bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Simulation of Microstructure Evolution of Cast Mg Alloy
Authors: Huo Liang , Han Zhi Qiang , Liu Bai Cheng
Published: January 2010

A cellular automaton (CA) model has been developed for simulating the microstructure evolution and dendrite morphology of cast magnesium alloys. The growth kinetics of dendrite tips is determined by the difference between local equilibrium composition and local actual composition obtained by solving the solute transport equation. Two sets of meshes, a hexagonal mesh and an orthogonal mesh, are used in the model to perform the simulation. The hexagonal mesh is used to perform CA calculation to reflect the texture of Mg alloy dendrites, and the orthogonal mesh is used to solve the solute transport equations. The model was applied to simulate single dendrite evolution and columnar dendrites growth of AZ91D Mg alloy, as well as multi-grain growth of Mg-10Gd-2Y-0.5Zr (wt%) Mg alloy. Permanent mold step-shaped castings of the two Mg alloys were poured and metallographic examinations were carried out for validating the present model. The simulation results agree well with metallographic results. The model can be applied to simulate the microstructure evolution and dendrite morphology of magnesium alloys.
Anomalous Characteristics of Ti-Nb-Ta-Zr Alloy for Biomedical Applications
Authors: Niinomi Mitsuo , Nakai Masaaki , Akahori Toshikazu , Tsutsumi Harumi
Published: January 2010

Negative thermal expansion, i.e. a type of shrinkage that occurs during heating, was observed in cold-rolled Ti-29Nb-13Ta-4.6Zr alloy (mass%) (TNTZ). The reduction ratio of cold rolling was systematically changed, and then the thermal expansion rate was measured using a dilatometer. The cyclicity of thermal expansion was also examined for the cold-rolled TNTZ. Further, the effect of oxygen content on the thermal expansion behavior of the cold rolled TNTZ was examined. With an increase in the reduction ratio of cold rolling, the thermal expansion rate of TNTZ cold-rolled parallel to the rolling direction (RD) decreases, but it increases in TNTZ cold-rolled parallel to the transverse direction (TD). The cyclicity of above-mentioned anomalous thermal expansion is observed in a temperature range below 473 K, but it is not observed when the specimen is heated to above 573 K in the first cycle. The oxygen suppresses the negative thermal expansion behavior of TNTZ.
Structure and Hardness of Martensite in Quenched Fe-C Steels
Authors: Sherby Oleg D. , Wadsworth J. , Lesuer D.R. , Syn C.K.
Published: January 2010

The exceptional high hardness of lath martensite in quenched Fe-C steels is explained by the Engel-Brewer valence electron theory for crystal structures. The theory predicts the transformation sequence FCC-HCP-BCC with FCC iron as Fe3v, HCP iron as Fe2v, BCC iron as Fe1v and carbon as C4v. Electronic compatibility requires transformation from FCC to HCP to form two separate components. Carbon-rich clusters of C4v with 8 Fe3v atoms are distributed uniformly in a carbon-free matrix of HCP Fe2v atoms. The carbon-iron clusters are viewed as particle-like, calculated as 0.63 nm in size, and is responsible for the high strength of martensite. The carbon-free region experiences shear deformation during FCC to HCP transformation leading to work hardened fine grains. Subsequent transformation to BCC iron maintains the same size carbon cluster with additional shearing deformation during HCP to BCC formation in the carbon-free region. Tempering studies of quenched martensite are shown to support the carbon-iron cluster model.
In Situ Observation of Solidification of Bulk Metallic Glass Forming Alloys from Supercooled Liquid by Using High Energy X-Ray Diffraction Combined with Levitation Techniques
Authors: Watanabe Masahito , Mizuno Akitoshi , Akimoto Toshihiko , Kohara Shinji
Published: January 2010

It is well known that multi-component alloys form bulk metallic glasses (BMGs) from the supercooled liquid state without rapid quenching. However, the mechanism of phase selection between crystal and glass states has not been fully clarified. To obtain an insight into the glass-forming processes, we carried out in-situ observation on the solidification of Zr-based BMG-forming alloys from its supercooled liquids by time-resolved X-ray diffraction combined with the conical nozzle levitation (CNL) technique to achieve a containerless melting. For Zr-based alloys, we succeeded in detecting the X-ray diffraction patterns during glass formation from the supercooled liquid state as well as the crystallization from the liquid state. Furthermore we performed the precise structure analysis of supercooled state of Zr-based binary liquids. Based on the liquid structure and in-situ observation results, we discussed about the phase selection mechanism between crystal and glass states.
Effect of Carbon and Nitrogen on the Hall-Petch Coefficient of Ferritic Iron (Review on the Hall-Petch Relation in Ferritic Iron)
Authors: Takaki Setsuo
Published: January 2010

Grain size dependence of yield strength was reviewed for polycrystalline ferritic iron and low carbon steel. Yielding of polycrystalline low carbon steels was characterized by a clear yield point (upper yield point) and such a yielding behavior is taken over to ultra fine grained steel with the grain size below 1m. Yield strength (y) of polycrystalline low carbon steels obeys the Hall-Petch relation: y[MPa]=+600×d[m]-1/2 . The Hall-Petch coefficient ky is around 600 MPa･m1/2 for the commercial low carbon steels but it is lowered to about 100 MPa･m1/2 for interstitial fee steel. Besides, it is known in industrial pure iron (Fe-30ppmC) that ky increases with aging at 363K. The value of ky is also increases with increasing the amount of solute carbon content. The ky is enlarged from 100 MPa･m1/2 to 550 MPa･m1/2 by adding 60ppm of solute carbon and then levels off at around 600 MPa･m1/2 in the carbon concentration region above 60ppm. On the other hand, nitrogen hardly influences the ky value. Difference between C and N in the contribution to ky is probably due to the difference in grain boundary segregation behavior. Macroscopic yielding of polycrystalline ferritic iron is reasonably explained by the Hall-Petch model considering dislocation pile-up against grain boundary and dislocation emission from the grain boundary where stress concentration has been generated by piled up dislocations. It is seemed that the segregated carbon stabilized the dislocation emission site at grain boundary and this leads to the increase in ky.
Formation of High Density Metal Silicide Nanodots on Ultrathin SiO2 for Floating Gate Memory Application
Authors: Miyazaki Seiichi , Ikeda Mitsuhisa , Makihara Katsunori , Shimanoe K. , Matsumoto R.
Published: January 2010

Nickel- and Platinum-silicide nanodots with an areal density of the order of ~1011cm-2 were successfully formed on thermally-grown SiO2 through a process of ultrathin metal film formation on self-assembled Si quantum dots (QDs) on SiO2 and subsequent remote H2 plasma exposure. Chemical shifts in photoemission spectra of core lines and changes in valence band spectrum and work function value with the remote H2-plasma treatment show that silicidation of pre-grown Si-QDs is promoted by the remote H2-plasma treatment. Electrical separation among so-prepared nanodots was verified from the surface potential change after applying a dc bias between the AFM tip and the sample surface. From temporal decay in the surface potential after electron injection to the nanodots, we confirmed that silicide nanodots have superior charge retention to that of Si nanodots with almost the same size as expected in a deeper potential well for electrons in silicide dots than pure Si-QDs. In the application of silicide nanodots to a floating gate in MOS capacitors, distinct hysteresis characteristics caused by charging and discharging of several electrons per dot were verified by capacitance-voltage measurements.
Characterization and Sintering Behaviors of Fe Based Nanopowders Prepared by Arc Discharge Process
Authors: Choi C.J. , Yu J.H. , Lee Jung Goo
Published: January 2010

The formation of Fe nanopowders by Plasma Arc discharge process and sintering behavior of Fe nanopowder has been investigated. The effect of processing parameters on the size and microstructure and their pressureless sintering behaviors have been analyzed. Also the addition effect of micron powder to nanopowder on the compaction and sintering was studied. The prepared Fe nanpowder showed nearly spherical shape with the average size of 100 nm. The surface oxide layer of nanopowder played an important role on the initial densification of the green compact. The hardness and sintered density of nano/micron bimodal powder was similar to those of pure nanopowder.
Effect of Die Temperature on Mechanical Properties of Hot Pressed P/M Parts
Authors: Babakhani Abolfazl , Haerian Ali
Published: January 2010

In conventional warm compaction, both powder and die are heated to a certain temperature during compaction. This is a technique for producing P/M compacts with higher green and sintered strength as compared to room temperature pressing. However, there is a certain limit to powder temperature due to flow problems at higher temperatures. Heating the die above this practical limit can further improve properties. In this work, the effect of die temperature on green and sintered properties of Astaloy CrM powder has been investigated. Here, the powder at 135 oC was fed to the die at different temperatures. Density and strength for samples in green and sintered conditions were evaluated for two compaction pressures of 500 and 650MPa and temperatures ranging from ranging from 135 to 165 oC. Comparison of samples compressed at room temperature showed marked improvement in density and strength properties. A 22% increase in density, as well as 40% increase in green strength was observed. Tensile and impact strengths were improved by about 10% and 20% respectively. SEM micrographs showed more rounded pores and hence reduced stress raising sites. The improvement in properties can be mainly attributed to changes in powder morphology and die wall lubrication due to migration of hot lubricant from interparticle space to die walls. The latter will reduce particle spacing and bring about more intimate metal-metal contacts as well as better lubrication on die walls.
Heat Transfer and Fluid Flow in Sintered Metallic Fiber Structures
Authors: Andersen Olaf , Meinert Jens
Published: January 2010

Sintered metal fiber structures show a favourable ratio between pressure drop and inner surface area. Their exclusively open-cell morphology makes them well suited for heat transfer or temporary heat storage applications. Recently, highly conductive sintered metal fiber structures were successfully prepared from melt extracted aluminum alloy fibers. The heat conduction and fluid flow properties of metallic sintered short fiber structures were determined experimentally and compared with simple analytical models. It was found that equations taken from the available literature yield good approximations to the experimental results.
Grain Refinement of Vanadium by Low Temperature Severe Plastic Deformation
Authors: Chun Y.B. , Ahn S.H. , Shin D.H. , Hwang S.K.
Published: January 2010

Recent advances in the severe plastic deformation technique have shown that effective refinement of the microstructure can be achieved in pure metals as well as in alloys. Among the various methods of severe plastic deformation, equal channel angular pressing has been the subject of numerous research works. Since the grain refining effect of this technique appears to reach a peak at a level of approximately 200 nm further microstructural changes are sought—deformation at a cryogenic temperature being one of the candidate routes. In the present study, we opted to combine equal channel angular pressing and low temperature plastic deformation to refine the microstructure of commercially pure V. The starting microstructure consisted of equiaxed grains with an average size of 100 micrometers. This microstructure was refined to a 200 nm thick lamellar microstructure by 8 passes of equal channel angular pressing at 350°C. The lamellar thickness was further reduced to 140 nm upon subsequent cryogenic rolling, which resulted in room temperature yield strength of 768 MPa. In the specimens, recrystallization annealed at 850°C, the grain size reached 1000 nm or larger, and the yield strength obeyed the Hall-Petch relationship with that grain size. The tensile elongation value, which was low and insensitive to the grain size in the as-deformed state, increased significantly up to 43% with the recrystallization annealing.
On the Utilization of Plastic Instability Criterion in Ductility Assessment of Ultrafine-Grained Microalloyed Steel
Authors: Majta Janusz , Doniec Karolina , Muszka Krzysztof
Published: January 2010

In the present study, ultrafine-grained (UFG: grain size < 1m) HSLA and IF steels were investigated. The tensile test results showed that, because of different strengthening mechanisms, UFG HSLA steel represents finally better ductility than initially more ductile IF steel. The analysis performed in the present study is based on the mechanism of generation the dislocation structures and takes into account effects of precipitation and solid solution strengthening. The results of this analysis, implemented in FEM, enable to capture the moment of plastic instability of ultrafine-grained microalloyed steels. A good convergence of the proposed model was observed for the investigated steels. The fact that ductility, strengthening and deformation mechanisms are strictly connected to each other suggests that the proper use of their synergetic effect may be used to improve the ductility of UFG materials.
Advances in Thin Film Technology through the Application of Modulated Pulse Power Sputtering
Authors: Mishra Brajendra , Moore J.J. , Lin Jian Liang , Sproul W.D.
Published: January 2010

High power pulsed magnetron sputtering (HPPMS) is an emerging thin film deposition technology that generate high ionization plasma by applying a very large amount of peak power to a sputtering target for a short period of time. HPPMS is also known as High Power Impulse Magnetron Sputtering (HiPIMS). However, HPPMS/HiPIMS exhibits decreased deposition rate as compared to continuous dc magnetron sputtering. Modulated pulse power (MPP) magnetron sputtering is an alternative HPPIMS deposition technique that overcomes the rate loss problem while still achieving a high degree of ionization of the sputtered material. In the present work, the principles and some important characteristics of MPP technology were presented. Technical examples of CrN coatings were deposited using MPP and continuous dc sources. The positive ion mass distributions were characterized using an electrostatic quadrupole plasma mass spectrometer. The structure and properties of MPP and dc CrN coatings were characterized using x-ray diffraction, scanning electron microscopy, nanoindentation tests, and ball-on-disc wear test. It was found that the MPP CrN coating exhibits denser microstructure and improved mechanical and tribological properties as compared to the dc CrN coating.
Preparation of Ti-Based and Zr-Based Bio-Metallic Wires by Arc-Melting Type Melt-Extraction Method
Authors: Nagase Takeshi , Kinoshita Koichi , Nakano Takayoshi , Umakoshi Yukichi , Niinomi Mitsuo
Published: January 2010

New Ti-based and Zr-based metallic wires for the future application as biomaterials were developed by arc-melting type melt-extraction method. Zr-based metallic glass wire, -Ti type Ti-Zr binary wire and -Ti type Ti-Nb-Ta-Zr (TNTZ) wire show high tensile strength and good vending ductility. Zr-based metallic glass wire shows extremely high tensile strength over 1GPa and large elastic strain limit reached approximately 2%. Ti-Zr binary alloy shows high wire-shape forming tendency during melt-extraction, and high Ti concentration Ti90Zr10 alloy wire was obtained. TNTZ wire shows superior bending ductility and full ductility is achieved.
Properties of New TiC/TiB2/Fe-Al Cermet Alloy
Authors: Nakayama Hiroyuki , Tada Shuji , Masashi Mikami , Ozaki Kimihiro , Kobayashi Keizo
Published: January 2010

Effect of TiB2 substitution on thermal conductivity and hardness in TiC / Fe-Al cermets was investigated. The (70-x)TiC / xTiB2 / 26Fe-4Al mass % cermets were fabricated by mechanical milling and subsequent pulsed current sintering method. The high relative density compacts was formed by sintering at 1423 K under 25 MPa for 60 s. The sintered materials were mainly composed of TiC, TiB2 and Fe-Al intermetallic compound. In addition, small amounts of Fe2B surrounding TiB2 were formed. The thermal conductivity of the sintered compact lineally increased with increasing TiB2 volume fraction. However, the hardness of the sintered compacts of x = 20 – 40 were higher than that of x = 0. Therefore, the substitution of TiC to TiB2 in the TiC / Fe-Al based cermet is effective to improve the thermal conductivity without the degradation of hardness.
Influence of Plastic Deformation on Recrystallized Microstructure of Fe-Base ODS Alloy
Authors: Capdevila Carlos , Toda I. , Chao J. , García de Andrés Carlos
Published: January 2010

The ferritic oxide dispersion strengthened alloys (ODS) are manufactured using the mechanical alloying process. The development of a coarse grained microstructure during the recrystallization has been noted and discussed by a number of authors but, the mechanism of grain control remains uncertain. Recent work has emphasized the large influence of non-uniformities on the development of the recrystallized microstructure. The purpose of the present work was to study the effect of non-uniform plastic strain on recrystallization of Fe-base ODS alloy named MA 957.
Two-Phase Microstructures Formed by Phase-Separation of Coherent Precipitates in Elastically Constrained Alloy Systems
Authors: Doi Minoru
Published: January 2010

Coherent two-phase microstructures consisting of ordered precipitate and disordered matrix phases sometimes exhibit a phase-separation, which brings the split and/or the decelerated coarsening of precipitates. When the coherent two-phase microstructure of A1+L12 (+’) in Ni-base alloys are aged inside the two-phase region of A1+L12 , the L12 precipitate sometimes exhibit a phase-separation and A1 phase newly appears and grows in each L12 precipitate. Phase-separations of the same type to the above also take place due to ageing of coherent two-phase microstructures of A2+D03 and A2+B2 in Fe-base alloys: D03 and B2 precipitates sometimes exhibit phase-separations and A2 phase newly appears and grows in both precipitates. These types of phase-separation take place under the influence of chemical free energy. In the course of further ageing, the new disordered phases of A1 and A2 change their morphology in various ways depending on the elastic constraint: i.e. the morphology of new A1 or A2 phase is influenced by the elastic energies and the surface energy.
Characterisation of the Structure of Single-Crystal Nickel-Base Superalloys
Authors: Epishin Alexander , Link Thomas , Brückner Udo
Published: January 2010

New experimental methods developed by the authors for characterisation of the structure of single-crystal nickel-base superalloys are presented: X-ray diffraction at defined areas of the dendritic structure, none destructive SEM investigation of ’-morphology changes for different creep stresses and times with one specimen, and high resolution SEM investigations of dislocations in the ’-interfaces. Application of these techniques allowed to obtain new results, e.g. about the mosaicity of dendritic subgrains, distribution of the ’-misfit within a single dendrite and kinetics of rafting during creep in the superalloy CMSX-4 in wide temperature and stress ranges.
FE Analysis of Microstructure Evolution during Ring Rolling Process of a Large-Scale Ti-6Al-4V Alloy Ring
Authors: Yeom Jong Taek , Kim Jeoung Han , Hong Jae Keun , Park Nho Kwang , Lee Chong Soo
Published: January 2010

Microstructure evolution during ring rolling process of a large-scale Ti-6Al-4V ring was investigated with the combined approaches of three dimensional finite element method (FEM) simulation and microstructure prediction model. A microstructure prediction model was established by considering the volume fractions and grain size of  and  phases varying with process variables, and grain growth. In order to perform FE simulation for ring rolling process of Ti-6Al-4V alloy, a constitutive equation was generated by utilizing the flow stress data obtained from hot compression tests at different temperature and strain rate conditions. The volume fraction and grain size of  and  phases during ring rolling were calculated by de-coupled approach between FEM analysis and microstructure prediction model. The prediction results were compared with the experimental ones. Our proposed microstructure simulation module was useful for designing hot forming process of Ti-6Al-4V alloy
Effects of Surface Recrystallization on the Microstructures and Creep Properties of Single Crystal Superalloy DD6
Authors: Li Jia Rong , Sun Feng Li , Xiong Ji Chun , Liu Shi Zhong , Han Mei
Published: January 2010

This work assesses the effects of the surface recrystallization of the processing of water grit blasting, grit blasting and mechanically polishing on the microstructures and creep rupture properties of DD6 alloy, a low-cost second generation single crystal superalloy. The results demonstrate that the possibility and the depth of the surface recrystallization of DD6 show an increase as the annealing temperature increases from 1050°C to 1250°C. No surface recrystallization happens when the specimens of the alloy have been undergone at 1100°C for 4 hours after water grit blasting, but the surface recrystallization occurs at the annealing temperature above 1200°C for 4 hours after water grit blasting. The test indicates that the increasing pre-deformation decreases the surface recrystallization temperature. The creep rupture life of DD6 alloy without processing is 274.4 hours, 341.1 hours at the conditions of 980°C/250MPa, 1070°C/140MPa respectively. After annealing at 1100°C for 4 hours, the creep rupture life of the alloy with the processing of water grit blasting is equivalent to that of the alloy without processing. The surface recrystallization of the alloy happens with the processing of grit blasting after the annealing at 1100°C for 4 hours, and there is a reduction of the creep rupture life at the conditions as mentioned above. The creep properties of DD6 alloy meet the needs of blades and vanes of single crystal for advanced aeroengines when the surface recrystallization of the alloy occurs during manufacturing and processing.
Modeling Grain Boundary Mobility during Dynamic Recrystallization of Metallic Alloys
Authors: Montheillet Frank , Damamme Gilles , Piot David , Semiatin S. Lee
Published: January 2010

A simple analytical model is proposed for estimating grain boundary mobility during dynamic recrystallization in metallic alloys. The combined effects of solutes (solute drag) and second phase particles (Zener pinning) on mobility are considered. The approach is based on (and is consistent with) a recently published mesoscale model of discontinuous dynamic recrystallization. The dependence of grain boundary mobility on solute concentration and particle size is summarized in the form of two-dimensional maps.
Dynamic Recrystallization Modeling during Hot Forging of a Nickel Based Superalloy
Authors: Solas Denis , Thébault Julien , Rey Colette , Baudin Thierry
Published: January 2010

A crystalline modeling of deformation implemented in the Finite Element code Abaqus® coupled to a recrystallization Cellular Automaton code is proposed and applied to the hot forging process. A sequential modeling is used in order to obtain a better understanding of the experimental observations and to improve our knowledge of the dynamic recrystallization process.
Modeling is performed on aggregates built up from Electron Back Scattered Diffraction measurements. At the deformation temperature, the material presents two phases with a γ matrix of FCC structure and a γ’ hardening phase under a precipitate shape (Ni3(Ti,Al)) of SC structure. The crystalline approach can describe the interactions between the two phases and can compute the evolution of the local strain and stress fields as well as the dislocation density and the lattice rotation in the different grains. A Cellular Automaton algorithm is used for simulating the microstructure evolution during dynamic recrystallization. Nucleation and grain boundary mobility depend on the misorientation and on the local variation in stored energy.
This presentation mainly details the different assumptions introduced in the recrystallization code and their influences on the microstructure evolution.
Directional Diffusion and Effect Factors of the Elements during Creep of Nickel-Base Single Crystal Superalloys
Authors: Tian Su Gui , Wang Ming Gang , Yu Xing Fu , Lu Xu Dong , Qian Ben Jiang
Published: January 2010

By means of the calculation of the elements diffusion mobility, an investigation has been made into the influence of the elements interaction on the rates of the elements diffusion and  phase directional coarsening during creep of single crystal superalloys. Results show that the elements diffusion and  phase directional coarsening during creep are related to the applied stressed and elastic modulus. And the rate of  phase directional coarsening is enhanced with the applied stresses. Due to the interaction between the elements, the rates of the elements diffusion and  phase directional coarsening decrease with the increment of the elements Ta+Mo gross and Ta/W ratio. In the diffusion field of the elements during creep, the Al, Ta atoms with bigger radius are diffused to {100} planes to form the N-type rafted structure along the direction vertical to the applied stress axis, and the change of the strain energy density in the interfaces of the cubic  phase is thougth to be the driving force of the elements diffusion.
Microstructure and Processing Ability of β-Solidifying TNM-Based γ-TiAl Alloys
Authors: Imayev V.M. , Imayev Renat M. , Khismatullin Timur G. , Oleneva T. , Gühter Volker , Fecht Hans Jörg
Published: January 2010

Microstructure and hot workability have been considered for a number of -TiAl alloys including -solidifying TNM alloys. All TNM alloys under study showed improved hot workability in cast condition. As was shown for the Ti-45Al-5Nb-1Mo-0.2B alloy, a critical issue of TNM alloys is room temperature ductility in the conditions with lamellar structure.
Dynamic Recrystallization Behavior of GH4586 Superalloy during Hot Compression
Authors: Wang Lei , Wang Shu Ai , Liu Yang , Zhao Guang Pu
Published: January 2010

Compression test for GH4586 superalloy was carried out at 1273 K and 1373 K with stain from 20% to 60%. The characteristics of dynamic recrystallization were investigated by confocal laser scanning microscope, TEM and EBSD. It was found that at 1273 K dynamic recrystallization mainly took place along preexisting grain boundaries creating a necklace structure. It was confirmed by TEM observations that the first layer of the necklace structure was formed by the mechanism of bulging of preexisting grain boundaries and the following layers were nucleated at the triple junctions of former dynamic recrystallization grains. When specimens were deformed with different strains at 1373 K, dynamic recrystallization was almost completed. Our observation showed that twinning played an important role during dynamic recrystallization by promoting dynamic recrystallization grains growing. Substructures of grains were constructed by the reconfiguration of dislocations hindered at large ' particles in interior of initial grains during dynamic recovery.
The Precipitation Strengthening Effect of Nb, Ti and Al in Cast/Wrought Ni-Base Superalloys
Authors: Xie Xi Shan , Fu Shu Hong , Zhao Shuang Qun , Dong Jian Xin
Published: January 2010

The second phase precipitation strengthening effect of , +, + phases in INCONEL718 type and newly developed INCONEL740® Ni-base superalloys and their structure stability have been studied. Experimental results show that careful control of Nb, Ti and Al for alloy modification can not only raise their strengths but also improve structure stability at high temperatures. These modified newly developed alloys are suggested to be used at higher temperatures.
Residual Stress in PVD-Coated Carbide Cutting Inserts - Applications of the sin2ψ and the Scattering Vector Method
Authors: Denkena Berend , Erkens Georg , Breidenstein Bernd
Published: January 2010

Premature collapse in terms of cohesive damage of PVD-coated carbide cutting tools often results in a time and cost consuming immediate interrupt of the cutting process. It is assumed that the residual stress state of the composite coating – substrate in combination with external loads during tool use is responsible for cohesive damage. The X-ray diffraction methods sin2 and scattering vector are applied for determination of the residual stress depth distribution in the coating and the substrate’s subsurface. Investigations of the residual stress state of commercial PVD-coated carbide cutting tools are presented. It is determined to what extent the single process steps during tool manufacturing are responsible for the final residual stress state of the PVD-coated tool. Furthermore the meaning of the PVD-coating process for the substrate’s residual stress state is investigated. Moreover, possibilities of controlling the residual stress state of the substrate by changing process variables of selected process steps are analyzed.
Thermomechanical Treatment of Aluminum Alloy Fin Stock for Heat Exchanger Produced by Twin Roll Strip Casting Process
Authors: Kang Suk Bong , Kim Dong Bae , Jung Sang Su , Euh Kwang Jun
Published: January 2010

Aluminum alloys are commonly used as a material for heat exchangers due to their higher thermal conductivity and specific strength among various metallic materials. The lightweightening heat exchangers for automobile application are requisite for reducing the evolution of CO2 and improving the efficiency of fuel. The twin roll strip casting process is considered to produce the high quality and low manufacturing cost aluminum alloy fin stock for automobile heat exchangers. Thermomechamical treatment has carried out to obtain optimum processes for initial cold rolling, intermediate annealing and final cold rolling, which can meet the requirements for high strength and high thermal conductivity after brazing heat treatment. Mechanical properties and thermal condutivity have been evaluated before and after simulated brazing process. The nuclei of recrystallization might be formed along shear deformation bands during initial cold rolling and should be grown during intermediate annealing to enhance the permeation of molten brazings for the following brazing process. Final cold rolling has allowed strain hardening and controlling of sagging amount as fin stock materials of heat exchanger. In the present study the suitable thermomechnical treatment was suggested to balance the properties of strength, thermal conductivity, brazing behavior and sagging in Al-Fe-Mn-Si-Zn based alloys produced by twin roll strip casting process.
Residual Stresses Relaxation Caused by Pulsed Electric Current
Authors: Stepanov Gennadiy , Babutsky Anatoli , Kruszka Leopold
Published: January 2010

The results of investigations of the influence of the treatment based on a direct passage of pulsed electric current of high density through the simple parts with a copper-composite joint, coatings and a grinded surface causing residual stress relaxation and redistribution of the stresses are presented in the paper.
Residual Stress Measurement by Neutron Diffraction in a Single Bead on Plate Weld - Influence of Instrument and Measurement Settings on the Scatter of the Results
Authors: Ohms Carsten , Wimpory Robert C. , Neov Dimitar
Published: January 2010

Residual stress measurements on a single bead weld on a steel plate had been performed at the High Flux Reactor of the Joint Research Centre in 2003. For these measurements a relatively old diffractometer had been used. The results obtained were characterized by significant scatter of the data, and the measurement quality suffered from the short movement ranges of the specimen positioning table as well.
In 2008, a second, nominally identical, specimen from the same activity was investigated on a second diffractometer, which allowed the repetition of the residual stress measurements using different measurement settings. The present paper compares the old and the new measurement results, with a view to assessing the impact of the instrumental settings on their quality. It has been found that the overall stress distributions from the 2003 and the 2008 measurements were in fact very similar. Nevertheless, the new settings used, such as in-situ specimen rocking, extended measurement duration, increased density of measurement positions and spatial resolution among others, have been found to have considerable impact on the real and on the apparent scatter of the experimental results showing that the presented methodologies can be used for improvement of neutron diffraction measurements.
The New GKSS Materials Science Beamlines at DESY: Recent Results and Future Options
Authors: Staron Peter , Schell Norbert , Haibel Astrid , Beckmann Felix , Lippmann Thomas , Lottermoser Lars , Herzen Julia , Fischer Torben , Koçak Mustafa , Schreyer Andreas
Published: January 2010

GKSS is currently investing heavily into new beamlines at DESY in Hamburg, Germany. After the completed installation of the wiggler beamline HARWI II at DORIS III GKSS is now building two new undulator beamlines at the new PETRA III storage ring. The High Energy Materials Science Beamline (HEMS) will allow high resolution diffraction experiments using samples and sample environments with masses up to 1 t, 3DXRD measurements, and high-energy micro-tomography experiments. The Imaging Beamline (IBL) will provide a nano-tomography as well as a micro-tomography station for X-ray energies up to 50 keV. Examples of typical experiments in the field of residual stress analysis, micro-tomography, and high-energy small-angle X-ray scattering will be given.
A Model of Discontinuous Dynamic Recrystallization and its Application for Nickel Alloys
Authors: Damamme Gilles , Piot David , Montheillet Frank , Semiatin S. Lee
Published: January 2010

A simple mesoscale model was developed for discontinuous dynamic recrystallization. The material is described on a grain scale as a set of (variable) spherical grains. Each grain is characterized by two internal variables: its diameter and dislocation density (assumed homogeneous within the grain). Each grain is then considered in turn as an inclusion, embedded in a homogeneous equivalent matrix, the properties of which are obtained by averaging over all the grains. The model includes: (i) a grain boundary migration equation driving the evolution of grain size via the mobility of grain boundaries, which is coupled with (ii) a dislocation-density evolution equation, such as the Yoshie–Laasraoui–Jonas or Kocks–Mecking relationship, involving strain hardening and dynamic recovery, and (iii) an equation governing the total number of grains in the system due to the nucleation of new grains. The model can be used to predict transient and steady-state flow stresses, recrystallized fractions, and grain-size distributions. A method to fit the model coefficients is also described. The application of the model to pure Ni is presented.
Variational Aspects of the Physically-Based Approach to 3D Non-Local Continuum Mechanics
Authors: Di Paola Mario , Zingales Massimiliano
Published: January 2010

This paper deals with the generalization to three-dimensional elasticity of the physically-based approach to non-local mechanics, recently proposed by the authors in one-dimensional case. The proposed model assumes that the equilibrium of a volume element is attained by contact forces between adjacent elements and by long-range central forces exerted by non-adjacent elements. Specifically, the long-range forces are modeled as central body forces depending on the relative displacements between the centroids of the volume elements, measured along the line connecting the centroids. Furthermore, the long-range forces are assumed to be proportional to a proper, material-dependent, distance-decaying function and to the products of the interacting volumes. Consistently with the modeling of the long-range forces as central body forces, the static boundary conditions enforced on the free surface of the solid involve only local stress due to contact forces. The model coalesces with the well-known Kröner-Eringen (KE) integral model of non-local elasticity for unbounded domains but it remains substantially different in case of bounded domain.
Continuous Casting and Rolling for Aluminum Alloy Wire and Rod
Authors: Kim Myoung Gyun , Lee Gyu Chang , Park Joon Pyo
Published: January 2010

Since the Continuous Casting & Rolling of the non-ferrous metal by Illario Properzi have invented in 1944, the various non-ferrous rod, wire and sheet are produced at present. Although there is long research and trials for producing the wire or rod of commercial the high-strength aluminum alloy, there are few companies with the success in producing commercial hard-aluminum alloys wire and rod by CC&R process. The application of the high-strength aluminum alloy rod or wire is various parts such as rivet, bolt, sports leisure supplies, high-tension power transmission wire, machinable and forgeable materials. However, it is very difficult to produce the high-strength aluminum alloy wire and rod by CC&R process because of the wide mushy zone and high strength compared with the pure or low strength aluminum alloy. Additionally, it is easy to crack and breakout in casting and rolling process due to tiny internal defects of the castings. The object of this project is to design the most suitable equipments for CC&R and optimize the experimental condition of continuous casting condition of the high-strength aluminum alloy. The facilities of CC&R process in RIST are composed of the melting furnace, the wheel casting machine, the automatic machine for moving of castings bar, the 15-step rolling machine with three rolls, the induction heater for reheating the castings bar and the coiling machine. In the present work, through the numerical computer simulation, in first, we have developed the thermal model of the solidification behavior of the casting bar. Finally, using finite element code, Marc, the temperature distribution of each rolled bar and effective strain are obtained during continuous rolling.
Modeling the Effect of Stress and Plastic Strain on Martensite Transformation
Authors: Maalekian Mehran , Kozeschnik Ernst
Published: January 2010

The influence of compressive stress up to 250 MPa and plastic deformation of austenite on the martensite transformation behavior of a eutectoid steel is studied both experimentally and theoretically. It is demonstrated that martensite formation is assisted by stress but it is retarded when transformation occurs from plastically deformed austenite. With the quantitative modeling of the problem based on the theory of displacive shear transformation, the explanation of contradicting observations is presented.
Sensitivity Analysis as a Tool of Optimal Sensors Location for Solidification Parameters Estimation
Authors: Majchrzak Ewa , Mendakiewicz Jerzy
Published: January 2010

The paper deals with the inverse problems appearing in the thermal theory of foundry processes. In particular, the problems connected with identification of casting and mould thermophysical parameters can be considered. To estimate the parameters determining heat transfer processes in the system casting-mould, the additional information concerning the changes of temperature at the points selected from the domain considered is necessary. The localization of sensors should assure the best conditions of identification process. Generally speaking, the sensor should be located at the point for which the sensitivity of temperature field with respect to parameter estimated achieves maximum. In the case of simultaneous identification of several parameters, the proper choice of sensors localization is more complicated. The main goal of the paper is to discuss a theoretical base connected with the problem formulated, to present the possibilities of numerical methods application, to solve the problem, and finally to show the examples of inverse problems solutions (in particular, the latent heat of binary alloy will be estimated).
Strength of Alloyed Metal Castings Using Multiphase Models and Non-Linear FEM
Authors: Martikka Heikki , Pöllänen Ilkka
Published: January 2010

High chromium cast iron material 1.4405 GX4CrNiMo 16-5-1 is successfully used in chemical process industry components loaded with hot, highly corrosive and abrasive at high pressures. Overheating test made a discontinuous yielding knee to appear caused probably by dissolution of carbon containing smaller phases but the overall strength and ductility are not affected. Microstructures are studied by optical and SEM microscopy and hardness measurements. This alloy has three main phases appearing as a mixture of rounded and lamellar phases. The work hardening behaviour is studied by analytical composite phase models and 2D FEM models with individual bilinear hardening phase models. The results agreed reasonably. FEM models showed the weak points of the alloy. Fit to test data was better with rounded phase than lamellar phase model. Combination of these tools is useful for innovative special alloy developments.
Iron Removal in Aluminum Melts Containing Scrap by Electromagnetic Stirring
Authors: Lee Gyu Chang , Kim Myoung Gyun , Park Joon Pyo , Kim Jong Ho , Jung Ju Hee , Baek Eung Ryul
Published: January 2010

Excessive iron in aluminum melt produces needle-shaped beta-AlFeSi intermetallic compounds during solidification. The presence of beta-AlFeSi intermetallic compounds can be harmful in the extrusion process because of the high pressure. As a common process, those compounds change from the needle-shaped to the globular-shaped alpha-AlFeMnSi intermetallic compounds through the addition of manganese to the aluminum melt. Those phases settle down during the solidification process, and then such is cut. Note, however, that the efficiency of iron elimination is very low. Our previous study reported that EMS can help the alpha-AlFeMnSi intermetallic compounds form easier and faster and settle down at the bottom of the aluminum melt through the centrifugal force of EMS. To investigate the effect on the efficiency of iron elimination in aluminum melt scrap, EMS current, holding temperature, and time of melt as well as the ratio of manganese to iron were controlled. As a result of this study, lower holding temperature and longer holding time of aluminum melt make iron elimination in aluminum melt more efficient with induced EMS. The best efficiency of iron elimination in aluminum melt was 65.2%with EMS induced at 923k for 4 minutes.
Numerical Thermo-Mechanical Modelling of Stress Fields and Residual Constraints in Metallic Targets Subject to Laser Shock Processing
Authors: Morales Furió Miguel , Molpeceres C. , Porro J.A. , García-Beltrán A. , Ocaña José Luis
Published: January 2010

In the analysis of the thermomechanical behaviour of the target material subject to Laser Shock Processing (LSP), most of the simplified models used for the analysis of its residual shocked state rely on rather simple estimations or material response equations that rarely take into account a detailed description of the material subject to a simultaneous dynamic compression and either deformation-induced or plasma-driven thermal heating.
The calculational system developed by the authors (SHOCKLAS) includes a coupled analysis of the pressure wave applied to the target material as a result of the plasma buildup following laser interaction and the shock wave propagation into the solid material with specific consideration of the material response to thermal and mechanical alterations induced by the propagating wave itself (i.e. effects as elastic-plastic deformation, changes in elastic constants, etc.). The model is applicable to the typical behaviour shown by the different materials through their dynamic strain-stress relations.
In the present paper, the key features and several typical results of the developed SHOCKLAS calculational system are presented. In particular, the application of the model to the realistic simulation (full 3D dependence, non linear material behaviour, thermal and mechanical effects, treatment over extended surfaces) of LSP treatments in the experimental conditions of the irradiation facility used by the authors is presented
The Use of Model Systems Based on Fe-30%Ni for Studying the Microstructural Evolution during the Hot Deformation of Austenite
Authors: Palmiere Eric J. , Bai F. , Poths R.M. , Turner J. , Nagarajan V. , Wynne Bradley P. , Rainforth W. Mark
Published: January 2010

The development of physically-based models of microstructural evolution during thermomechanical processing of metallic materials requires knowledge of the internal state variable data, such as microstructure, texture and dislocation substructure characteristics, over a range of processing conditions. This is a particular problem for steels, where transformation of the austenite to a variety of transformation products eradicates the hot deformed microstructure. This paper reports on a model Fe-30wt%Ni based alloy, which retains a stable austenitic structure at room temperature, and has therefore been used to model the development of austenite microstructure during hot deformation of conventional low carbon-manganese steels. It also provides an excellent model alloy system for microalloy additions. Evolution of the microstructure and crystallographic texture was characterised in detail using optical microscopy, XRD, SEM, EBSD, and TEM. The dislocation substructure has been quantified as a function of crystallographic texture component for a variety of deformation conditions for the Fe-30%Ni base alloy. An extension to this study, as the use of a microalloyed Fe-30% Ni-Nb alloy in which the strain-induced precipitation mechanism was studied directly. The work has shown that precipitation can occur at a much finer scale and higher number density than hitherto considered, but that pipe diffusion leads to rapid coarsening. The implications of this for model development are discussed.
Rheological Behavior of Pure Binary Ni–Nb Model Alloys
Authors: Piot David , Montheillet Frank , Semiatin S. Lee
Published: January 2010

This experimental work deals with the influence of niobium additions to high purity nickel on dynamic recrystallization behavior during hot working. Various high-purity alloys were prepared (unalloyed Ni and Ni–0.01, 0.1, 1 and 10 wt % Nb) and deformed to high strains by hot torsion tests to characterize the rheological behavior within the range 800 – 1000°C at strain rates of 0.03, 0.1 and 0.3 s–1. Niobium additions strongly increased the flow stress. To quantify such behavior, the strain-hardening parameter h and dynamic-recovery parameter r in the Yoshie-Laasraoui-Jonas constitutive equation were determined from the initial part of the experimental stress-strain curves (i.e., at strains before the stress peak) in which dynamic recrystallization does not alter the mechanical behavior. A table showing the variation of h and r as a function of strain rate, temperature, and niobium content was compiled and used to fit a simple empirical model for predicting h and r from the deformation conditions and alloy composition. In addition, microstructures were determined by optical metallography and SEM/EBSD. Based on this work, it appears that niobium additions noticeably refine the steady-state grain size by considerably decreasing the kinetics of dynamic recrystallization in nickel.