bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow Curve Modelling of an Austenitic Stainless Steel at High Temperatures Starting from the One-Parameter Model of Strain Hardening
Authors: Angella Giuliano
Published: January 2012

The flow curves of an austenitic stainless steel deformed at temperatures 700-1000°C with strain rates 10-5-10-2 s-1 were modelled with the Voce equation. The parameters needed to draw the Voce equation, are the saturation stress σV that defines the height of the flow curve, the critical strain εC that defines the velocity to achieve σV, and the stress σo, namely the back-extrapolated flow stress to zero strain. A modified strain hardening analysis based on the one-parameter model was used to analyze the strain hardening rate dσ/dε vs. the flow stress σ in order to obtain σV and εC. The modified approach was based on the assumption that the dislocation multiplication component of strain hardening was temperature and strain rate dependent through the thermal activation term s of flow stress. A parameter s’ proportional to s was obtained from the strain hardening analysis and a relationship between s’ and temperature and strain rate was found. Relationships between σV, σo, εC and s’ were finally established and at this stage the Voce equation could reproduce the experimental flow curves at any imposed deformation conditions of temperature and strain rate.
Interface Motion and Interface Mobility of the Partitioning Phase Transformations in Fe-Mn-C and Fe-C Alloys: A Cyclic Phase Transformation Approach
Authors: Chen Hao , Appolaire Benoît , van der Zwaag Sybrand
Published: January 2012

A cyclic phase transformation concept has been proposed to investigate the growthkinetics of the austenite (γ) to ferrite (α ) and vice versa in Fe-Mn-C and Fe-C alloys. In the caseof cyclic partial transformations in Fe-Mn-C alloys, two new and special stages are observed:a stagnant stage in which the degree of transformation does not vary while the temperaturechanges and an inverse phase transformation stage, during which the phase transformationproceeds in a direction contradictory to the temperature change. The local equilibrium (LE)and paraequilibrium (PE) are both applied to analyzing the new observations. The stagnantstage was found to be caused by the Mn partitioning, while the inverse phase transformationstage was due to equilibrium conditions not being reached at the transition temperatures.A mixed-mode model is applied to simulating the cyclic phase transformation in Fe-C alloy,and it is found that the cyclic phase transformation concept is a very promising method forinvestigating the interface mobility.
Hydrogen Charging of High Strength Steel Specimens and Physical Simulation of Cold Cracking under Laser Beam Welding Conditions
Authors: Dreibati Ossama , Ossenbrink R. , Michailov Vesselin
Published: January 2012

Cold cracks occur during the cooling down of welded joint at low temperatures or later at room temperature after the end of welding. It is associated with the formation of brittle microstructures as martensite in the presence of diffusible hydrogen as well as of tension stresses. By using an enhanced Simulation-und Testing Center Gleeble 3500, a procedure for physical simulation of cold cracking under laser beam welding conditions is suggested. The approach reproduces combinations of the cold crack main parameters, a brittle microstructure, tension stress and high local hydrogen concentration under welding conditions which induce a cold crack. A specimen geometry and technique were developed to enable the gaseous hydrogen charging from pure hydrogen atmosphere. The amount of charged hydrogen can be adjusted through varying the charging parameters like temperature, gas pressure and charging time. The hydrogen charging technique and the cold crack testing procedure were proven with high strength steel specimens.
Study of Transverse Crack Formation of a Nb-Peritectic Steel
Authors: Nafisi S. , Collins L. , Szekeres E.S.
Published: January 2012

The problem of transverse crack formation in continuously cast steel has been an issue for over 30 years. The crack susceptibility depends not only to the steel composition, but also to the temperature history during casting. To improve the surface quality, two key solutions have been suggested; adjusting the straightening stage to an appropriate temperature range, out of hot ductility trough, and/or alloy modification. These solutions have certain limitations and difficulties still exist for grades such as peritectic steels containing Nb or V. In this article, the hot ductility of a peritectic steel grade with Nb has been studied under direct cast conditions. This was performed using a Gleeble 3800 thermo-mechanical simulator under two critical strain rates. In addition, the transverse crack formation and appearance, as well as the application of infrared camera to study the surface temperature profile of the slabs is presented.
Characterization of WELD Heat Affected Zone of ASTM A709 HPS 100W
Authors: Biswas Avidipto , Nash Philip , Lalam Sreeharsha , Jansto Steve
Published: January 2012

The weld heat affected zone (HAZ) of HPS 100W was characterized in terms of microstructure and mechanical properties. HAZ simulation was carried out in a GLEEBLE 3500 along with in-situ dilation tests at different peak temperatures of 850°C, 1100°C, 1300°C and 1350°C with heat input of 2kJ/mm. Subsequently, impact toughness data were obtained at different temperatures by means of Charpy tests. The microstructures were characterized using optical microscope, SEM and TEM to correlate the structure-property relationship of the HAZ. Under the tested conditions, all the simulated HAZs exhibited higher impact toughness than the base metal.
Physical and Numerical Simulation of Thermo-Mechanical Properties in the Weld Heat Affected Zone of an AlMgSi-Alloy
Authors: Dreibati Ossama , Ossenbrink R. , Doynov Nikolay , Michailov Vesselin
Published: January 2012

The thermomechanical properties of an AlMg0,8Si1 (corresponds to EN AW-6181) alloy in T4 state (Ecodal® 608) were investigated under coldArc® welding conditions using Gleeble 3500 concerning the numerical simulations of residual welding stresses and distortions. Thereby, tensile tests were carried out during the heating phase, cooling phase and after natural aging up to 10 days. Thus, the effect of weld cycle and corresponding dissolution of β''(Mg2Si)- precipitates on the mechanical properties was physically simulated. Furthermore, two phase transformation models were used to simulate the dissolution of hardening precipitates as a result of weld temperature cycles. The used models were compared, considering their capabilities and accuracy.
Modelling the Flow Behaviour of Dual-Phase Steels with Different Martensite Volume Fractions by Finite Element Method
Authors: Marvi-Mashhadi M. , Rezaee-Bazzaz A. , Mazinani Mohammad
Published: January 2012

Dual-phase (DP) steels have a composite-type microstructure consisting mainly of hard martensite islands embedded in a soft ferrite matrix. DP steels exhibit a characteristic combination of high strength, high work hardening rate and good ductility. Mechanical behaviour of DP steels is closely related to their microstructures. Hence, it is necessary to take into account their microstructural parameters in any attempt to estimate their flow behaviour. In this study, the flow curves of low carbon DP steels with 26.4 and 52% martensite produced by intercritical annealing processes at different temperatures were calculated using the finite element method (FEM). According to the results of microscopical observations of steel microstructures, martensite islands were assumed in the model to be spherical in shape. Moreover, in agreement with the experimental results in the literature clearly showing the possibility of martensite plastic deformation in similar steels during straining when its volume fraction is greater than about 30%, the plasticity of martensite islands in the steel microstructures was taken into account in the model by using their experimentally obtained stress-strain relations as a function of their estimated carbon contents. Having estimated the stress-strain behaviour of the ferrite phase in all steel samples using the microstructural parameters corresponding to the starting ferrite+pearlite steel, the flow curves of different DP steel samples with elastic martensite (in low martensite content steels) and elasto-plastic martensite (in high martensite content samples) were calculated. The calculated stress-strain curves exhibited reasonable agreements with the experimental stress-strain curves obtained from the tensile tests.
Computer Simulation of Spinodal Decomposition in Duplex Stainless Steels
Authors: Saito Yoshiyuki
Published: January 2012

Numerical simulations of phase separation in Fe-Cr-Mo―Ni or Fe-Cr-MoーTi quaternary alloys similar to ferrite phases in dplex stainless steeswere performed by the Cahn-Hilliard equation. We obtained that the asymptotic behaviour of minor element Ni, Mo, Ti in an Fe-Cr-X quaternary alloy along a trajectory of a peak top of the major element Cr is classified into three groups according to the sign of the second derivative of the chemical free energy with respect to the compositions of Cr and X(X=Mo, Ni or Ti]. It is also predicted that that small addition of Mo upto 10% accelerates phase separation of Cr. It seems that the optimum value of Mo exists to enhance the phase separation of Cr in Fe-Cr-Mo ternary alloys. Simulation result indicates that the phase separation of Cr is most enhanced with addition of 1% Mo. The above mentioned simulation results given by the numerical simulation by the Cahn-Hilliard equation were in good agreement with those obtained by the Monte Carlo simulation Theoretical analyses were performed in order to discuss the simulation results. On the basis of theb simulation results Optimum materials design of the duplex stainless steel has been established.
The Influence of the Impeller Shape on Hydrogen Removal from Liquid Aluminium - Physical Model
Authors: Saternus Mariola
Published: January 2012

Today the barbotage process is commonly used for refining aluminium and its alloys. There are many refining reactors available all over the world. The refining gas can be introduced to the liquid metal by nozzles, ceramic porous plugs and rotary impellers. The last ones become the most popular. The shape of impellers is different and influences the level of gas dispersion in the liquid metal. Physical modelling is quite often used for modelling the aluminium barbotage process. In this way it is possible to observe the phenomena that take place in the whole process. Results obtained from this kind of research can be representative and transformed to real conditions if the test stand is built according to the theory of similarity. The test stand was built for modelling the refining process in the URO-200 reactor. Three different shapes of impellers were tested. The processing parameters like the flow rate of refining gas and the impeller rotary speed changed in the range from 5 to 15 dm3/min and from 0 to 500 rpm respectively. Additionally the research of oxygen removal from water was carried out as an analogy of hydrogen removal from liquid aluminium. The level of oxygen was measured by means of oxygen meter Elmetron CO-401. The obtained results were discussed and graphically presented.
Modeling Particle Distances of Coherent Prolate- and Oblate-Shaped Precipitates in bcc Systems
Authors: Sonderegger Bernhard , Kozeschnik Ernst , Sommitsch Christof
Published: January 2012

In a wide range of materials, precipitation hardening is the key for optimizing properties such as strength or creep performance. In order to model strengthening effects with physically based concepts, precipitate kinetic simulations have to be linked to micromechanical models. Part of this link is the precipitate distance distribution in the glide planes of dislocations. Recently, a new model for the calculation of distance distributions has been introduced, which is specially designed for arbitrary size distributions and, thus, capable of handling more realistic microstructures when compared to classical approaches. Up to now, this model has been restricted to spherical precipitates. In this work, the model is advanced to account for all kinds of spheroids, that is, ellipsoids with rotational symmetry. Any prolate, oblate or globular precipitate shape can be represented by a specific shape factor, or aspect ratio, and an effective radius. The result is represented in the form of a multiplicative factor for particle distances depending on the aspect ratio only, and can be expressed as a single explicit formula. It is shown, that prolate shape is most effective for minimizing particle distances in glide planes, followed by oblate shape and finally spheres. Since numerous precipitate types feature needle-or platelike shapes, the present model offers a wide field of applications.
Evaluation of the Effects of Inclusion Distribution on the Local Ductility of DP Steel
Authors: Suwa Y. , Matsuno T. , Hirose S. , Fujita N. , Seto A.
Published: January 2012

In the present study, the effects of inclusions on the local ductility of DP steel are investigated using finite element analysis (FEA). In order to evaluate local ductility, a continuum damage mechanics (CDM) model has been incorporated into the Abaqus/Explicit® commercial finite element code. Furthermore, three-dimensional representative volume elements (RVEs) with ferrite, martensite, and inclusion phases have been used to evaluate the stress-strain response. Simulation results show that the volume fraction of the martensite as well as the difference in hardness between the ferrite and the martensite phases dominates the effect of inclusions on local ductility.
Ferrite Transformation Kinetics of Severely Hot-Deformed Austenite
Authors: Yanagida Akira , Liu J. Jin Shan , Yanagimoto Jun
Published: January 2012

The ferrite transformation kinetics of severely hot-deformed austenite has been studiedby considering ferrite nucleation from dislocation cell blocks inside austenite grains. The size ofdislocation cell blocks and ferrite grain size just after phase transformation are acknowledged to beinversely proportional to the square root of dislocation density. It is found that the ferrite nucleationrate in this area can reach the saturated state at a high temperature just under Ae3, and the ferritetransformation finishes within a very short time. The kinetics of ferrite volume fraction and theferrite grain growth after phase transformation for plain carbon (0.1%C, 0.2%Si, 1.0%Mn) steelhave been studied using a THERMECMASTER hot-compression testing machine. These modelscan be applied to the hot and warm forming processes of plain carbon steel to predict the ferritetransformation from severely deformed austenite.
Effect of Grain Size on the Hydrogen Diffusion Process in Steel Using Cellular Automaton Approach
Authors: Yazdipour N. , Dunne D.P. , Pereloma Elena V.
Published: January 2012

The role of microstructure in susceptibility to hydrogen uptake and property degradation is being evaluated using a number of high strength pipeline steels. To do so, a cellular automaton (CA) model has been used to examine the effect of grain size, as a first step in assessing the influence of microstructure. The simulation results of hydrogen diffusion into microstructures with different grain sizes are presented.
Simulation and Control of Distortion of Hydro Turbine Blade Steel Casting in Heat Treatment Process
Authors: Yu Hai Liang , Kang Jin Wu , Huang Tian You
Published: January 2012

Blades are key part of hydro turbines, which often distorts during heat treatment process for their special structures. In this paper, thermal fluid finite element simulation of the forced air cooling process of a blade casting was carried out under a variety of distances between fans and blades, air speeds, groups of fans and circumstance temperatures. The temperature fields of blade castings were obtained. A novel parameter, temperature difference between surfaces of castings along thickness direction, was proposed to analyze the distortion of blade castings. The distortion behavior of blade castings with martensitic stainless steel were discussed, which is in good agreement with distortion regularity of the experimental ones. The temperature differences between blade casting surfaces are always greater than zero, resulting in distortion which could be divided into three stages. Finally, we focused on discussing the control methods of distortion behavior of blade castings which could be operated in actual production.
Numerical Simulation of Dynamic Strain-Induced Austenite-Ferrite Transformation and Post-Dynamic Kinetics in a Low Carbon Steel
Authors: Zheng Cheng Wu , Raabe Dierk , Li Dian Zhong
Published: January 2012

2-D cellular automaton model was developed to simulate the dynamic strain-induced transformation (DSIT) from austenite (γ) to ferrite (α) and the post-dynamic kinetic behavior in a low carbon steel with the purpose of developing a methodology of mesoscopic computer simulation for an improved understanding of the formation of ultra-fine ferrite (UFF) in DSIT and the conservation of this microstructure during the post-deformation period. The predicted microstructure obtained after DSIT was compared with a quenched dual-phase steel. Its microstructure, consisting of fine-grained ferrite and fine islands of retained austenite dispersed in the matrix, were found to be in good agreement with the predictions. The simulated results indicate that the refinement of ferrite grains produced via DSIT can be interpreted in terms of unsaturated nucleation and limited growth mechanisms. It is also revealed that continuing transformation from retained austenite to ferrite and the reverse transformation both could take place simultaneously during the post-deformation isothermal holding. A competition between them exists at the early stage of the post-dynamic transformation.
Size Effects and Structure-Sensitivity of Properties in Electrodeposited Nanomaterials
Authors: Erb Uwe
Published: January 2012

An analysis of grain-size dependent structure-sensitivity of various physical and mechanical properties of nickel is presented, covering the crystal size range from 10 nm to 10 μm. It is shown that the well established general trends regarding defect-sensitivity observed for conventional polycrystalline materials also apply to porosity-free nanomaterials with grain sizes less than 100 nm produced by the electrodeposition process.
Shape Memory Epoxy Foams: New Materials for Aerospace Applications
Authors: Santo Loredana
Published: January 2012

In this paper, shape memory epoxy foams, obtained by the new solid-state foaming process for thermosetting resin powder, are investigated. Foaming experiments in different configurations, compression tests, constrained stress recovery tests, and density measurements are discussed. The interesting results seem to be very promising for the aerospace application of shape memory epoxy foams as light actuators, structural parts with reduced size during shipping, and expandable/deployable structures. Finally, an attractive experiment is introduced. It is designed for the next Space Shuttle STS-134/ULF-6 in I-25/26, on April 2011, with the aim to study the behavior of this new class of materials in microgravity.
Residual Strain Distribution around a Fatigue-Crack Tip Determined by Neutron Diffraction
Authors: Huang E Wen , Li Kuan Wei , Lee Soo Yeol , Woo Wanchuck , Ding Yi Shiun , Tsay Leu Wen , Chen Chung Hao
Published: January 2012

An analysis of residual stress, one of the contributory factors to the crack tip driving force, is extremely important to probe the fatigue crack growth mechanism and to further develop the life prediction methodology. Since fatigue crack growth is governed by crack-tip plasticity and crack closure in the wake of the crack tip, the investigation of residual stain/stress field in both behind and in front of the crack tip is crucial. In the current work, a 304L stainless steel compact-tension specimen is pre-cracked under constant-amplitude cyclic loading. Neutron diffraction is employed to directly measure the three orthogonal residual strain fields with 1-mm spatial resolution as a function of distance from the crack tip. The mapping results show that the three orthogonal residual-strain distributions around the crack tip depend on the stress multiaxiality, not following a single Poisson relationship to each axis.
Structure of Disordered Materials Studied by High-Energy X-Ray Diffraction Technique
Authors: Kohara Shinji , Ohara Koji , Temleitner L. , Ohishi Y. , Fujiwara A. , Takata Masaki
Published: January 2012

With the arrival of the third generation of synchrotron sources and/or the introduction of advanced insertion devices (wigglers and undulators), the high energy (E > 50 keV) x-ray diffraction technique has become feasible, leading to new approaches in the quantitative study of the structure of disordered materials than was hither to available. Since we built the SPring-8 bending magnet beamline BL04B2 and two-axis diffractometer for disordered materials in 1999, we have studied on disordered materials from ambient to extreme condition. In this article, the high-energy x-ray diffraction beamline BL04B2 of SPring-8 and recent developments of ancillary equipment (automatic sample changer, conventional high-temperature furnace, aerodynamic levitation furnace) are introduced. Furthermore the structural analysis on the basis of diffraction data with the aid of computer simulations, which we performed in the last 10 years is reviewed.
Bainite Formation at Low Temperatures in High C-Si Steel and its Mechanical Behavior
Authors: da Cruz José Alberto , Rodrigues Thiara Francis Mateus , Viana Virgínia Dutra Costa , Santos Dagoberto Brandão
Published: January 2012

A significant amout of stabilized austenite can be obtained in high carbon steel containing high amounts of manganese and silicon (1.5-2 %). At relatively low temperatures the bainite plates formed are extremely thin, making the material very strong. In this study, the influence of the thermal cycle of austempering on the mechanical behavior of a spring steel 0.56C-1.43Si-0.58Mn-0.47Cr (wt. %), with TRIP effect was investigated. The thermal cycle consisted of heating three groups of hot-rolled wire steel at austenite field of 900°C for 300 s, and quickly transferring those to a metallic bath maintained at 200, 220 or 270°C, respectively, for different heat treatment times. The samples were then tested in tension and their microstructures were examined by scanning and transmission electron microscopy. The samples treated at 220°C showed higher elongation, yield strength and tensile strength than those maintained at 200 or 270°C. The high level of strength and ductility is due to a mixture of martensite and very fine bainitic ferrite with interlath film of retained austenite. The temperature has shown a strong influence on bainite formation kinetics. The fracture behavior of the steel was also evaluated using SEM fractography.
Local Residual Stress Distribution at the Tooth Root Surface of a Broached Steel Component
Authors: Strauss Tobias , Meier Harald , Gibmeier Jens , Schulze Volker , Wanner Alexander
Published: January 2012

Broaching is an important technique for creating tooth structures in mechanical components. In the present work, the effects of the broaching process on the material state in the near surface region at the root of the tooth was analyzed. The studies were carried out on broached plates made from case hardening steel SAE 5120. The cutting speed and machining condition (cooling lubricant, dry machining) were varied. During broaching with a TiAlN coated tool the cutting forces were monitored. Subsequently, the local residual stresses at the root of the tooth were determined using X-ray diffraction. Further, surface roughness and micro hardness measurements as well as microstructure analysis complement the results. The results indicate that cutting forces have a high influence on the development of the residual stress state at the machined surface whereas no significant effect on changes in surface hardness and microstructure could be observed. Dry cutting with relatively high cutting speeds (≥ 30m/min) result in low cutting forces and hence in high tensile residual stresses in broaching direction.
Numerical Analysis in the Process of Alternate Pressing and Multiaxial Compression
Authors: Kwapisz Marcin , Knapiński Marcin , Dyja Henryk , Laber Konrad Błażej
Published: January 2012

This article presents the results of numeric simulation obtained with commercial software for thermo-mechanical analysis of plastic forging processes, Forge 2009, of the process of alternate forced pressing and multiaxial compression. The new method of alternate forced pressing and multiaxial compression suggested by the authors is characterized by the presence in the plastically forged material of the similar states of deformations to those present in the processes of the equal channel angular pressing and cyclic extrusion compressing. From the performed preliminary tests it can be stated that as a result of combining and repeating two alternate operations: pressing and multiaxial compression, strain accumulation and development of deformation state favorable to grain crushing take place.
Shear Strength Measurement of Gum Metal during High-Pressure Torsion
Authors: Furuta Tadahiko , Kuramoto Shigeru , Nagasako Naoyuki , Horita Z.
Published: January 2012

In the present study, in situ measurements of applied torque and compressive load were conducted during high-pressure torsion (HPT) on Ti-23%Nb-0.7%Ta-2.0%Zr-1.2%O (in at %) , Gum Metal, by using four active strain-gage method. The shear stress was then calculated from the measured torque. The in situ measurements revealed that the maximum shear stress reaches ~2 GPa during HPT. This value is comparable to the ideal shear strength of Gum Metal, which was reported as ~1.8 GPa from experiments using single crystals. The deformation mechanism strongly depends on body-centered cubic (bcc) phase stability at an early stage of HPT straining, where the shear stress is well below the ideal shear strength. On the other hand, the deformation mechanism may be insensitive to the bcc phase stability at a later stage of HPT straining, where plastic deformation occurs at a strength close to the ideal shear strength.
Grain Refinement of Magnesium Alloys by CONFORM: A Continuous Severe Plastic Deformation Route?
Authors: He You Liang , Gao Fei , Song Bao Yun , Fu Rong , Wu Gui Ming , Li Jian , Jiang Lan
Published: January 2012

Effective grain refinement through equal channel angular pressing (ECAP) for magnesium (Mg) alloys has been demonstrated by many researchers. Although with the capability to achieve superplasticity, the batch mode nature of this method and the required repetitive processing to attain ultrafine grained structure have prohibited it from being widely used in large-scale industrial production. In this study, a well-established metal forming method – the continuous extrusion forming (CONFORM) process – was employed as a severe plastic deformation route to refine the microstructure of Mg alloys. Cast Mg-3%Al-1%Zn (AZ31) rods were used as the feedstock and the cast structure (grain size of ~150 microns) was refined to ~1 micron after one pass CONFORM extrusion. Uniaxial tensile tests of the as-extruded samples were conducted at a temperature of 473K and an elongation of ~200% was achieved under a strain rate of 1×10-4 s-1. The significant grain refinement effect was attributed to the severe shear deformation occurred during the CONFORM process, which is very similar to ECAP but with even higher effective strains. The most important advantage of CONFORM over ECAP is that the former is a continuous route, so it is able to produce long products. It was also shown that CONFORM could be an additional forming method for Mg alloys to conventional rolling, forging and extrusion.
Ultrafine Grain Formation in Aluminum Alloys during Hot Severe Plastic Deformation
Authors: Sakai Taku , Miura Hiromi
Published: January 2012

The evolution process of ultrafine grains during hot severe plastic deformation (SPD) was studied in several aluminum alloys. The structural changes can be characterized by the evolution of deformation bands such as microshear bands (MSBs) at moderate strains. The process of strain-induced grain formation can be categorized into the three stages irrespective of deformation mode and temperature: i.e. i) an incubation period for new grain evolution in low strain; ii) a grain fragmentation by frequent development of MSBs and subsequently new grains in medium strain, and iii) a full development of fine grains in large strain. Temperature effect on the new grain formation in aluminum alloys is also analysed in detail and the mechanism operating is discussed.
Effect of Grain Boundaries on Fracture Toughness in Ultraﬁne-Grained Metals by Atomic-Scale Computational Experiments
Authors: Shimokawa Tomotsugu , Tanaka Masaki , Higashida Kenji
Published: January 2012

In order to investigate roles of grain boundaries on the improved fracture tough-ness in ultraﬁne-grained metals, interactions between crack tips, dislocations, and disclinationdipoles at grain boundaries are performed to aluminium bicrystal models containing a crackand h112i tilt grain boundaries using molecular dynamics simulations. A proposed mechanismto express the improved fracture toughness in ultraﬁne-grained metals is the disclination shield-ing eﬀect on the crack tip mechanical ﬁeld. The disclination shielding can be activated whena transition of dislocation sources from crack tips to grain boundaries and a transition of thegrain boundary structure into a neighbouring energetically stable boundary by emitting dis-locations from the grain boundary occur. The disclination shielding eﬀect becomes large asdislocations are continuously emitted from the grain boundary without dislocation emissionsfrom crack tips. This mechanism can further shield the mechanical ﬁeld around the crack tipand obtain the plastic deformation by dislocation emissions from grain boundaries, hence itcan be expected that the disclination shielding eﬀect can improve the fracture toughness inultraﬁne-grained metals
Specific Mechanical Properties of Superplastically Formed Components and Resulting Applications for Vehicles
Authors: Vorobyov Kyrylo , Danchenko Valentyn , Beeh Elmar , Kopp Gundolf
Published: January 2012

The technical requirements to produce parts as light as possible with more complex geometries are ever increasing in recent years in automotive industries, rail vehicle and aerospace. Manufacturing technologies such as super-plastic metal forming, which had been considered as a niche technology earlier, is now gaining greater technical relevance for industrial size production. The parts that have been generated through super-plastic forming in innovative vehicle for example Mercedes SLS AMG reflect the industrial activity in this area. Manufacturability of thin-walled structures enables lightweight design. Also the tool and manufacturing costs are lower in comparison. However, the main challenge could be found in maintaining exact process parameters. There is a large research potential in super-plastic forming; from the determination of optimal material data through process simulation to manufacturing of real parts and their characterization. In the framework of the project international Bureau of the Federal Ministry of Education and Research UKR005/08 “Manufacture of parts with special properties” a preliminary research work has been carried out.
Deformation Texture of Ti-26mol%Nb-3mol%Al β-Titanium Alloy
Authors: Inamura Tomonari , Shimizu Ryutaro , Hosoda Hideki , Miyazaki Shuichi
Published: January 2012

The effect of reduction rate on the deformation texture of cold-rolled Ti-26mol%Nb-3mol%Al shape memory alloy was investigated. The alloy is the parent phase (β: bcc) at room temperature (RT) and the martensite start temperature is much lower than RT; no residual martensite was detected after cold-rolling. The reduction rate, r, was varied in the range of 60 ~ 99%. Texture evolution was as following; γ-fiber à {001}<110> à {001}<110> + {112}<110> (α-fiber). The strength of {001}<110> was maximized at about r = 97%. The recrystallization texture is expected to be controlled by the reduction rate; optimization of r is supposed to be promising to obtain the {001}<110> recrystallization texture that is preferred for superelastic deformation.
Thermoelectric Properties and Densification Behavior of SrTiO3/TiB2 Composites
Authors: Ito Mikio , Hasegawa Naoki
Published: January 2012

The establishment of rapid synthesis process at a low temperature of thermoelectric non-doped and Y-doped SrTiO3 was tried by using the polymerized complex process and the pulsed current heating method with addition of TiB2 powder. The TiB2 addition was quite effective for reduction in the electrical resistivity of the thermoelectric SrTiO3, and the power factor of the Sr0.9Y0.1TiO3/TiB2 composite was similar to that of the Sr0.9Y0.1TiO3 polycrystal synthesized by the conventional solid state reaction method. It was also found that the addition of TiB2 significantly reduced densification temperature during sintering. This rapid consolidation caused by TiB2 addition was available even when the composite powder was sintered by conventional hot pressing.
Stability of Ti-Ta Base High Temperature Shape Memory Alloys
Authors: Kim Hee Young , Kanaya Takafumi , Fukushima Tatsuhito , Bueconsejo Pio John S. , Miyazaki Shuichi
Published: January 2012

The stability of shape memory properties was investigated by thermal cycling tests in Ti-23Ta-(2-4)Sn alloys. The martensitic transformation temperature decreased considerably after aging at 573 K for the Ti-23Ta-2Sn alloy. The decrease in the martensitic transformation temperature by the aging effect was suppressed by the addition of 3at.%Sn and more to the Ti-23Ta alloy. The Ti-23Ta-3Sn alloy exhibited better cyclic stability compared with a Ti-32Ta alloy which has a similar transformation temperature.
Smart Processing of Micro Photonic Crystals for Terahertz Wave Control - Freeform Fabrication by Stereolithographic Technique -
Authors: Kirihara Soshu , Ohta Noritoshi , Takinami Youhei , Tasakai Satoko
Published: January 2012

Photonic crystals with periodically arranged structures of ceramics can reflect light or electromagnetic waves through Bragg diffraction and exhibit forbidden gaps in transmission spectra. We have successfully fabricated micro diamond crystals including twined lattices with plane defects to realize wavelength selections in terahertz frequency ranges. Novel smart processing composed of computer aided design, manufacturing and evaluation was established. The terahertz waves are expected to detect micro cracks in material surfaces and structural defects in electric circuits by fine wave interferences, and to analyze cancer cells in human skins and toxic bacteria in natural foods through high frequency excitations. In the fabrication processes using micro patterning stereo-lithography, the photo sensitive resin paste including alumina fine particles were spread on a glass substrate with 10 µm in layer thickness by moving a knife edge, and cross sectional images of ultra violet ray were exposed by using a digital micro mirror device with 2 µm in part accuracy. Through the layer stacking process, micrometer order structures were formed exactly. Dense ceramic components could be obtained through dewaxing and sintering heat treatments. The electromagnetic wave transmission spectra were measured by terahertz wave spectroscopy. The micro diamond lattices could form perfect photonic band gaps opining for all crystal directions. The introduced plane defects realized the wave select resonations. This resonation behavior was visualized and analyzed by finite difference time domain simulations.
Study on Binder System for Micro Powder Injection Molding of ZrO2 Ceramic
Authors: Liu Lin , Ni X.L. , Yin Hai Qing , Qu Xuan Hui
Published: January 2012

Micro powder injection molding has been accepted as a potential forming technology for large-scale production of miniature components in industries. However, mold filling capability is often poor due to the blind hole structure of the die cavity, which restricts the widespread application of this technique. In this paper, ZrO2 micro gears with addendum circle ranging from 900μm to 200μm were studied. Instead of using traditional PW-HDPE-SA binder as in powder injection molding, thermoplastic binder system is optimized here for better replication of micro gear. It is found that the dimensional accuracy and demold after injection molding can be improved by utilizing proper binder system. ZrO2 feedstock with a powder loading of 46vol.% and the binder system consisting of BW, HDPE and SA was successfully injection molded and demolded, which indicates good mold filling capability and sufficient demolding strength. The binder system was successfully removed by debinding process in two steps, solvent debinding followed by thermal debinding. Debound components free of defects were obtained. Keywords: Micro powder injection molding, ZrO2 feedstock, Binder system, Molding filling capability, Demolding strength
Multi-Functional Metal/Ceramic Hybrid Composites for Structural Applications
Authors: Nanko Makoto , Maruoka Daisuke , Thuy Nguyen Dang
Published: January 2012

Some ceramic based hybrid composites with metallic particles have excellent mechanical properties. In particular, metal/ceramic nanocomposites has high mechanical strength and improved fracture toughness. Magnetized hybrid composites can be produced by dispersing Fe, Co or Ni nanoparticle in the structural ceramics. Crack healing of metal/ceramic hybrid composites was investigated for structural applications. Cracks of nanoNi/Al2O3 introduced by the Vickers indentation of 49 N could be repaired completely, for example, by air oxidation at 1200°C for 6 h. Even larger cracks introduced by 490 N indentation was healed up to a comparable level of mechanical strength by oxidation at 1200°C for 24 h in air. Outward diffusion of cations during high-temperature oxidation would cause crack repair by filling with an oxidation product. Faster crack disappearance, 900°C for 1 h, was realized on Mo/Al2O3. Surface crack healing effectiveness promoted by outward diffusion of cations is potentially applied into various Al2O3 based hybrid material systems, as well as excellent mechanical properties.
Training Effects on Damping Capacity in Mn-22.5mass%Cu-5mass%Ni-2mass%Fe Alloy
Authors: Watanabe Yoshimi , Suga Yuusuke , Miura-Fujiwara Eri , Sato Hisashi , Nishino Yoichi
Published: January 2012

The training treatments in the shape memory alloy are known as useful method to improve the shape memory effect. In our previous study, it was shown that the training treatments can also improve both the damping capacity and the hardness of the Fe–Mn alloy. In this study, training effects on damping capacity in solution treated Mn-22.5mass%Cu-5.08mass%Ni-1.96mass%Fe alloy have been investigated. As training treatments, the thermal training (only thermal cycling) and the thermo-mechanical training (thermal cycling with deformation) are carried out. Internal friction was measured at room temperature (R. T.) using a free-decay method. Although training effect cannot be found for the samples trained at higher annealing temperature (600 °C and 700 °C), damping capacity of the alloy is improved by thermal training annealed at 400 °C and 500 °C. The trade-off between the damping capacity and mechanical properties can be overcome by the training at lower temperature.
Hot-Rolling of Advanced High-Manganese C-Mn-Si-Al Steels
Authors: Dobrzański Leszek Adam , Borek Wojciech
Published: January 2012

The high-manganese austenitic steels are an answer for new demands of automotive industry concerning the safety of passengers by the use of materials absorbing high values of energy during collisions. The chemical compositions of two high-manganese austenitic steels containing various Al and Si concentrations were developed. Additionally, the steels were microalloyed by Nb and Ti in order to control the grain growth under hot-working conditions. The influence of hot-working conditions on a recrystallization behaviour was investigated. Flow stresses during the multistage compression test were measured using the Gleeble 3800 thermo-mechanical simulator. To describe the hot-working behaviour, the steel was compressed to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). The microstructure evolution in successive stages of deformation was determined in metallographic investigations using light microscopy. The flow stresses are much higher in comparison with austenitic Cr-Ni and Cr-Mn steels and slightly higher compared to Fe-(15-25) Mn alloys. Making use of dynamic and metadynamic recrystallization, it is possible to refine the microstructure and to decrease the flow stress during the last deformation at 850°C. Applying the true strains of 0.23 and 0.19 requires the microstructure refinement by static recrystallization. The obtained microstructure – hot-working relationships can be useful in the determination of powerful parameters of hot-rolling and to design a rolling schedule for high-manganese steel sheets with fine-grained austenitic structures.
Effect of Varying High Frequency Induction Bending on the Longitudinal SAW Weld of API X80 Steel Pipe
Authors: Silva R.A. , Batista G.Z. , de Souza L. Felipe G. , Bott Ivani de Souza
Published: January 2012

Hot induction bending is a process applied to tubes produced for the oil and gas industry, where bending temperatures above Ac3 can be reached. The base metal is submitted to two thermal cycles, one during welding, generating the heat affected zone (HAZ), and another during bending when this HAZ is reheated. Also, after the bending process is completed, heat treatment is required, which represents a third thermal cycle. The objective of the present work was to compare the effect of two different induction bending process conditions on the longitudinal SAW weld of two API 5L X80 steel pipes of 20” diameter, 19mm thickness, Pcm of 0.17% and Σ NbTiV of 0.11%. The pipes, were produced by the UOE process from a steel plate obtained by thermomechanical processing without accelerating cooling. The bending parameters applied were 105 kW power at 2500 Hz frequency and 205 kW at 500Hz A major microstructural decomposition of the welded joint occurred for the 205 kW / 500Hz condition due to the higher heat input in function of the doubled power input during bending. These microstructural changes led to an inversion of the microhardness profile from the internal pass to the external pass as compared to the welded joint before bending. Tensile strength values obtained after bending were above the minimum limit (621MPa) established for grade X80 by the API 5L norm, showing that these microstructural changes promoted by the bending process do not compromise the structural integrity of the joint.
Cooling Process for Precipitation Strengthening of Vanadium in Ferrite
Authors: Cai Xiao Hui , Liu Zhen Yu , Wang Guo Dong
Published: January 2012

The precipitation of vanadium takes place mainly in ferrite by interphase precipitation or nucleation on dislocation line, which makes sense for the industry production due to the precipitation strengthening. The objective is to analysize the cooling process of V-steels to exert the precipitation strengthening of vanadium. The steels with 0.09%C-0.055%N/0.0107%N/0.0168%N/0.0193%N-0.08%V/0.085V steel are the researched steel grades. Using solid solubility products model and thermodynamic equation, the full solid solution temperature, nucleation rate curve and PTT curve of precipitation process are calculated. The effect of nitrogen on the precipitation behaviour of V(C,N) in γ and the precipitation of V(C,N) in α are simulated. Based on the calculation results the trial process is determined. The laboratorial trials are carried out with ultra fast cooling. The precipitate particles are observed by TEM. The solid solution amount increases monotonously and the size of precipitate particle decreases with the nitrogen content. The solid solution temperature of 0.055%N, 0.0107%N, 0.0168%N and 0.0193%N are 977.0°C, 1028.0°C, 1062.3 and 1078.9°C respectively. The laboratorial trial results shows that the tensile strength is improved about 100 MPa due to the precipitation strengthening. The relationship between the coiling temperature and the strength is parabolic curve downward and the relationship between the coiling temperature and the elongation is parabolic curve upward. This calculation can determine both the proper nitrogen content and the optimal cooling process. The trial results proves this method is feasible and efficiency.
Theoretical and Experimental Analysis of the Cooling Ability of Device for the Plain Round Bars Accelerated Cooling Process
Authors: Laber Konrad Błażej , Dyja Henryk , Kwapisz Marcin
Published: January 2012

The paper presents the results of the numerical modelling and industrial research of the cooling ability of the device for the round plain bars accelerated cooling process. Research were carried out for one of the bar rolling mill technological conditions in a few variants. The paper purpose was determination of the cooling ability of device for accelerated cooling process to checking possibility of the using this device in the rolling line, during normalizing rolling process. Investigation results elaborated in the paper made the basis for determination of the heat exchange coefficients between cooled band and water. In the next stage of this paper numerical modeling of the normalizing rolling process with accelerated cooling of band in the final stage of the rolling process was carried out. In this investigation heat exchange coefficients between band and cooling medium (water), which were determinated with allowance of cooling possibilities of investigated device for band accelerated cooling were used. From the obtained results it was found that in the analysed bar rolling mill it is possible to decrease the band average temperature to about 900 °C, which is required during the normalizing rolling process.
Modeling of the Influence of Admixing and Prealloying on the Optimisation of Compressibility and Sinter-Hardenability of Steel Powders
Authors: Giguère Nicolas , Blais Carl
Published: January 2012

The automotive industry applies pressure on the PM industry to produce components with superior mechanical properties at minimum cost. In this regard, sinter-hardenable powders are particularly well suited since they allow direct quenching of components at the end of the sintering cycle, thus eliminating the extra steps required for heat treating. This paper presents the results of the modeling of the influence of admixing and/or prealloying on the optimization of compressibility and hardenability of sinter-hardenable steel powders. A first design of experiments (DOE) was used to optimize the chemical composition and to study the interactions between prealloyed elements (Nickel, Chromium, Molybdenum and Manganese) and admixed elements (Nickel, Chromium, Manganese and Copper) on hardenability and compressibility. A second DOE was generated based on the results obtained in the first series. Results show that among all of the examined alloying elements, only prealloyed nickel, chromium and molybdenum had a significant effect on compressibility and hardenability. Moreover, within the range of concentrations under study, the optimum sinter-hardenable powder had the following (prealloyed) chemistry: 1.5 wt-% Ni, 0.55 wt-% Cr and 1.25 wt-% Mo.