bluuebunny/crossref_metadata_2025 huggingface dataset:
Duplex Stainless Steel Microstructural Developments as Model Microstructures for Hot Ductility Investigations
Authors: Martin Guilhem , Véron Muriel , Chéhab B. , Fourmentin R. , Mithieux Jean Denis , Yerra S. K. , Delannay Laurent , Pardoen Thomas , Bréchet Yves J.M.
Published: July 2011

Duplex stainless steels (DSS) are alloys made of ferrite and austenite, with a proportion of each phase around 50%. Their main advantage in comparison with other austenitic and ferritic stainless steels is the attractive combination of high strength and corrosion resistance together with good formability and weldability. Unfortunately, DSS often present a poor hot workability. This phenomenon can stem from different factors associated to the balance of the phases, the nature of the interface, the distribution, size and shape of the second phase, and possibly also from difference in rheology between ferrite and austenite. In order to determine the specific influence of phase morphology on the hot-workability of DSS, two austenite morphologies (E: Equiaxed and W: Widmanstätten) with very similar phase ratio have been generated using appropriate heat treatments. It was checked that the latter treatments generate stable microstructures so that subsequent hot mechanical tests are performed on the microstructures of interest. One microstructure consists of a ferritic matrix with austenitic equiaxed islands while the other microstructure is composed of a ferritic matrix with Widmanstätten austenite. The latter morphology corresponds to the morphology observed in as-cast slabs.
Electron Microscopy Study of Hypostoichiometric Fe-Pd Nanocomposites Resulting from Combined Reactions Thermomechanical Processing
Authors: Cantando Elizabeth D. , Ludtka Gerard M. , Mackiewicz-Ludtka Gail , Soffa William A.
Published: July 2011

Hypostoichiometric Fe-Pd binary alloys (35-45 at% Pd) were severely deformed (>90%) and subsequently aged to induce concomitant recrystallization, precipitation, and ordering. This thermomechanical processing strategy was articulated by Hornbogen [1] over thirty years ago. The resulting exchange-coupled ferromagnets contain ferrite precipitates and a complex metastable two-phase lamellar transformation product comprised of ordered L10 and a metastable FCC phase. The later duplex microconstituent is suggested to form in conjunction with a so-called pseudospinodal reaction [2] involving emerging cubic and tetragonal phases, whereby phase separation and ordering result from continuous changes in composition and a reduction in symmetry, cubic to tetragonal. The deformation texture of the parent austenite is substantially retained in the transformation product, resulting in anisotropy of the magnetic properties as determined by magnetometry (VSM). This paper presents electron microscopy results elucidating the crystallography and morphology of the phase mixtures including HREM. Magnetic field annealing is also included as a branch of our thermomechanical processing strategy, and we discuss the influence of the external fields on recrystallization, precipitation, and ordering.
Rate-Dependent Damping Capacity of NiTi Shape Memory Alloy
Authors: He Yong Jun , Sun Qing Ping
Published: July 2011

High damping capacity is one of the prominent properties of NiTi shape memory alloy (SMA), having applications in many engineering devices to reduce unwanted vibrations. Recent experiments demonstrated that, the hysteresis loop of the stress-strain curve of a NiTi strip/wire under a tensile loading-unloading cycle changed non-monotonically with the loading rate, i.e., a maximum damping capacity was obtained at an intermediate strain rate (ε.critical). This rate dependence is due to the coupling between the temperature dependence of material’s transformation stresses, latent-heat release/absorption in the forward/reverse phase transition and the associated heat exchange between the specimen and the environment. In this paper, a simple analytical model was developed to quantify these thermo-mechanical coupling effects on the damping capacity of the NiTi strips/wires under the tensile loading-unloading cycle. We found that, besides the material thermal/mechanical properties and specimen geometry, environmental condition also affects the damping capacity; and the critical strain rate ε.critical for achieving a maximum damping capacity can be changed by varying the environmental condition. The theoretical predictions agree quantitatively with the experiments.
Ferrite Formation Above the Ae3 in a Medium-Carbon Steel
Authors: Jonas John J. , Basabe Vladimir V.
Published: July 2011

A 0.45% C steel was deformed in torsion over the temperature range 762-872°C in a 5%H2-Argas atmosphere. Strains of 0.25-3.0 were applied at a strain rate of ε. = 4 s-1. The experimental parameters were varied in order to study the effects of strain and temperature on the formation of ferrite by dynamic transformation (DT) at temperatures above the Ae3. The critical strain for ferrite formation by DT was about 0.2 and its volume fraction increased with strain. The average ferrite grain sizes were about 1 to 2 µm and were fairly independent of temperature. It was observed that the deformation-induced ferrite remained fairly stable during 800 s of isothermal holding. In general, the experiments showed that DT takes place at temperatures above the Ae3 and that the reverse static transformation is much slower than the forward dynamic transformation.
Precipitation Process in a Cu-Ni-Be Alloy
Authors: Watanabe Chihiro , Monzen Ryoichi
Published: July 2011

The precipitation process in an aged Cu-1.9wt%Ni-0.3wt%Be alloy has been examined by high-resolution transmission electron microscopy. The precipitation sequence found is: Guinier- Preston (G.P.) zones → γ'' → γ' → stable γ. The disk-shaped G.P. zones and the disk-shaped γ'', γ' and γ precipitated phases are composed of monolayers of Be atoms on {100}α of the Cu matrix and alternative Be and Ni matrix layers parallel to {100}α. The γ'' phases consisting of two to eight Be-layers has a body-centered tetragonal (bct) lattice with a=b=0.24 nm and c=0.28 nm. The γ' or γ phase is bct with a=b=0.24 nm and c=0.26 nm or a=b=0.26 nm and c=0.27 nm. The γ'', γ' or γ phase aligns with the matrix according to the Bain orientation relationship. The growth kinetics of disk-shaped γ precipitates on aging at 500°C has been also investigated. The {001}α habit planes of the γ precipitates migrate by a ledge mechanism. The average thickness of the γ disks increases with aging time t as t1/2. An analysis of experimental data using a kinetic model yields the diffusivity of solute in the Cu matrix, which is in agreement with the reported diffusivity of Ni in Cu.
Reactive Diffusion between Ti and Cu-9.3Sn-0.3Ti Alloy at Solid-State Temperatures
Authors: Kajihara Masanori , Nakamura Shingo
Published: July 2011

The reactive diffusion between Ti and a bronze was experimentally examined using sandwich diffusion couples consisting of Ti and a Cu-9.3Sn-0.3Ti alloy. The diffusion couples were isothermally annealed at temperatures of T = 923-1023 K. During annealing, CuTi, (Cu, Sn)4Ti3 and (Sn, Cu)5Ti6 compounds are formed as layers at the interface in the diffusion couple. The overall growth of the compound layers is controlled by volume diffusion at T = 1023 K but by boundary and volume diffusion at T = 923-973 K. Hence, the interface reaction is not the bottleneck for the growth of the compound layers under the present experimental conditions.
The Microstructure and Mechanical Properties of the Ni-Al-V Alloys Prepared by Levitation and Crystallization in Copper Mould
Authors: Czeppe Tomasz , Korznikova Galia F. , Świątek Zbigniew , Sypień Anna , Korznikov Alexander V. , Krajewski Witold K.
Published: July 2011

Microstructure and mechanical properties of NiAlV alloys of the composition belonging to the pseudo-binary Ni3Al-Ni3V cross-section were investigated. The samples were prepared by the cold crucible levitation melting (CCLM) and by re-melting and crystallizing in the small volume copper mould. The phase composition of the samples, with should result from the eutectoidal decomposition was not found. Instead the Ni3(Al,V) and Ni(Al,V) solid solution or seldom disordered solid solution were retained due to the relatively high cooling rates. In the compression test the NiAlV alloys crystallized in the copper mould revealed high ductility and strength.
Thermodynamic Prediction of Zr-Nb-O-H Phase Diagram Sections
Authors: Sopousek Jiri , Svobodová Marie
Published: July 2011

The paper deals with phase diagram calculations and predictions of selected binary, ternary, and Zr-Nb-O-H quaternary system. These systems are important as alloy base for cladding materials involving fissionable fuel in nuclear industry. The main attention is focused on the phase diagram prediction of Zr-1wt.%Nb-O alloy system at temperature conditions up to 2 000 °C. In addition, the influence of hydrogen content on the Zr-1wt.%Nb-O phase diagram is discussed. According to service conditions in nuclear industry, 1 000, 2 000 and 3 000 ppm of hydrogen contents are considered. The achieved results are presented as iso-concentration section of the phase diagrams. Impact on mechanical properties of the material under view is discussed.
Martensitic Transformation and Shape Memory Effect in Titanium-Gold Compound
Authors: Declairieux Charles , Vermaut Philippe , Portier Richard , Ochin Patrick , Denquin Anne
Published: July 2011

High temperature shape memory alloys offer numerous potential applications in industrial domains like aeronautics. Even if up to now, none of the studied alloys have found a place in airplane turbines, research in this field is still active. Starting from the well-known “room temperature” shape memory alloy NiTi, it has been demonstrated that the addition of a ternary element such as gold in substitution of nickel greatly enhances the temperatures of the martensitic transformation. In the binary TiAu compound, the martensite start temperature can attain 875 K with satisfying reversibility and cycling stability. From lattice parameters measurements, it has been shown that the maximum transformation strain can reach 10.75 % for Ti47Au53 alloy, which is comparable to that of the NiTi alloy. However, to the best of our knowledge, quantitative measurements of the recoverable strain by shape memory effect are not available in the literature. We present here some quantitative results of shape memory effect associated to this phase transformation in Titanium-Gold alloys measured after compression tests.
Laves Phase Formation in the Fe20Co18W Alloy Annealed at 800°C
Authors: Galimberti Paolo , Lay Sabine , Antoni-Zdziobek Annie
Published: July 2011

The precipitation behaviour of the Fe20Co18W (wt%) alloy was studied by transmission electron microscopy during aging treatments at 800°C. The decomposition of the matrix produces the C14 phase. At the beginning of the heat treatment, the observation at the atom scale indicates that the structure of the precipitates does not coincide exactly with the Laves phase. Using the orientation relationship between the Fe based matrix and the precipitates it is shown that simple atomic shifts can lead to the transformation from the bcc matrix to the C14 Laves phase.
Variant Selection in Austenitic Stainless Steel Samples after Cold Rolling and Tension Deformation
Authors: Abreu Hamilton F.G. , Morais Nathanael , Herculando Flavio , Da Silva Marcelo Gomes , Nascimento Alex
Published: July 2011

The deformation process can induce the precipitation of martensite in austenitic stainless steels. When shear stress is applied at temperatures near Ms, displacive transformation (martensitic transformation) mode is activated. When external stresses are applied, the work done contributes to a change in free energy either raising or lowering the Ms-temperature. Orientation relationships during austenite to martensite phase transformation were investigated in an austenitic stainless steel samples deformed by cold rolling and deformed in a tension test. EBSD (electron backscatter diffraction) and X-ray diffraction techniques were used to evaluate parent austenite texture and martensite texture after transformation. The observed orientation relationship between austenite and martensite was compared with the predicted orientation relationship by the phenomenological theory of martensite crystallography (PMTC). Aspects related to variant selection were discussed based on the criterion for the action of applied stress in the martensitic transformation postulated by Patel and Cohen. Results showed a very good agreement between measured and calculated results.
Model for the Annealing of Partial Martensite-Austenite Microstructures in Steels
Authors: Santofimia M. J. , Speer John G. , Zhao Lie , Sietsma Jilt
Published: July 2011

The microstructure formed in a steel after a partial martensitic transformation contains martensite-austenite assemblies with similar chemical composition in the two phases. In the absence of carbide precipitation, further annealing or tempering of this microstructure is believed to promote carbon partitioning from the martensite to the austenite. Experimental observations suggest that this carbon diffusion might take place in combination with migration of martensite-austenite interfaces. In this work, the effect of the martensite and austenite dimensions on the interaction between the carbon partitioning from martensite to austenite and the interface migration during annealing of martensite-austenite microstructures is analyzed. With that aim, simulations have been done by using a model in which the chemical potentials of carbon in martensite and austenite are assumed to be the same at the interface and motion of the phase interface is occurring when an appropriate driving force is present. Carbide precipitation is precluded in the model, and three different assumptions about interface mobility are considered, ranging from a completely immobile interface to the relatively high mobility of an incoherent ferrite–austenite interface.
Microstructures of Cu-Alloyed Ductile Cast Iron Treated by Two-Step Austempering
Authors: Kitkamthorn Usanee
Published: July 2011

The excellent mechanical properties of austempered ductile iron are due to the unique matrix microstructure called “ausferrite”. Such microstructure is obtained from the first stage reaction during isothermal transformation of austenite into ferrite and high carbon austenite. The second stage reaction is the decomposition of high carbon austenite into ferrite and carbide. In this study, the microstructure of Cu-alloyed ductile iron treated by two-step austempering was investigated using SEM and TEM. The two-step austempering consists of 1) quenching from 900°C to 300°C and hold for 6 minutes in a salt bath, and 2) increasing the temperature of the salt bath by 30°C at the rate of 3°C per minute and holding until the total time was 120 minutes. The SEM samples were prepared by grinding to 1200 grit, polishing with 0.3 micron alumina powder and etching using 2% nital. Thin foil discs of 3 mm diameter for TEM observation were prepared by mechanical thinning to 80-100 microns and were then dimpled to 20 microns. Final thinning was carried out using Gatan precision ion polishing system (PIPSTM). The thin foils were then examined using Jeol-JEM2010 operating at 200 kV. TEM results show that the matrix microstructure is ferrite subunits interspersed with retained austenite films. The subunits and austenite films exhibit either Kudjamov-Sachs (K-S) or Nishiyama-Wasserman (N-W) orientation relationships. Occasionally, fine carbide precipitate was observed.
Thermal Stability of Athermal and Deformation Martensite in Ni27Ti2AlMoNb Steel
Authors: Borowski Tomasz , Kowalczyk Maciej , Jeleńkowski Jerzy
Published: July 2011

The study was devoted to the thermal stability of the phases present in chromium-less and practically carbon-less Ni27Ti2AlMoNb steel. Steel with an austenitic structure was subjected to martensitic transformations using a thermal treatment, namely cooling to below the temperature Ms (beginning of the martensitic transformation), or by plastic deformation using the TRIP effect. The cooling in liquid nitrogen gave a martensitic-austenitic structure with athermal martensite α’a. The martensite had a lenticular morphology, and its volumetric share was 51%, which is typical of duplex type steels. The 50% squeeze of the austenitic steel resulted in the formation of deformation martensite α’d with a lamellar structure (this transformation is only possible below a certain temperature Md). During the experiments, the thermal stability of the two phases, α’a and α’d, at temperatures of 450°C and 550°C was examined. The changes taking place in the steel structure when the athermal martensite and deformation martensite were annealed below and above the temperature As (beginning of the austenitic transformation) were observed using a vibrating sample magnetometer and an optical microscope.
Mesoscopic TDGL Model for Formation of Domain Structures in D019 Type Ordering
Authors: Oguma Ryuichiro , Matsumura Syo , Eguchi Tetsuo
Published: July 2011

The present authors recently presented the time-dependent Ginzburg-Landau (TDGL) formulation for L12 type ordering processin binary alloys, taking into account the symmetrical relationships of these ordered phases. Extending the formulation, the authors have developed the TDGL model for microstructural evolution of D019 type ordering. The D019 structure based on hcp is divided into four equivalent sublattices. The site occupation probabilities are given as a function of three order parameters and a composition parameter. Multiple types of variants of the structures are represented by the order parameters. Mean-field free energies are defined in a form of Landau type expansion with the order parameters and the composition parameter. Interfacial energies due to local variations of degrees of order and composition are given in a gradient square approximation. Kinetic equations for time-evolution of the order parameters and the composition one are derived from the Ginzburg-Landau type potential consisting of the mean-field free energies and the interfacial energy terms. Three-dimensional numerical simulations based on the kinetic equations have been performed, and the domain structures obtained are compared with a TEM image of Cu3Sn alloy.
Theoretical and Experimental Evidences of Sequential Phase Formation during Sub-Nanometric-Thick Film Reactive Diffusion
Authors: Portavoce Alain , Tréglia Guy , Lalmi Boubekeur , Girardeaux Christophe , Mangelinck Dominique , Aufray Bernard , Bernardini Jean
Published: July 2011

Silicide sequential phase formation during tens-of-nanometer-thick metallic film reaction on Si substrate has been extensively studied. Nevertheless, the reasons of sequential phase formation are still under debate, and have been poorly studied at the atomic scale. Using atomistic kinetic Monte Carlo simulations, we show that considering a binary fcc non-regular solid solution, without diffusion asymmetries, the diffusive reaction of a sub-nanometer-thick film (~5 atomic monolayers) on a semi-infinite substrate leads to the sequential formation of all the phases present in the binary phase diagram, starting with the film atom richest phase. These predictions are supported by experimental observations: the dissolution of a 4 monolayer-thick Si film on a Ni(111) substrate, during in-situ ultra high vacuum Auger electron spectroscopy, shows delays and kinetic changes in the dissolution process that may correspond to the sequential formation of the Ni-Si compounds, i.e. NiSi2, NiSi, Ni3Si2, Ni2Si, Ni31Si12 and Ni3Si.
Simulation of the β→α(O) Phase Transformation due to Oxygen Diffusion during High Temperature Oxidation of Zirconium Alloys
Authors: Toffolon-Masclet Caroline , Desgranges Clara , Corvalan-Moya Carolina , Brachet Jean-Christophe
Published: July 2011

The EKINOX numerical code, formerly developed to simulate high temperature oxidation of Ni alloys, has been recently adapted to solve out the issue of high temperature oxidation of Zirconium alloys. This numerical code is a one dimensional model that simulates the growth of an oxide layer using a specific algorithm for moving boundaries problem. In order to simulate the oxygen diffusion inside Zr alloys, an adaptation of the EKINOX code was necessary. It consisted in adding, first, a non-null oxygen equilibrium concentration in the substrate and second, a new interface in order to simulate the β/α(O) phase transformation due to oxygen diffusion. In this study, EKINOX has also been coupled with the thermodynamic database for zirconium alloys ZIRCOBASE (thermocalc formalism) in order to obtain accurate concentrations values in each phases (considering local equilibrium at each interface). The present paper illustrates the simulation ability of the code by comparing experimental and calculated oxygen diffusion profiles corresponding to different cases, from isothermal oxidations at high temperature (900 < T < 1250°C) to the study of dissolution kinetics of a pre-transient oxide layer under a neutral environment. The influence of pre-hydriding from a few hundreds up to thousands weight-ppm is also derived from the calculations.
Kinetics and Formation Mechanisms of a Nanostructured Fe-Y2O3 Powder Prepared by Reactive Ball Milling
Authors: Couvrat Mathieu , Legendre Fabrice , Brocq Mathilde , Chaffron Laurent , Boulanger Loic , Bonnaillie Patrick
Published: July 2011

Reactive high energy ball-milling has known a growing interest from both fundamental and applied point of view. We focus here on the specific system Fe-Y2O3 metal-oxide nanocomposite because of its potential application to the synthesis of oxide dispersion strengthened steels, which are promising materials for nuclear applications. YFe3 and Fe2O3 were ball-milled during different milling durations in the stoichiometric proportions defined by the chemical reaction 2 YFe3 + Fe2O3 → 8 Fe + Y2O3. The obtained milled powder was characterized by XRD, SEM, TEM and their thermal behaviour was investigated by DTA. Through those characterizations, a Mechanically induced Self-propagating Reaction (MSR) was observed and several steps in the ball-milling process were identified: mixing of reactants, chemical reaction propagation, amorphization and refinement of the microstructure. The role of the milling intensity was also examined.
Precipitation in Solution-Treated Al-4wt%Cu under Cyclic Strain
Authors: Farrow Adam , Laird Campbell
Published: July 2011

Solution-treated Al-4wt%Cu was strain-cycled at ambient temperature and above and the precipitation behavior investigated by TEM. In the temperature range 100°C to 200°C precipitation of Θ´´ appears to have been suppressed and precipitation of Θ´ promoted via cyclic strain. Anomalously rapid growth of precipitates appears to have been facilitated by a vacancy super-saturation generated by dislocation motion, with a diminishing effect observed at higher temperatures due to the faster recovery of non-equilibrium vacancy concentrations. Θ´ precipitates generated under cyclic strain are considerably smaller and more finely dispersed than those typically produced via quench-aging due to their heterogeneous nucleation on dislocations, and possess a low aspect ratio and rounded edges of the broad faces due to the introduction of ledges into the growing precipitates by dislocation cutting. Frequency effects indicate that dislocation motion, rather than the extremely small precipitate size, is responsible for the observed reduction in aspect ratio. Accelerated formation of grain boundary precipitates appears partially responsible for rapid inter-granular fatigue failure following cycling at elevated temperatures, producing fatigue striations and ductile dimples coexistent on the fracture surface.
Transformation Kinetics and Resulting Microstructure in MMC Reinforced with TiC Particles
Authors: Mourot Mickael , Courleux Alice , Dehmas Moukrane , Aeby-Gautier Elisabeth , Geandier Guillaume , Dezellus Olivier , Viala Jean Claude , Martin Olivier , Karnatak Nikhil , Danoix Frederic
Published: July 2011

The phase transformation kinetics on cooling and resulting microstructures of steel-based matrix composites (MMC) reinforced with TiC particles by powder metallurgy were studied. In addition, the phase transformation kinetics of the MMC were compared to those of the same steel without TiC and consolidated in the same conditions. The presence of TiC particles strongly favors the diffusive transformations in the steel matrix of the MMC. Different complementary techniques (XRD, SEM, TEM/EDX, atom probe tomography, in situ synchrotron XRD) were performed to analyze the chemical reactivity between TiC particles and the steel powders occurring during consolidation process and further heat treatments. Composition changes in the TiC as well as in the matrix were characterized. The chemical composition after treatment in the TiC particles tends toward the thermodynamic calculations with ThermoCalc. The effect of changes in chemical composition and the role of TiC particles acting as new favorable nucleation sites are discussed in regards to the obtained results.
Oxygen, Hydrogen and Main Alloying Chemical Elements Partitioning Upon Alpha←→Beta Phase Transformation in Zirconium Alloys
Authors: Brachet Jean-Christophe , Toffolon-Masclet Caroline , Hamon Didier , Guilbert Thomas , Trego Gwenaël , Jourdan Julien , Stern Anthony , Raepsaet Caroline
Published: July 2011

Due to their adequate properties, zirconium alloys are the reference materials for the nuclear fuel cladding tubes of Light Water Reactors (LWR). During some hypothetical accidental High Temperature (HT) transients, the materials should experience heavy steam oxidation and deep metallurgical evolutions. This promotes Alpha-Beta phase transformations and an associated strong partitioning of oxygen/hydrogen and of the main chemical alloying elements (Nb, Sn, Fe and Cr). Moreover, it has been shown quite recently that such chemical elements partitioning during on-cooling Beta-to-Alpha transformation can strongly impact the residual mechanical properties of HT oxidized materials. Thus, it appeared that it was important to better quantify and, if possible, to compute the quite complex phase equilibrium that occurs in multi-alloyed zirconium materials in the presence of both oxygen and hydrogen. For that, systematic studies have been performed on industrial alloys, charged with oxygen and/or hydrogen. After applying different heating/cooling scenarii, both Electron Microprobe using Wave Dispersive Spectrometry (WDS) and Nuclear Microprobe using Elastic Recoil Detection Analysis (ERDA) have been applied. Finally, to support the observed chemical elements partitioning between the Alpha and Beta allotropic phases, some thermodynamic calculations have been performed thanks to the development and the use of a specific thermodynamic database for zirconium alloys called “Zircobase".
Modelling the in-Service Microstructural Evolution of Ni-Based Superalloys for Power Generation
Authors: Liu Tian Xiang , Gill Simon P.A. , Atkinson H.V.
Published: July 2011

High temperature operation of power plant increases their efficiency and reduces emissions. Low gamma-prime fraction nickel-based superalloys, such as IN617, are becoming increasingly important in substituting for conventional steel components due to their better performance at higher temperatures. The aim of this work is to model the microstructural evolution in this alloy under typical operating conditions and relate this to its creep response. Although classified as solid solution strengthened alloys, they contain a range of different precipitates which contribute to the creep resistance, the most influential of these being gamma prime. The model is developed in three stages. Firstly, a precipitate-level variational model is derived to describe the nucleation and growth of individual particles and their interactions. The results are then passed up to a grain-level simulation where the response of a statistically significant particle ensemble is simulated via the evolution of particle distributions. The resulting model incorporates the effects of heat treatment and stress to give the simultaneous size and number evolution of the different phases in the material. This information is then used to construct plastic strain-temperature-time diagrams in order to estimate the creep rupture life of the material.
Modeling High Strain Rate Viscoplastic Deformations Combined with Phase Changes
Authors: Montheillet Frank , Roy Gilles
Published: July 2011

Metallic materials submitted to high strain rates upon dynamic loading can undergo phase changes induced by strains, stresses, and/or temperature increase associated with self-heating. Various mechanical and metallurgical assumptions have been proposed and implemented in numerical codes to deal with such complex interactions. In order to assess their respective influences, a simple nearly analytical model was developed and applied to the classical sphere expansion test carried out on a two-phase strain hardening, strain rate and temperature sensitive material. In this paper, classical homogenization assumptions are compared for deriving the overall material flow stress. Strain hardening transfer upon phase transformation is accounted for. Finally, the respective weights of the various contributions to the work rate, associated with stored energy, self-heating, and phase change, are analyzed.
Phase Transformations in the Al-Si Coating during the Austenitization Step
Authors: Grigorieva Raisa , Drillet Pascal , Mataigne Jean Michel , Redjaïmia Abdelkrim
Published: July 2011

Nowadays more and more hot stamped steel sheets dedicated for the automotive body-in-white structure are pre-coated to prevent the steel surface against iron oxidation and decarburization during the austenitization step. For these applications, the coating is deposited by continuous hot-dipping the steel in an Al-Si bath. The Al-Si coating, at the delivery state, contains Al-grains, Al-Fe-Si ternary phases, Al-Fe binary phases. During the austenitization, the Al-Si coating transforms completely by inter-diffusion and solidification reactions. The mechanisms of Al-Fe-Si phase transformations at high temperature are almost unknown. The phase transformations occurring during austenitization define the final coating microstructure responsible for the in use properties of the product like spot welding, painting adherence or corrosion behavior. It is the aim of this paper to propose a new way of understanding the mechanisms of phase transformation in the Al-Si coating during the austenitization step (between 900 and 930°C) before the transfer into the hot-stamping press.
Dynamics of the Quenching and Partitioning (Q&P) Process
Authors: Bigg Timothy D. , Matlock David K. , Speer John G. , Edmonds David
Published: July 2011

The novel heat treatment concept of Quenching and Partitioning (Q&P) offers exciting prospects for the production of higher strength steel products with enhanced formability from a microstructure containing retained austenite and martensite. The Q&P process hinges on an interrupted quench and partitioning step at intermediate temperatures whereby the untransformed austenite can be thermodynamically stabilised by enrichment of carbon from the supersaturated martensite. Although the concept is similar to that producing carbide-free bainite in TRIP-assisted steel, Q&P offers the advantage of separating the ferrite formation and austenite enrichment stages of the process. While the concept is readily understood, the details of microstructural evolution during interrupted quenching and partitioning steps are difficult to study and are generally inferred from dilatometry or metallographic examination after a final quench back to room temperature. Consequently, in this study, alloying has been used to develop a model alloy in which the sequential steps of heat treatment can be separated for closer, more direct inspection by neutron diffraction techniques.
Precipitation Sequence and Kinetics in an Fe-Si-Ti Alloy
Authors: Perrier Malika , Deschamps Alexis , Donnadieu Patricia , de Geuser Frédéric , Danoix Frédéric , Bouaziz Olivier , Bréchet Yves
Published: July 2011

The Fe-Si-Ti system is known to show nanoscale precipitation of the Fe2SiTi Heusler phase with potentially high volume fraction (~4%), very high density and a size ranging from 1 to 20nm after artificial aging. The strong hardening potential of these precipitates make these steels candidates for automotive applications; however no understanding of the precipitation sequence (competition with other phases) nor the precipitation kinetics are available. The present study presents a quantitative study of the precipitation kinetics (size, volume fraction and number density) in a wide temperature range (450-800°C), realised by coupling systematically Small Angle Neutron Scattering (SANS), Transmission Electron microscopy (TEM) and Tomographic Atom Probe (TAP). Tensile tests were also carried out so as to determine the microstructure/properties relationships. Along the complete temperature range, it is shown that a compromise between time for precipitation and small precipitate sizes can be reached around 550°C. At this intermediate temperature, precipitation is shown to occur in two steps, linked with a second nucleation process after nucleation & growth of the first family of Fe2SiTi has been completed. This second precipitation step results in a temporary decrease in precipitate size and an increase in hardness. The nature of these precipitates is discussed in view of the TEM and TAP observations.
Modelling Age Hardening CuCr1Zr Electrode Alloy Softening during Resistance Spot Welding
Authors: Carron Denis , Gauthier Elise , Pouvreau Cedric , Rogeon Philippe , Pilvin Philippe , Soigneux Jacky , Lety Thomas
Published: July 2011

High strength zinc-coated steels are used for automotive applications when high corrosion resistance and weight reduction are required. Resistance spot welding is the main method to assembly auto body. Steel sheets are held together under pressure exerted by copper alloy electrodes which concentrate welding current and clamp the sheets together. But welding of high strength coated steels reduces the electrode life. Even if electrode deterioration is a well-known problem, the understanding and modelling of the complex deterioration modes at different regions of the electrode is still limited. Developing a comprehensive thermo-electrical-metallurgical-mechanical model that describes the sequential deterioration is thus lacking. This work is a preliminary study which specifically addresses microstructural evolution modelling in age hardened CuCr1Zr electrode alloy. Evolution of precipitation is simulated using two models: a Johnson-Mehl-Avrami-Kologoromov model and the Myhr and Grong model. In both cases a calibration procedure based on hardness data was involved. Short isothermal heat treatments were used to develop a ‘master curve’ which captures the precipitate evolution. Preliminary results about the comparison of the two models are presented.
Mathematical Modelling of NbC Particle Nucleation and Growth in an HSLA Steel under Elastic Deformation
Authors: Ouden Dennis , Vermolen Fred J. , Zhao Lie , Vuik Cees , Sietsma Jilt
Published: July 2011

This study attempts to incorporate the effect of elastic deformation in a previously proposedmodel for the nucleation and growth of precipitates. We adapt the KWN-model by Robson to incor-porate the effect of strain energy arising from elastic deformation on the homogeneous nucleation andgrowth of NbC particles in a High Strength Low Alloy (HSLA) steel at constant temperature. Simula-tions of the nucleation and growth of NbC particles in an HSLA steel on the cylindrical region showthat the incorporation of elastic strain energies has a noticeable impact on the process. The derivedquantities of homogeneous nucleation and growth, such as the particle number density and the meanparticle radius, show a clear spatial correlation with the calculated strain energy.
Restitution of the Shapes and Orientations of the Prior Austenitic Grains from Inherited Alpha' Orientation Maps in Steels
Authors: Gey Nathalie , Blaineau Pierre , Germain Lionel , Humbert Michel , Barbier David , Perlade Astrid
Published: July 2011

We propose to reconstruct the g orientation maps from the α maps inherited by the bainitic or martensitic γ→α phase transformation. Our approach comprises two main steps (1) identification of reliable fractions of parent grains – each γ fraction is determined from neighbouring variants related to a unique γ orientation with a low tolerance angle; (2) expansion of these fractions by collecting adjacent variants being in orientation relation (OR) with the calculated g orientation - using a higher tolerance around the strict OR. Moreover, this fully automated g map reconstruction is further improved by an additional semi-automated analysis of α/γ maps. This reconstruction procedure was applied to the α microtexture of bainitic steels. The reliability of the calculations was checked by comparing each γ grain orientation and their corresponding α variants. The results show that even with a large spread around OR, the shape and orientation of most of the γ grains are accurately calculated.
Hydrogen-Storage Properties of Nanocrystalline Mg-Based Materials Created through Controlled Devitrification of a Metallic Glass
Authors: Lass Eric A.
Published: July 2011

Mg-based nanostructured materials with a composition of Mg85Ni15-xMx (M=Y, La, or Pd) have been fabricated by proper alloying additions and controlling the crystallization process of melt spun metallic glass ribbon. XRD suggests that the average crystallite sizes range from 100 nm in the binary materials to <30 nm in the ternary alloys. Hydrogen absorption/desorption measurements show improved properties compared to nanocrystalline alloys fabricated using other processing strategies. Surface treatment of the binary and Pd-containing ribbons by ball milling or submersion in aqueous NH4+ allows the materials to be activated at 473 K, significantly lower than conventional Mg-based hydrogen storage materials. Y and La additions improve the maximum storage capacity. Absorption kinetics are also improved the materials is alloyed with La, while Y slows the reaction kinetics. Some degradation in storage capacity is observed when the materials are exposed to a cyclic absorption/desorption process, likely due to microstructural coarsening. The Mg85Ni10Pd5 composition fully absorbs and desorbs ≈5 wt. % H at 473 K, while other bulk Mg-based materials require temperatures in excess of 573 K.
The Role of Applied Strain on Crystallisation Kinetics of an Amorphous Zr-Based Bulk Metallic Glass
Authors: Widmann Heiko , Strangwood Martin
Published: July 2011

The crystallisation behaviour of Vitreloy 105 during different thermo-mechanical exposure conditions has been studied in a Gleeble 3500 thermo-mechanical simulator (TMS). Strains up to 0.1 applied at rates of 0.001 – 0.01 s-1 in the supercooled liquid region (SLR) from 420 – 435 °C resulted in no change in the crystallisation kinetics compared with purely thermal exposure for the same times and temperatures. Separate deformation studies on the amorphous bulk metallic glass confirmed that the deformation conditions used corresponded to Newtonian flow conditions. It remains to be confirmed whether the lack of influence of permanent deformation persists for deformation at higher strain rates in the non-Newtonian regime.
Ab Initio Calculations of Kinetic Properties in ZrC and TiC Carbides
Authors: Razumovskiy Vsevolod I. , Korzhavyi Pavel A. , Ruban Andrei V.
Published: July 2011

Self-diffusion of the metal and carbon atoms in TiC and ZrC carbides is studied by first principles methods. Our calculations yield point defects energies, vacancy jump barriers and diffusion pre-factors in TiC and ZrC. The results are in reasonable agreement with the available experimental data and suggest that the self-diffusion mechanism for metal atoms in these carbides may involve nearest-neighbor vacancy pairs (one metal and one carbon vacancy).
Microstructure and Properties of the Sintered Diamond Reinforced by Diamond-MWCNTs Composite Fibers
Authors: Deng Fu Ming , Lu Xue Jun , Liu Rui Ping , Xu Guo Jun , Chen Qi Wu , Li Wen Zhu
Published: July 2011

A new type of sintered diamond reinforced by diamond-MWCNTs composite fibers which were randomly orientated and even distributed in the diamond matrix was synthesized by using 3(wt)% mullti-walled carbon nanotubes(MWCNTs) as starting additive under high pressure of 5.8GPa at temperature of 1500°C for 1 min. A special polycrystalline diamond structure of direct bonding of both diamond to diamond and diamond to diamond-MWCNTs composite fiber was observed. The testing results show that it possesses not only high hardness (49-52GPa) and Young’s modulus (878GPa) but also high bending strength (1320~1540GPa) and fracture toughness (9.0~9.2MPa•M1/2) as it was theoretically predicted. The high performances of the composite were contributed to the fiber strengthening effect and the special structure which can offer more extensive diamond to diamond bonding.
Analysis of Effecting Factors on Surface Finish of Fused Silica Glass Grinding with Inclined Ball-Headed Diamond Wheel
Authors: Chen Ming Jun , Li Ziang , Luo Kang Jun , Liang Ying Chun , Fang Zhen , Yu Bo
Published: July 2011

Fused silica glass is widely used on the manufacture of optical apparatus and resonators due to it’s interesting optical and vibration properties. In order to machining the complex structures in the resonators and optical apparatus, grinding process with inclined ball-headed diamond wheel is discussed. Analytical model of the grinding process with inclined ball-headed diamond wheel was built firstly. Afterwards grinding experiments were conducted by varying the feed speed, the rotation speed, the cutting depth and the average grain size of the ball-headed diamond wheel. The machining surfaces were characterized by surface profiler to investigate the effect of the grinding parameters on the surface roughness. The measurement result shows the average grain size of the diamond wheel has important influence on the machining surface and the surface roughness at the groove bottom is better than the groove edge due to the wheel axis tilt angle.
An Adaptive Tool Path Generation for Large Scale Wedge/Aspheric Lens Element Grinding Based on Isophote Interpolation
Authors: Zhang Ning Ning , Jiang Chen , Wang Zhen Zhong , Guo Yin Biao
Published: July 2011

Large scale wedge/aspheric lens element is a combination of wedge prism and aspheric lens as a single piece component forming a decentred lens, which is primarily manufactured by Computerized Numerical Control (CNC) machining, especially 3-axis CNC grinding. This paper presents an efficient tool path generation approach based on isophote interpolation. The interpolation guarantees that interpolated points always stay on the iso-inclination curve of the parametric surface. This symmetry ensures that the method can improve and automate large scale wedge/aspheric lens element machining for 3-axis CAD/CAM systems. As part of the validation process, the tool paths generated are analyzed and compare with the desired part.
Study on Friction and Wear Properties of Self-Lubricating Impregnated Diamond Bit Cutters
Authors: Pan Bing Suo , Fang Xiao Hong , Niu Ming Yuan
Published: July 2011

To reduce the friction coefficient between impregnated diamond bit and rock, experiments on addition of graphite to the matrix material of bit cutters were conducted. The cutters were made up of diamond contained working layers and binding layers. The friction and wear properties of cutters and binding layers were investigated using a pin-on-disc friction & wear tester with granite as tribopair. The results showed that with addition of graphite, the hardness and friction coefficient of binding layer decreased, but its wear resistance increased; compared to cutters without graphite, those cutters containing graphite had lower wear loss and friction coefficient and their sliding wear process was much steadier, but diamond protrusion was still normal.
Sawing Characteristics of a Diamond Circular Blade with Grits in Ordered Distribution
Authors: Huang Guo Qin , Xu Xi Peng
Published: July 2011

The sawing characteristics of a diamond circular blade with grits set in ordered distribution were investigated in comparison with a conventional blade on which grits are of random distribution. The two blades were tested under the same sawing conditions. Forces and power were monitored during sawing. The results indicate that the changing tendency of sawing forces and power versus sawing parameters are basically same for the two blades. However, the setting of grits in ordered distribution leads to lower sawing forces as well as force ratio, and can reduce nearly one third energy consumption.
Experiment and Simulation on Residual Stress of Surface Hardened Layer in Grind-Hardening
Authors: Zhang Lei , Ge Pei Qi , Bi Wen Bo , Zhang Qian
Published: July 2011

The grinding heat is utilized to induce martensitic phase transformation and strengthen the surface layer of alloy steel by raising surface temperature higher than austenitic temperature and cooling quickly. The surface residual stress is an important factor to evaluate the quality of surface hardening layer effectively. The experimental values of residual stress in the surface hardened layer are achieved by using X-ray diffraction method and corrosion stripping method. The numerical values of residual stress are simulated by using re-meshing and finite element method. The simulation values trend of residual stress in surface hardened layer is consistent with experimental results.
The Designing and Wear Simulation of the Wheel Used in Super-High Speed Point Grinding
Authors: Gong Ya Dong , Liu Yue Ming , Han Ting Chao , Cheng Jun
Published: July 2011

The application of the wheel used in super-high speed point (SHSP) grinding is introduced in detail, depicting the applied rang of the wheel, through designing the wheel body and the layer of CBN in the wheel. The designed principle is inferred according to the specific shape, the grinding productivity is analyzed in the course grinding zone and the finished grinding zone, introducing the angle of course grinding zone, which affects the grinding parameters in SHSP grinding, the value of the angle is designed to be suited to the point grinding, and manufacturing the wheel, introducing the changed state of chip flowing grinding used in the new wheel, the micro-surface of the wheel is observed through microscope, whose the ratio of air hole and the layer of CBN are analyzed, simulating the wear trend of the new wheel, the conclusions about super hard abrasives and wearing are drawn at last, the application of SHSP grinding is related to designing and manufacturing of the wheel, which provides the equipment for realizing high precision and productivity processing and offers the referred basis for the theoretical research.
Radial Power Ultrasonic Vibration Honing Friction Analysis
Authors: Zhu X.J. , Wang Jian Qing , Cheng Quan , Wang Yan
Published: July 2011

Grinding chatter is a hazardous phenomenon that frequently occurred during grinding process. The topic takes radial ultrasonic vibration honing as an example to explore the dynamic changes of grinding force in ultrasonic honing process. By analyzing obtains the following conclusions: (1) The friction coefficient between work-piece and whetstone is a nonlinear time variable; (2) Adding radial ultrasonic is mainly to change the positive pressure between whetstone and work-piece, thereby affects the mutual friction between work-piece and oilstone in honing; (3) Whether ordinary honing or ultrasonic honing, friction dynamic changes along with time, performance of whetstone relative to work-piece is discontinuous sliding —jerking motion.