength, due to the grain refinement described in the Hall-Petch relation. When an isotropic distribution of nanoparticles is achieved, the composites are additionally expected to be Orowan-strengthened. That is why nanosized reinforcements are expected to represent the future for improving the properties of magnesium-based metal matrix composites.
Welding Heat Transfer Analysis Using Element Free Galerkin Method
Authors: Das Raj , Bhattacharjee K.S. , Rao S.
Published: December 2011

Mesh-less methods belong to a new class of numerical methods in computational mechanics and offer several advantages over the conventional mesh-based methods. They enable modelling of processes involving high deformation, severe discontinuities (e.g. fracture) and multiple physical processes. These types of situations are usually encountered in arc welding, rendering its modelling suitable via mesh-less methods. In this paper, a mesh-less Element Free Galerkin (EFG) method has been developed to model the heat transfer during welding. The results predicted by the EFG method are found to be in close agreement with those obtained by the finite element method and those observed in welding experiments. This demonstrates the effectiveness and utilities of the EFG method for modelling and understanding the heat transfer processes in arc welding.
Flame Retardancy, Thermal Stability, and Mechanical Properties of Sisal Fiber/Organoclay/Polypropylene Composites
Authors: Chanprapanon Wichuda , Suppakarn Nitinat , Jarukumjorn Kasama
Published: December 2011

Composites based on polypropylene (PP) and sisal fiber (SF) were prepared by melt blending. Sisal fiber content was 30 phr. Organoclay (OMMT; Cloisite®30B) (1-7 phr) was incorporated into the composites. In addition, maleic anhydride grafted polypropylene (MAPP) was used as a compatibilizer to enhance the interfacial adhesion between PP matrix and sisal fiber and also to improve the dispersion of the organoclay in PP matrix. The addition of OMMT had insignificantly affected mechanical properties of SF/PP composites. However, flame retardancy and thermal stability of SF/PP composites were improved dramatically with the presence of OMMT.