bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Physical and Mechanical Properties in Ceramics Composites Si3N4–CTR–AlN and Si3N4–Y2O3–AlN
Authors: Baldacim Sandro Aparecido , Silva Olivério Moreira Macedo , dos Santos Claudinei , Silva Cosme Roberto Moreira
Published: March 2009

The important factor to consider for successful ceramics composites development is the need of matching the whiskers and matrix characteristics, taking into account the chemical compatibility of the sintering aids utilized. The purpose of this work was to analyze and compare use of rare earth concentrate (CTR) and yttrium oxide, as sintering aids, and its influence in the densification and physical/mechanical properties of hot pressed and sintered Si3N4-SiC(w). The CTR powder materials present high yttrium oxide percentage and its production is cheaper than the additives usually used in ceramic materials, such as Y2O3. For physical and mechanical properties evaluation, specific mass, crystalline phases, micrographs analysis, microhardness and fracture toughness were measured, showing similar results between the two sintering aids. Therefore, this study shows the possibility of obtaining low processing cost products with the use of rare earth concentrate. Meanwhile, more characterization steps are necessary for analyzing its behavior at elevated temperatures.
Composites of Portland Cement and Natural Polymers
Authors: Bezerra Ulisses Targino , Martinelli Antonio Eduardo , Melo D.M.A. , Henrique D.M. , Rodrigues E.M. , Lima F.M.
Published: March 2009

The tensile strength of Portland cement may be increased by additional reinforcement. This is usually accomplished by means of steel rods, fibers or particles, which are mixed to the slurry. In an attempt of increasing toughness and tensile strength of hardened cement pastes, the present work describes the behavior of composites consisting of Portland reinforced by natural polymer particles for oil well cementing. The main purpose of the study was to select plastic and environmentally friendly powdered materials capable of filling the typical porosity developed on hardened Portland cement. Preliminary results suggested that the tensile strength of plain Portland hardened slurries could be increased by as much as 40% by adding 10% of reinforcement.
Chemical Vapor Densification Process of Carbon Fiber Substrates
Authors: Kajita Tetunori , Pardini Luiz Claudio , de Melo Francisco Cristóvão Lourenço
Published: March 2009

The densification of carbon fiber substrates by chemical vapor deposition (CVD) is a process quite used since the fifties, for manufacturing carbon reinforced with carbon fiber composites (CRCF). The process is based in thermal decomposition of a gas which contains carbon in its molecules and the resulting pyrolytic carbon is continually deposited onto de carbon fiber substrate. For this experiment the substrate material was made of carbon fiber felt. The deposition was performed by isothermal process at atmospheric pressure and at temperature of 1050 oC. Methane (CH4) gas was used as carbon bearer and nitrogen (N2) as the carrier gas. Different volumetric ratio of N2 and CH4 (N2:CH4) were used in order to get an optimum densification of the substrate. Optical and electron scanning microscopy and density measurements were used to characterize the impregnated material. An increase in ratio of N2 and CH4 increase the overall deposition for the same time interval.
Study of the Potentiality of Residue from Kaolin Industry as Ceramic Raw Material to Produce Porcelanate Gres
Authors: Ramalho M.A.F. , de Lima Santana Lisiane Navarro , Neves Gelmires Araújo , Lira Hélio Lucena
Published: March 2009

The recycling of industrial residues has being intensified all over the world, mainly due to the increase of the impact to the environment, and the growing volume of solid residues that put in risk the public health and degrade the natural resources. So, the aim of this work is to study the potentiality of the residue from kaolin industry, as ceramic raw material to produce porcelanate gres. A composition was formulated, mixed and forming by pressing (from 30 MPa to 50 MPa). After, it was sinterized at temperatures of 1180°C, 1200°C, 1220°C and 1240°C. The samples were submitted to physical and mechanical tests and characterized by X-ray diffraction and scanning electron microscopy. The preliminary results from physical and mechanical properties showed that the residue can be used to produce porcelanate gres according to Brasilian Norms (NBR 13818), at temperatures of 1220°C and 1240°C.
Microstructural Evolution during Sintering of the P/M Blended Elemental Ti-5Al-2.5Fe Alloy
Authors: Siqueira Rodrigo P. , Sandim Hugo Ricardo Zschommler , Henriques Vinicius André Rodrigues , Lins J.F.C.
Published: March 2009

The alpha-beta Ti-5%Al-2.5Fe (wt-%) alloy was developed as a cost-effective option to replace the traditional Ti-6%Al-4%V alloy in the manufacture of surgical implants because of its larger biocompatibility (V-free alloy). Samples of this alloy were prepared using the blended elemental (BE) technique. The isochronal sintering of the cold pressed compacts was carried out at 700, 1000, and 1400°C in vacuum. In this work, the preliminary results of the behavior of elementary powders during sintering and the corresponding microstructural evolution are shown. The alloy was characterized by means of scanning electron microscopy (SEM) in the backscattered mode, X-ray diffraction (XRD), energy-dispersive spectrometry (EDS), and density measurements. The results indicate that the homogenization of the alloy is diffusion-controlled. Non-equilibrium Ti-Al phases as well as Fe-Al compounds were identified in samples sintered at lower temperatures (700oC). With increasing temperature, homogenization of the alloy takes place and a structure consisting of coarse plate-like alpha and intergranular beta is present.
Influence of the Granulometry of Organic Matter Ashes from Municipal Solid Waste on the Properties of Vitrified Ceramics
Authors: Gadioli Monica Castoldi Borlini , Santos B.C. , Conte R.A. , Pinatti Daltro Garcia , Vieira Carlos Maurício Fontes , Monteiro Sérgio Neves
Published: March 2009

This work studies the influence of the granulometry of organic matter ashes from the municipal solid waste (MOL) on the mechanical properties of vitrified ceramics. Mixtures of clay with additions of the MOL ashes were prepared as vitrified ceramics. The degree of immobilization of the potentially toxic metals (PTM) contained in the ashes was then evaluated. Samples of a sedimentary clay with 13.5% of MOL ashes with granulometry, 35 and 200 mesh, were uniaxially pressed at 18 MPa and sintered at 1200°C. Results from 3- point flexural resistance and water absorption tests showed that the reduction in the particle size of the MOL ashes increased the mechanical resistance to 45 MPa while the water absorption reached 0.8%. These results and the high degree of immobilization of the PTM qualify the ceramic vitrification as an alternative to the final disposal of the MOL.
Synthesis and Characterization of NiO-8YSZ Powders by Coprecipitation Route
Authors: Yoshito Walter Kenji , Ussui Valter , Lazar Dolores Ribeiro Ricci , Pascoal José Octavio A.
Published: March 2009

Nickel oxide – 8 mol% yttria stabilized zirconia (NiO-8YSZ) powders containing 25 to 75 wt% of NiO were prepared by coprecipitation. The entire process includes the reaction of metals aqueous chloride solutions (heated at 95 oC) with ammonium hydroxide, washing steps of the resulting gel, butanol azeotropic distillation treatment to prevent the formation of hard agglomerates, drying, calcination and ball milling. The yield of precipitation of metals was determined by inductively coupled plasma atomic emission spectroscopy analysis (ICP-AES). Powders were characterized by X-ray and laser diffraction, infrared analysis, gas adsorption (BET) and scanning electron microscopy. It was observed that zirconium and yttrium hydroxides are easily precipitated in alkaline medium, while nickel precipitation yield is in the range of 80 to 95% due to the formation of soluble complexes. NiO appears as a second phase in synthesized powders and contributes to decreasing of specific surface area and agglomerate mean size.
Modeling of the Microstructural Evolution and Mean Flow Stress during Thin Slab Casting/Direct Rolling of Niobium Microalloyed Steels
Authors: Siciliano Fulvio , Leduc L.L.
Published: March 2009

Mill logs obtained from the Hylsa CSPTM (thin slab casting/direct rolling – TSC/DR) mill were examined so that the mean flow stresses at each pass were calculated using the Sims equation modified to take into account the forward slip ratio, the redundant strain and the work roll flattening. The mean flow stresses were then compared to predicted values obtained from a model. The microstructures during the CSP process were predicted by a mathematical model which was initially derived for conventional slab/roughing mill/hot strip mill (HSM) processing route. The adapted model takes into account the deformation of the as-cast structure in the finishing CSP mill, by using particular microstructural equations to calculate the softening kinetics and grain sizes. The main metallurgical features such as the occurrence of Nb(C,N) precipitation, the softening mechanism which takes place (static or metadynamic recrystallization) as well as the strain accumulation between passes were calculated. The mean-flow-stress results obtained from the calculations are in good agreement with the mill data. The present analysis indicates that it is possible to produce fine-grained microalloyed steels with homogeneous microstructure in thin slab casting/direct rolling processing.
Processing of Niobium Microalloyed API Grade Steel on a Thin Slab Plant
Authors: Klinkenberg Christian , Hensger K.-E.
Published: March 2009

The use of thin slab casting and direct rolling is well suited for the production of niobium microalloyed low-carbon high strength linepipe grades. The slabs have excellent surface quality. Thermomechanical processing by controlling hot work hardening and softening processes of austenite and its polymorphic transformation into ferrite results in a powerful microstructure refinement. This is a sound basis for setting high strength, combined with excellent ductility and toughness.
Transformation Induced Plasticity (TRIP) Effect Used in Forming of Carbon CMnSi Steel
Authors: Kliber Jiří , Mašek Bohuslav , Zacek Ondrej , Staňková H.
Published: March 2009

Transformation induced plasticity (TRIP) steel combines high strength and high ductility that makes it particularly suitable for forming. Martensite within a ferrite matrix is usually obtained either by continuous casting of slabs followed by hot rolling (which is the fastest method, hence the most economical one, producing, however, relatively thick products) or by the continuous casting of slabs followed by hot rolling, cold rolling and annealing (the method used for thin products). High cooling rates, low coiling temperatures and low reduction during hot deformation were generally found to suppress the formation of polygonal ferrite and promote the presence of retained austenite. This paper focuses on development and modifications of two CMnSi-based TRIP steels with 0,23 % C;1,4 % Mn; 1,9 % Si; ( 0,08 % Nb) by means of laboratory thermomechanical processing. Description of experimental devices for the analysis of transformation plasticity under tensioncompression loading is given. Experiments were carried out on the simulator for thermaldeformation cycles SMITWELD and TANDEM was used for thermomechanical processing on the laboratory rolling mill. The maximum volume fraction of retained austenite and the resulting optimum combination of tensile strength and ductility were achieved in testing heats. Special attention was paid to volume fraction changes of single phases and to changes in morphology of phases. The results suggest that rather short isothermal bainite transformation times are sufficient to obtain TRIP microstructure. The influence of parameters of thermomechanical processing such as the amount of strain, forming temperature and austenitization time and temperature on microstructures of TRIP steels were evaluated.
Influence of Composition and Processing Conditions on Mechanical Properties and Fish-Scale Resistance of Microalloyed Steels for Double-Face Vitreous Enamelling
Authors: Schöttler Joachim , Flaxa V. , Hulka Klaus
Published: March 2009

Hot- and cold-rolled steel sheets are the most important substrate materials for enamelling applications. Currently, industry is actively seeking ways to widen the area of application of hotrolled steel sheets for double-face enamelling. Another important task is search for new steel compositions that might substitute for currently used open-coil annealed, cold-rolled steel sheet for direct white enamelling applications. The purpose of this research project was the investigation of influence of chemical composition and processing conditions of several microalloyed steels on
mechanical properties and fish-scale resistance of hot and cold rolled sheets. The results show that a high fish-scale resistance of the hot-rolled steel is achieved by creating a high volume fraction of fine precipitates (nitrides, carbides, carbonitrides, sulphides, etc.). By partial replacement of titanium with other carbide and nitride forming elements, such as niobium and/or boron, the suitability of cold-rolled IF steels for white direct-on enamelling can be remarkably improved without open-coil annealing. However, the processing conditions have to be tuned to ensure high fish-scale resistance without impairing formability.
Development of Low Carbon Microalloyed Ultra High Strength Steels
Authors: Ghosh A. , Mishra Brajendra , Chatterjee Subrata
Published: March 2009

In the present study HSLA steels of varying carbon concentrations, alloyed with Mn, Ni, Cr, Mo, Cu and micro-alloyed with Nb and Ti were subjected to different finish rolling temperatures from 850oC to 750oC in steps of 50oC. The microstructure of the steel predominantly shows martensite. Fine twins, strain induced precipitates in the martensite lath along with e-Cu precipitates are observed in the microstructure. With an increase in carbon content the strength value increases from 1200MPa UTS to 1700MPa UTS with a negligible reduction in elongation. Impact toughness values of 20-26 joules at room temperature and −40oC were obtained in sub-size samples.
Low Temperature Solubility Limit of Copper in Iron
Authors: Perez Michel , Perrard Fabien , Massardier-Jourdan Véronique , Kleber Xavier , Schmitt Vincent , Deschamps Alexis
Published: March 2009

The solubility limit of copper in iron at temperature lower than 700°C is not precisely
known because copper diffusion is too slow to reach an equilibrium with classical experimental techniques involving long range diffusion. However, fine precipitation of copper can lead to an equilibrium in a reasonable ageing time. Hence, coupling ThermoElectric Power and Small Angle X-ray Scattering techniques leads to a precise estimation of this solubility limit in the temperature range 500°C-700°C. Values obtained are confirmed by Tomographic Atom Probe and give results much higher than what is usually extrapolated from high temperature experiments.
A Thermodynamic Database for Fe-Cr-Mn-Ni-Ti-S-C-N System
Authors: Oikawa Katsunari , Mitsui Hajime , Ishida Kiyohito
Published: March 2009

A database for thermodynamic information of sulfides and carbo-sulfide in steels has been developed, where the thermodynamic properties of the relevant constituting sub-system of the complex system have been assessed by the CALPHAD (Calculation of Phase Diagrams) approach. The utility of this database is demonstrated in examples of phase diagram calculations of low carbon steels and stainless steels. The calculated results are in good agreement with experimental data. The developed thermodynamic database would be useful in predicting the formation of sulfides and carbo-sulfides in the commercial steels.
Grain Refinement by Rapid Transformation Annealing of Cold Rolled Low Carbon Steels
Authors: Álvarez P. , Lesch C. , Bleck Wolfgang , Petitgand Hélène , Schöttler Joachim , Gil Sevillano J.
Published: March 2009

A novel thermal treatment, rapid transformation annealing (RTA), has been applied to six different cold rolled low-carbon (LC) steel sheets with the aim of refining their microstructure. The process involves rapid heating to just above the austenite (g) to ferrite (a) transformation temperature and subsequent rapid cooling to room temperature. Grain sizes around 2 µm in two different Nb-Ti HSLA steels, 5 µm in a Ti-LC steel and 6 µm in a plain LC (0.037%C) steel have been produced using fast cooling rates (200°C/s). Non-equiaxed structures are obtained in a Nb-Ti HSIF steel and in a plain LC (0.135%C) (CM) steel due to their higher Mn content. However, very fine equiaxed grains (2 µm) are obtained by rapid intercritical annealing (RIA) in the CM steel. Irrespective of the microalloying concept, the grain growth of recrystallized a grains before their transformation was inhibited in CM and in both HSLA steels. This inhibition is connected with the overlapping of a recrystallization and a-g transformation processes which is essential in order to achieve extreme grain refinement either by RTA or RIA.
Parameters Influencing the Bake Hardenability of Microalloyed ULC Steels
Authors: Al Shalfan W.A. , Speer John G. , Matlock David K.
Published: March 2009

Ti-V and Ti-Nb bake hardenable Ultra Low Carbon (ULC) steels are used to produce hot dip zinc coated steels for automotive applications. An important factor influencing the bake hardenability in such microalloyed ULC steels is the level of solute carbon available to diffuse for pinning dislocations during baking. The level of solute carbon must be controlled carefully during annealing of the steel in the ferritic region. Therefore, this paper summarizes highlights of research conducted to study the effects of chemical composition and annealing temperature (in the ferrite region) on the precipitation (or dissolution) of NbC and VC using a variety of Ti-Nb and Ti-V ULC steels. Carbon diffusivity is another factor that could also influence the bake hardenability through controlling the aging and baking kinetics. Therefore, the paper presents highlights of internal friction measurements performed to assess effects of microalloying elements (Nb,V) and some commonly used solid solution strengthening elements (Mn, P) on carbon diffusivity measured using the internal friction technique.
Diffusion Reactivity between Zinc Plate Layer and Nanocrystalline Surface Layer of IF Steel by Near Surface-Severe Plastic Deformation
Authors: Minamino Yoritoshi , Tsuji Nobuhiro , Koizumi Yuichiro , Nakamizo Y. , Sato M. , Shibayanagi Toshiya , Naka Masaaki
Published: March 2009

The effect of near surface-ultrafine grain (NSUFG) layer with grain size of about 90nm on the solid reaction between Ti-added ultra-low carbon interstitial free steel sheet and electroplated zinc layer (ZP) was basically investigated at 473K and 573K, in comparison with the reactions of the coarse grains IF steel sheet (CG-IF) and the ZP. The NSUFG structure dramatically changes the reactions between ZP and IF steel, as follows; (1) the incubation times for the formation of reaction layers, pseudo-z-phase, are quite shorter for the NSUFG/ZP reactions than the CG/ZP ones, (2) in the early stage of annealing the former has the smooth interfaces of pseudo-z-phase layers but the latter has wavier ones like a stone wall, (3) the thickness of the pseudo-z-phase layer of the former is thicker than that of the latter, (4) some cracks are observed in NSUFG layers while no crack in coarse grain IF steel, and (5) the subsequent layer appears in the reaction between pseudo-z-phase and NSUFG layers former after long annealing by the blast-like break of the interface.
Recent Development of Highly Corrosion Resistant Bulk Glassy Alloys
Authors: Asami Katsuhiko , Habazaki H. , Inoue Akihisa , Hashimoto Koji
Published: March 2009

Recent development of corrosion resistant bulk glassy alloys such as Zr-, Fe-, Ni- and Cu-base alloys were presented. It was clarified that the enrichment of cations in the passive film, which is responsible to corrosion resistance, depends on both alloy composition and environment. TEM observation also made it clear that alloys lose their advantageous properties such as corrosion resistance when they are devoid of or lose amorphous structure even in part due to low glass forming ability or heating. These findings were essentially similar to those of conventional amorphous alloys.
Coarse-Grained Molecular Modeling of Composite Interfaces
Authors: Tan Vincent B.C. , Deng M. , Tay Tong Earn
Published: March 2009

The interface of fiber and matrix strongly influences the performance and strength of fiber-reinforced composite materials. Due to the limitations of continuum mechanics at the nanometer length scale, atomistic level computer simulation has started to play an important role in the understanding of such interfacial systems. Our study focuses on a typical crosslinked interfacial system of glass-epoxy composite with the presence of silanes. To explore the mechanical properties of the interfacial network system, Coarse-grained Molecular Dynamics is used. Currently it is not possible to study mechanical properties of interfacial systems purely through ab initio molecular dynamics simulations because of the huge computational resources required. Although pure atomistic classical molecular dynamics simulations have been used to study systems comprising billions of atoms, classical MD simulation do not take into account the effects of crosslinking of molecular chains. A new force field, which combines the Lennard-Jones potential and a finiteextensible nonlinear elastic attractive potential, is proposed and incorporated in a bead-spring model to simulate glass/epoxy interfacial system with the crosslinked structure of silanes. The finite-extensible nonlinear elastic attractive potential is included to control the motion and breakage of polymer chains. Interfacial adhesion and mechanical properties were studied through the simulation of mechanically separating the interfacial system.
Selection of Proper Fatigue Model for Flip Chip Package Reliability
Authors: Shin Young Eui , Kim Yeon Sung , Kim Hyoung-Il , Kim Jong Min , Chang Kyong Ho , Farson Dave F.
Published: March 2009

There have been diverse fatigue models and approaches to properly estimate solder joint reliability. However, it is one of the most difficult problems to determine which solder constitutive models and fatigue models can be applied best. In this paper, both viscoplastic and elastic-plastic-creep solder constitutive models could be utilized to calculate accumulated inelastic response under 208 K to 423 K(-65 °C to 150 °C) thermal cycling condition. And two different fatigue models, Darveaux and creep-fatigue model were applied to find solder joints fatigue life for flip chip assembly. Moreover, each fatigue life was compared to experimental result for the validation of finite element analysis. The actual number of cycles to failure was obtained from cross sectional view of the package with SEM.
Indentation Rate-Dependent Creep Behavior of Sn-Ag-Cu Pb-Free Ball Grid Array (BGA) Solder Joint
Authors: Wang Feng Jiang , Ma Xin , Qian Yiyu
Published: March 2009

Berkovich micro-indentation tests with different loading rates have been performed on the ball grid array solder joint with a Pb-free solder, Sn-4.0Ag-0.5Cu alloy. The resulting indentation load-depth curves are rate dependent and have varying creep penetration depths during the same hold time. Creep indentation hardness and rate sensitivity have been defined from the concept of “work of indentation”. The rate sensitivity of BGA solder joint is 0.0574.
Novel Method for Diffusion Bonding Superalloys and Aluminium Alloys (USA Patent 6,669,534 B2, European Patent Pending)
Authors: Shirzadi A.A. , Wallach E.R.
Published: March 2009

A novel method for diffusion bonding metallic alloys with stable surface oxide films (e.g. nickel and cobalt base superalloys and aluminium alloys) has been developed. The stable oxides on the faying surfaces of these alloys are replaced, prior to the bonding process, with a very thin metallic layer and/or less stable oxides, using a proprietary non-chemical oxide removal method based on the use of gallium. This new method is very rapid and neither requires the use of any sophisticated equipment nor is a costly process. Bonding is then readily achieved by either solid-state or transient-liquid-phase (TLP) diffusion bonding. Using this method, bonds in nickelbase and cobalt-base superalloys with “virtually invisible” bond interfaces and bonds in aluminium alloys with strengths as high as those of the parent alloys can be produced.
The Role of Bond Coat in Advanced Thermal Barrier Coating
Authors: Narita Toshio , Hayashi Shigenari , Lang Feng Qun , Thosin Kemas Zaini
Published: March 2009

A novel diffusion barrier bond coat with a duplex layer structure, a sigma phase Re-Cr-Ni barrier and Ni aluminides as an aluminum reservoir was formed on a Ni based superalloy (TMS 82+) and Hastelloy X. The oxidation behavior of both alloys with and without the sigma- Re-Cr-Ni -phase as a diffusion barrier was investigated at temperatures of 1373K (Hastelloy X) and 1423K (TMS-82+) for up to 360ks. It was found that the Re-Cr-Ni acts as a diffusion barrier for both inward diffusion of Al and outward diffusion of alloying elements in the alloy substrate.
Microstructure and Thermal Stability of Ultra Fine Grained Mg-Based Alloys Prepared by High Pressure Torsion
Authors: Čížek Jakub , Procházka Ivan , Smola Bohumil , Stulíková Ivana , Kužel Radomír , Matěj Z. , Cherkaska V. , Islamgaliev Rinat K. , Kulyasova Olya B.
Published: March 2009

In the present work we studied microstructure of ultra fine grained (UFG) pure Mg and UFG Mg-based alloys. The initial coarse grained samples were deformed by high pressure torsion (HPT) using pressure of 6 GPa. Such deformation leads to formation of UFG structure in the samples. The severe plastic deformation results in creation of high number of lattice defects. Therefore, we used positron annihilation spectroscopy (PAS) for defect characterizations. PAS represents a well developed non-destructive technique with high sensitivity to open volume defects like vacancies, vacancy clusters, dislocations etc. In the present work we combined PAS with TEM and XRD to obtain complete information about microstructure of the UFG samples studied. We have found that microstructure of HPT-deformed Mg contains two kinds of regions: (a) ”deformed” regions with UFG structure (grain size 100-200 nm) and high number of randomly distributed dislocations, and (b) ”recrystallized” regions with low dislocation density and grain size of few microns. It indicates some kind of dynamic recovery of microstructure already during HPT processing. On the other hand, homogenous UFG structure with grain size around 100 nm and high density of homogeneously distributed dislocations was formed in HPT-deformed Mg-9.33 wt.%Gd alloy. After characterization of the as-deformed microstructure the samples were subsequently isochronally annealed and the development of microstructure with increasing temperature and recovery of defects were investigated.
Fracture Toughness in Ultra Fine-Grained Magnesium Alloy
Authors: Somekawa Hidetoshi , Mukai Toshiji
Published: March 2009

The fracture toughness was investigated using in an extruded AZ31 magnesium alloy with an initial grain size of 1.0 μm. Since the small scale yielding condition was not satisfied with the present thin thickness, the value of plane-strain fracture toughness, KIC = 27.9 MPam1/2, was measured from Stretched Zone analysis. The values of KIC in AZ31 magnesium alloys were dependent on the grain size. The grain refinement was found to be one of the improvement methods for fracture toughness in magnesium alloy.
Enhancement of Ductility and Strength through Microstructural Refinement by FSP of Nickel Aluminum Bronze
Authors: Oh-ishi Keiichiro , Zhilyaev Alexandre P. , McNelley Terry R.
Published: March 2009

Friction stir processing (FSP) is a severe plastic deformation (SPD) method that has been applied to as-cast NiAl bronze (NAB) materials, which are widely used for marine components. The thermomechanical cycle of FSP results in homogenization and refinement, and the selective conversion of microstructures from a cast to a wrought condition. The physical metallurgy of NAB is complex and interpretation of the effects of FSP on microstructure has required detailed analysis by optical and electron microscopy methods. Annealing and isothermal hot rolling have been employed to confirm microstructure-based estimates of stir-zone peak temperatures. The variation of mechanical properties was assessed by use of miniature tensile samples and correlated with microstructure for samples from stir zones of single and multi-pass FSP. Exceptional improvement in strength – ductility combinations may be achieved by FSP of NAB materials.
Simulation of Equal-Channel Angular Extrusion Pressing
Authors: Alexandrov Igor V. , Budilov I.N. , Krallics György , Kim Hyoung Seop , Yoon Seung Chae , Smolyakov A.A. , Korshunov Alexander , Solovyev V.P.
Published: March 2009

Equal-channel angular (ECA) pressing is the main technique of the severe plastic deformation (SPD) method, applied for fabrication of bulk nanostructured metal materials. At the same time the practical realization of this technique is a rather challenging task. This is connected with the fact that the material during the ECA pressing is subjected to large strains under high imposed pressure at relatively low temperatures.
Simulation with the help of the finite element method (FEM) or the variation-difference (VDM) method is widely applied to analyze the process of ECA pressing. A variety of as commercial as well as in-house developed programs are used by researches, when conducting this analysis. As a result the correlation between the modeling results, obtained at different laboratories as well as their adequacy, i.e. possibilities of their application for the analysis of the experimental data become topical issues.
In order to find answers to the questions put by there has been performed computer simulation of 1st pass of ECA pressing by an example of pure copper at 4 different laboratories, engaged in SPD problems. Meanwhile, the investigators used different software packages, however, initial simulation conditions were set equal. This refers in particular to geometry sizes and the form of the die-set possessing square transverse section of the channels, as well as to the inner and outer curvature radii of the channels in the point where they intersect, and to the form and dimensions of the billet, strain rate, strain curve, isotropic model of the material. The modeling temperature was ambient. The die-set and the punch were assigned as absolutely solid non-deformable bodies. Taking into account the symmetry of the solving task, the modeling was conducted for a half of the billet, cut along the vertical plane, coming through its geometrical center. The friction coefficient was assigned equal to zero, in order to avoid influence of friction on the character of the material flow as well as not to complicate the problem at the given stage of comparison. Other modeling parameters were chosen by each researcher on his own, basing on his experience and conventional approaches to modeling.
Comparison of the obtained modeling results was made by means of matching of the calculated values of the level of the accumulated strain along the bulk of the billet, pressing efforts, and the geometrical form of the billet after ECA pressing. Modeling results were compared with the results of the experimental researches.
Indentation-Induced Deformation Behavior in Martensitic Steel Observed through In Situ Nanoindentation in a Transmission Electron Microscopy
Authors: Ohmura Takahito , Minor A. , Tsuzaki Kaneaki , Morris Jr. John William
Published: March 2009

Deformation behavior in the vicinity of grain boundary in Fe-0.4wt%C tempered martensitic steel were studied through in-situ nanoindentation in a TEM. Two types of boundaries were imaged in the dislocated martensitic structure: a low-angle lath boundary and a high-angle block boundary. In the case of a low-angle grain boundary, the dislocations induced by the indenter piled up against the boundary. As the indenter penetrated further, a critical stress appears to have been reached and a high density of dislocations was suddenly emitted on the far side of the grain boundary into the adjacent grain. In the case of the high-angle grain boundary, the numerous dislocations that were produced by the indentation were simply absorbed into the boundary, with no indication of pile-up or the transmission of strain.
Inhomogeneity of Microstructure and Creep of ECAP Aluminium
Authors: Sklenička Václav , Král Petr , Ilucová L. , Saxl Ivan , Dvořák Jiří , Svoboda Milan
Published: March 2009

High purity (99.99%) pure aluminium processed by equal channel angular pressing (ECAP) was examined in terms of the ECAP microstructure inhomogeneity and its creep behaviour. The results indicate that an inhomogeneity of the ECAP microstructure in mesoscopic scale may influence the creep behaviour of the pressed material.
Deformation Microstructures in a Two-Phase Stainless Steel during Large Strain Deformation
Authors: Tsuzaki Kaneaki , Belyakov Andrey , Kimura Yuuji
Published: March 2009

Deformation microstructures were studied in a two-phase (about 60% ferrite and 40% austenite) Fe – 27%Cr – 9%Ni stainless steel. Severe plastic working was carried out by rolling from 21.3×21.3 mm2 to 7.8×7.8 mm2 square bar followed by swaging from Ø7.0 to 0.6 mm rod at an ambient temperature, providing a total strain of 6.9. After a rapid increase in the hardness at an early deformation, the rate of the strain hardening gradually decreased to almost zero at large strains above 4. In other words, the hardness approached a saturation level, leading to an apparent steadystate deformation behaviour during cold working. The severe deformation resulted in the evolution of highly elongated (sub)grains aligned along the rolling/swaging axis with the final transverse (sub)grain size of about 0.1 μm and the fraction of high-angle (sub)boundaries above 60%. However, the kinetics of microstructure evolution in the two phases was different. In the ferrite phase, the transverse size of deformation (sub)grains gradually decreased during the processing and approached 0.1 μm at strains of about 6.0, while the transverse size of the austenite (sub)grains rapidly reduced to its final value of 0.1 μm after a relatively low strain about 1.0.
Ultra Grain Refinement of Low C Steels by Accumulative Roll Bonding
Authors: Salvatori I.
Published: March 2009

Refinement of grain size is one of the biggest challenges to produce steels with improved combination of strength and toughness. Ultrafine structures are being produced world-wide on various materials, including low carbon steel, using different types of processes. However, the majority of these processes also exhibit severe limitations because they are generally restricted to small samples and are difficult to be implemented on an industrial scale.
A promising technique for industrial implementation is the Accumulative Roll Bonding (ARB), a process able to supply large samples, even in the laboratory scale. In this paper, warm intense straining (ε = 4) by ARB was applied to a plain low-C steel in order to develop ultrafine grains, aiming at sizes around 1-2 μm, suitable to maintain an adequate combination of strength and ductility. The effect of annealing conditions on the evolution of the work-hardened microstructure and the bonding behaviour after each pass were investigated.
Orientation Imaging Microscopy was used to investigate the microstructure and give a quantitative assessment of high angle and low angle boundaries. It is showed that the frequency of high angle grain boundaries increases with the strain but the misorientation distribution remained far from that typical of a recrystallised material.
Scaling up of Equal Channel Angular Pressing (ECAP) for the Production of Forging Stock
Authors: Srinivasan R. , Cherukuri B. , Chaudhury Prabir K.
Published: March 2009

Over the past two decades equal channel angular processing (ECAP) and other severe plastic deformation (SPD) processes have been shown, in the laboratory scale, to produce material with promising properties for industrial applications. In particular, ultrafine grain (UFG) metals produced by ECAP process, for example, have been shown to exhibit higher strain rate sensitivity at lower temperatures and higher strain rates. These factors translate to improved hot formability. However, scale up of these processes to manufacture industrial size components has not been widely undertaken. In this study, billets of annealed AA6061 with 12.5 mm (0.5-in), 50 mm (2-in) and 100 mm (4-in) square cross section were ECAP processed. For the first time, these larger SPD billets were used as starting stock for subsequent hot forging. Several parts were forged on an industrial scale press with the UFG material, as well as conventional stock materials. These parts varied in complexity, as well as size in order to cover the variability in industrial components. This paper will present the effect of scaling up on the mechanical properties, microstructure, and the hot workability of the alloy from the laboratory scale (12.5 mm) to industrial scale (100 mm). Results show that both the forging temperature of the billets and the starting billet size can be substantially decreased compared to conventional forging practice. Therefore, the use of SPD materials, as forging stock, results in decreased energy usage and increased material yield. Results presented will include examples of forged parts, estimated energy savings associated with the use of SPDUFG stock, and properties after forging and subsequent heat treatment.
Specific Features of the Strengthening during Severe Plastic Deformation of Supersaturated Solid Solutions
Authors: Dobatkin Sergey V. , Zakharov Valerij V. , Rokhlin L.L.
Published: March 2009

The effect of the supersaturated solid solution decomposition occurring prior to, during, and after severe plastic deformation by torsion under high hydrostatic pressure on strengthening is examined by the examples of Al-Cu-Mg, Al-Mg-Sc, and Mg-Sm alloys and 0.12%C-0.85%Mn- 0.65%Si and 0,1%C-1.12%Mn-0.08%V-0.07%Ti low-carbon steels. The decomposition of the supersaturated solid solution was realized upon cooling from the quenching temperature (lowcarbon steels), prior to deformation (Al-Cu-Mg-, Mg-Sm alloys), during deformation (Al-Cu-Mg-, Mg-Sm alloys), and after deformation. It is shown, the decomposition of the supersaturated solid solution is effective for the grain refinement down to nanoscale and strengthening, but, for different materials, different combinations with SPD should be used.
Martensitic Transformation and Mechanical Behavior of TiNi Shape Memory Alloys after Severe Plastic Deformation
Authors: Tsuchiya Koichi , Inuzuka M. , Hosokawa Akihide , Tomus Dacian , Nakayama Hiroyuki , Morii K. , Todaka Yoshikazu , Umemoto Minoru
Published: March 2009

Thermal- and stress-induced martensitic transformation was investigated on TiNi shape memory alloys subjected to severe plastic deformation (SPD) by cold rolling. TEM observation revelaed the sample is a mixture of nanocrystalline and amorphous after 40% cold rolling. DSC analysis suggested that the martensitic transformation was suppressed when the thickness reduction was over 25% reduction. Aging at lower temperatures (573 ~ 673 K, 3.6 ks) restores the phase transformations, but to a limited extent. The stress-strain curves of nanocrystalline/amorphous TiNi are characterized by absence of stress-plateau and small hysteresis.
New Routes for Synthesizing Massive Nanocrystalline Materials
Authors: Wilde Gerhard , Boucharat Nancy , Dinda Guru Prasad , Rösner Harald , Valiev Ruslan
Published: March 2009

New opportunities for fabricating massive nanocrystalline materials in bulk quantities are required for facilitating the transition of nanocrystalline solids from laboratory samples to technologically relevant materials. Advanced options might be based on combining different nonequilibrium processing routes sequentially, such that an initially metastable state is continuously energized and successively driven farer away from thermodynamic equilibrium. The current paper presents recent results on the evolution of nanoscaled microstructures resulting from combinations of different plastic deformation treatments or of vitrification and severe plastic deformation.
High Pressure Torsion of Rail Steels
Authors: Wetscher F. , Tian Bao Hui , Stock Richard , Pippan Reinhard
Published: March 2009

To study the influence of shear deformation on the evolution of the microstructure and the mechanical strength in rail steels, three steels with different microstructure (two pearlitic, one bainitic) were deformed by High Pressure Torsion (HPT). In order to evaluate in addition the effect of the strain path, a cyclic form of HPT was applied. The mechanical strength was determined by means of in-situ measurement of the flow stress and microhardness measurements. The differences of the mechanical strengths between the monotonic and cyclic deformed samples clearly indicate that a monotonic deformation promotes higher dislocation densities and leads to the assumption that dissolution of the cementite takes place more pronounced.
Dissolution of Cementite in Carbon Steels by Heavy Deformation and Laser Heat Treatment
Authors: Umemoto Minoru , Todaka Yoshikazu , Ohno Akifumi , Suzuki Mayumi , Tsuchiya Koichi
Published: March 2009

Dissolution behavior of cementite in eutectoid steels with pearlitic and spheroidite structures by severe plastic deformation was studied. Applying a long time milling, cementite dissolved completely and matrix turned out to be nanocrystalline ferrite. By a ball drop deformation (at high strain rates), heavily deformed layers in which cementite dissolves completely or partially were produced. By applying pulsed laser irradiation, re-austenitized zone which transformed to fresh martensite during quenching was produced. The boundary between the re-austenitized zone and matrix exhibited similar microstructure with that observed in specimens subjected to a ball drop deformation. It was suggested that the dissolution of cementite by heavy deformation at high strain rates are probably due to thermal effect, that is, re-austenitization.
On the Microstructure of HPT Processed Cu under Variation of Deformation Parameters
Authors: Schafler Erhard , Dubravina Anna , Mingler Bernhard , Karnthaler Hans Peter , Zehetbauer Michael J.
Published: March 2009

The evolution of strength characteristics and the microstructure of copper subjected to high pressure torsion (HPT) are studied under variation of strain and hydrostatic pressure. Measurements of Multiple X-ray Bragg Profile Analysis (MXPA) yield microstructural parameters like dislocation density and arrangement, as well as crystallite (domain) size and distribution, and long-range internal stresses. TEM investigations are carried out to analyse the structural elements and to compare them with the results of MXPA. The strength behaviour is studied by microhardness measurements. The investigations are performed within wide ranges of resolved shear strains = 1 to 400 and of applied pressures p = 0.8 to 8 GPa. The onset of the deformation stages IV and V is strongly affected by the hydrostatic pressure i.e. shifted to higher values of stress and strain with increasing pressure. The experimental results indicate the occurrence of recovery effects, which seem to be of static as well as of dynamic nature, and to be responsible for extended ductility in SPD materials.
Low Carbon Low Alloy Submicro-Steel with Nano-Precipitation
Authors: Shi Bi , Song Hong Wei , Zhang Jun Bao , Cao Han-Qing , Wang Xiu Fang
Published: March 2009

In the present work, low carbon low alloy submicro-steel sheet has been developed successfully by severe warm-rolling (SWR) at 500 °C through a single pass. The result shows submicro-structure can be fabricated by severe rolling. The formation of the submicro-structure is attributed to the grain refinement mechanism induced by the severe plastic deformation (SPD). The refinement involves the cutting and subdividing of the original micro-crystals into ultrafine grains by dense dislocation arrays. To a certain extent, dynamic recrystallization in ferrite during SWR also seems to contribute to the formation of the submicro-structure. The thermal stability of the submicro-steel was investigated by annealing the steel at different temperatures. The investigation indicated that the submicro-steel can be subjected to annealing at 550°C without apparent grain growth. The unusually high thermal stability can be attributed to the pining effect of numerous uniformly distributed nano-precipitates in the steel. The sizes of the nano-precipitates belong to two different orders. The average diameter of the large precipitates is about 30 nm and the smaller one less than 10 nm.
Strain-Induced Grain Refinement in Magnesium Alloy AZ31 during Hot Forging
Authors: Yang Xu Yue , Xing Jie , Miura Hiromi , Sakai Taku
Published: March 2009

Strain-induced grain refinement in a magnesium alloy AZ31 was studied in multi-directional forging (MDF) at a temperature range from 423K to 623K and at a strain rate of 3x10-3s-1. MDF with a pass strain of 0.8 was carried out to high cumulative strains of around 5 with changing of the loading direction during decreasing temperature from pass to pass. The structural changes can be characterized by the evolution of many mutually crossing kink bands at low strains followed by increase in their number and misorientation, finally resulting in a fully developed fine-grains at high strains. MDF with decreasing temperature can accelerate the evolution of much finer grains and the improvement of plastic workability. An average grain size of 0.3 μm is formed at an accumulative strain of 4.8 and at 423K. It is concluded that grain refinement under MDF conditions occurs by a series of deformation-induced continuous reactions; that is essentially similar to continuous dynamic recrystallization (cDRX).
Microstructure, Texture and Deformation Mechanism of Zr702 Processed by Equal Channel Angular Pressing (ECAP)
Authors: Cao W.Q. , Yu Seng Ho , Hwang Sun Keun , Bacroix Brigitte
Published: March 2009

The commercial purity zirconium (Zr702) has been deformed by Equal Channel Angular Press (ECAP) up to eight passes using route A and BC. The deformation microstructure and the bulk texture have been characterized by Electron Backscattered Diffraction (EBSD) in SEM and X-rays diffraction (XRD), respectively. The homogeneously lamellar deformation structure in route A and the equiaxed deformation structure with local heterogeneity in route BC have both been determined. In both cases the subgrain size flattened at about 0.33 ìm after 2 passes but average misorientation increased with increasing strain. After 8 passes high angle fraction is over 70% both in route A and route BC. The bimodal {0002} pole texture (high strain rolling texture) in route A and the strong unimodal {0002} pole texture with weak high strain rolling texture in route BC have been identified. The boundary texture has been analysed both in sample frame and crystallographic frame. It was found in sample frame that the boundary texture of high angle boundaries developed gradually in route A and more strongly than that in route BC, implying that the boundary characters evolved from the mixed characters (tilted and twist) to tilted boundary in route A. Based on the deformation structures and the bulk textures, the deformation mechanism of large local orientation rotation and the stability of the dislocation structures have been proposed to interpret the grain refinement and the texture development of Zr702 during ECAE processing.