bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Finish Issues after Direct Metal Deposition
Authors: Peyre P. , Gharbi M. , Gorny C. , Carin Muriel , Morville S. , Carron Denis , Le Masson P. , Malot T. , Fabbro R.
Published: January 2012

Derived from laser cladding, the Direct Metal Deposition (DMD) laser process, is based upon a laser beam – projected powder interaction, and allows manufacturing complex 3D shapes much faster than conventional processes. However, the surface finish remains critical, and DMD parts usually necessitate post-machining steps. In this context, the focus of our work was: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish. Our experimental approach is based upon: (1) adequate modifications of the DMD conditions (gas shielding, laser conditions, coaxial or off-axis nozzles), (2) a characterization of laser-powder-melt-pool interactions using fast camera analysis, (3) a precise check of surface aspects using 3D profilometry, SEM, (4) preliminary thermo-convective simulations to understand melt-pool hydrodynamics. Most of the experimental tests were carried out on a Ti6Al4V titanium alloy, widely investigated already. Results confirm that surface degradation depends on two aspects: the sticking of non-melted or partially melted particles on the free surfaces, and the formation of menisci with more or less pronounced curvature radii. Among other aspects, a reduction of layer thickness and an increase of melt-pool volumes to favor re-melting processes are shown to have a beneficial effect on roughness parameters.
New Constitutive Analysis of Microstructural Evolution: Hot Compression of Gamma Iron
Authors: Saimoto Shigeo , Huang Ming Xin
Published: January 2012

Hot processing of austenitic steels is an essential step in the production of steel products. However its microstructural characterization is at best indirect and reliant only on the processing parameters. This work describes a novel method to use stress-strain data at various temperatures and strain rates to extract microstructural parameters. Two low-carbon steels with a magnitude difference in carbon content are compared.
Development of Innovative and Efficient Welding Technologies for Plates and Profiles Made of High Strength Steels Using the Example of the Production of Mobile Cranes
Authors: Scharff Arite
Published: January 2012

An investigation concerning laser beam – GMA – hybrid welding of high strength steels has been completed for a crane plant. Materials, welding procedure qualification tests and the course of action during welding a demonstrator were studied [1].
Model for Predicting Recrystallization Behavior of Cold Rolled Extralow Carbon Steel Sheets
Authors: Senuma Takehide , Takemoto Yoshito
Published: January 2012

Microstructual observations indicate that the recrystallization of cold rolled extralow carbon steel sheets occurs due to the abnormal growth of selected subgrains in recovered subgrain microstructures. The authors measured the orientations of a recovered microstructure of a cold rolled extralow carbon steel sheet by SEM-EBSP and classified the deformed grains into several types due to the orientation and its scattering degree. In this study, a model for predicting the recrystallization behavior of cold rolled extralow carbon steels has been developed by applying the model of Humphreys modified to the grain of each type.A good agreement between the experimental and calculated results using the model developed was obtained.
Evolution of Microstructure and Mechanical Properties during Tempering of Continuously Cooled Bainitic Steels
Authors: Sourmail Thomas , Smanio Véronique , Caballero Francisca G. , Cornide J. , Capdevilla C. , Garcia-Mateo Carlos
Published: January 2012

With the increasing demand for high performance engine or suspension components, bainitic steels are receiving interest as potential replacement of their quench and tempered counterparts. Indeed, for a number of mechanical components, ferrite pearlite microstructures are no longer sufficient in terms of mechanical properties. Bainitic steel grades allow production of hot-rolled bars or forged components exhibiting a homogeneous bainitic microstructure and achieving UTS up to 1200 MPa without the need for additional heat-treatments [1]. During tempering, these V-microalloyed bainitic steels exhibit unusual yield strength variations, with a very pronounced increase around 250-300 °C followed by the better known secondary hardening peak for temperatures around 600-650 °C. Indeed, after tempering at 250-300 °C, some of these steels exhibit an increase in yield strength of up to 200 MPa, concurrent with an increase in impact toughness of up to 25%. This, however, goes unnoticed if hardness measurements are used to characterize tempering. In the following, results are presented for three different bainitic steel grades, and the origins of the changes in mechanical properties are discussed.
Eutectoid Decomposition of δ-Ferrite in Ferritic-Austenitic Duplex Cast Steel - Structural and Morphological Study
Authors: Dyja D. , Stradomski Z. , Kolan Cezary , Stradomski Grzegorz
Published: January 2012

The influence of time and temperature of ageing on the σ-phase morphology in ferritic-austenitic cast steel have been investigated in this study. The morphology and quantity of the σ-phase were analyzed by using optical microscope, X-ray diffractometry, scanning electron microscope and image analysis, respectively. The annealing temperature has a significant influence on the morphology, volume fraction and the dynamics of σ-phase precipitation. Surface development of the σ-phase decreases from R=4.3, for the cast steel annealed at 700°C to R=2.4 for the cast steel annealed at 900°C, and the volume fraction Vvσ from 50.8% to 26.5%, respectively. The most rapid progress of δ → σ + γ’ transformation was observed at 800°C.
Precipitation Strengthening of Micro-Alloyed Steels Thermo-Mechanically Processed by Ultra Fast Cooling
Authors: Liu Zhen Yu , Tang Shuai , Cai Xiao Hui , Wang Guo Dong
Published: January 2012

Thermo-mechanical Controlled Processing (TMCP) is one of the greatest achievements in steel industry in the 20th century, which, however, depends too much upon low temperature rolling for the refinement of austenite grains, causing great loss in terms of productivity. To overcome this disadvantage, a new processing route with ultra fast cooling as the core has been proposed, and pilot rolling and industrial trials were carried out. As compared to conventional accelerated cooling, the ultra fast cooling can achieve cooling rate up to 300°C/s for 3 mm thick strip and highly homogeneous cooling by the pressurized water spraying. In the present work, the metallurgical backgrounds for ultra fast cooling in thermo-mechanical processing were studied and elucidated. By the pilot hot rolling experiments with a lean composition of a typical 600 MPa grade high strength steel, it has been found that the application of ultra fast cooling (UFC) at the exit of hot rolling mills can improve the strength by as much as 100 MPa as compared to the conventional TMCP. The strengthening mechanism lies in that the ultra fast cooling immediately after hot rolling may further improve the strengthening effects by precipitation, grain refinement, and dislocation hardening. The theoretical calculations and experiments indicate that the grain refinement, dislocation hardening, and precipitation in the TMCP with in-front UFC have caused the strength increments of 36, 34 and 54 MPa over the conventional TMCP with ACC, respectively. The microstructure characterization showed that the density of high angle grain boundaries had been increased, and the average size of precipitates had been reduced from about 34 nm to 10 nm with the cooling pattern changing from ACC to the application of UFC. The theoretical estimation indicates that when the cooling profile is changed from the conventional ACC to UFC+ACC, and to UFC, precipitation strengthening accounts for more and more strength increment in the improved strength of hot rolled micro-alloyed steels.
Kinetics of Grain Refinement by Warm Deformation of 304-Type Stainless Steel
Authors: Tikhonova Marina , Belyakov Andrey , Kaibyshev Rustam
Published: January 2012

The dynamic process of grain evolution in an S304H-type austenitic stainless steel was studied in multiple forging tests at temperatures of 500°C, 600°C and 700°C. The deformation microstructure with a grain size of about 100 to 400 nm resulted from continuous dynamic recrystallization. The size of new grains and the recrystallization kinetics decreased with decreasing the deformation temperature. The dynamically equilibrium grain size evolved at large strains followed a power law function of the flow stress with a grain size exponent of about-0.2. The formation of new fine grains was assisted by dynamic recovery, which leads to an apparent steady state flow at large total strains.
Effect of Bake-Hardening Treatment on the Mechanical Properties of High Strength Bainitic Steel Produced by Thermomechanical Processing
Authors: Timokhina Ilana B. , Beladi Hossein , Xiong Xiang Yuan , Hodgson Peter
Published: January 2012

The influence of pre-straining and bake-hardening on the mechanical properties of thermomechanically processed 0.2C-1.5Si-1.5Mn-0.2Mo-0.004Nb (wt%) steel was analysed using tensile test, transmission electron microscopy (TEM) and atom probe tomography (APT). This steel after processing had high strength (~1200MPa) and good ductility (~20%) due to the formation of fully bainitic microstructure with nanolayers of bainitic ferrite and retained austenite. The bake hardening (BH) of pre-strained (PS) samples increased the yield strength of steel up to 690MPa and showed the bake-hardening response of 220MPa due to the operation of several strengthening mechanisms such as transformation induced plasticity during pre-straining and pinning the dislocations by carbon during bake-hardening treatment. The carbon content of the bainitic ferrite and retained austenite before and after bake-hardening treatment, the solute distribution between these phases and the local composition of fine Fe-C clusters and particles formed during bake-hardening treatment was calculated using APT. The bainitic ferrite and retained austenite microstructural characteristics such as thickness of the layers and their dislocation density before and after bake-hardening treatment were studied using TEM.
Microstructure Control of a Low Carbon Martensitic Stainless Steel by Quenching and Partitioning Heat Treatment
Authors: Tsuchiyama Toshihiro , Tobata J. , Tao T. , Nakada Nobuo , Takaki Setsuo
Published: January 2012

Quenching and partitioning (Q&P) treatment was applied to a commercial low carbon martensitic stainless steel, AISI Type 410 (Fe-12Cr-0.1C). The condition of partial quenching and partitioning was optimized with consideration of the untransformed austenite fraction and stability of austenite (carbon concentration in solid solution). As a result, the amount of retained austenite could be increased up to approximately 15 vol%. Tensile testing revealed that the specimens after Q&P heat treatment exhibited lower yield stress and larger work hardening rate compared with quench-and-tempered (Q&T) specimens under the same tensile strength level, resulting in a significantly better strength-ductility balance. It was confirmed that the TRIP effect had contributed to the mechanical property.
Influence of Substitutional Atoms on the Solubility Limit of Carbon in B.c.c. Iron
Authors: Saitoh Hajime , Ushioda Kohsaku , Yoshinaga Naoki
Published: January 2012

No clear-cut information is available with regard to the effect of foreign atoms on the solubility limit of C in b.c.c. iron despite many previous studies. Against this backdrop, the influence of substitutional atoms (Mn, Cr, P, Si, Al) on the solubility limit of C in b.c.c. iron in equilibrium with cementite was investigated in low-carbon steels at a temperature of 700°C. In detail, the C solubility limit was determined from internal friction measurements combined with infrared analysis of C using a high-frequency combustion technique. It has been clarified that Mn, Cr, and Al hardly change the C solubility limit, whereas P and Si increase it. The thermodynamical calculation indicates that, under para equilibrium Si increases the C solubility limit and Mn hardly changes it, while under ortho equilibrium Mn and Si decrease it. However, the present experimental condition was verified to be close to ortho form. The discrepancy between the experiments and the calculations seems to come from the fact that: 1) single solute C atoms and the C atoms combined as Substitute-C complex are not distinguished experimentally, and 2) in the regular solution model, the non-uniform distribution of C atoms around alloying atoms is not introduced into the entropy term, which is something that should be studied further in the future.
On the Methodology of Thermal Desorption Spectroscopy to Evaluate Hydrogen Embrittlement
Authors: Pérez Escobar Diana , Verbeken Kim , Duprez Lode , Verhaege Marc
Published: January 2012

Thermal desorption spectroscopy (TDS) is a very important tool in hydrogen embrittlement (HE) related research and has been applied on many different materials over the last decades in order to improve knowledge on the HE phenomenon. TDS provides the opportunity to distinguish between different types of hydrogen traps based on the analysis of a spectrum with different peak temperatures each corresponding to hydrogen desorption from a specific trap. These peak temperatures, and consequently the different traps in a material, arise from the various microstructural characteristics of the material. However, TDS results are also influenced by many other parameters, such as the sample surface preparation, the electrolytes used for hydrogen charging, sample geometry, charging time, current density, charging temperature. Even though the use of thermal desorption to evaluate hydrogen-metal interactions has increased over the past years, a careful evaluation of the effect of these other parameters was not yet performed. In this work, the impact of some of the above mentioned parameters was studied. It was demonstrated that the sample geometry, the surface roughness, and the initial total pressure of the TDS chamber influenced significantly the obtained TDS spectrum.
Effect of Electric Current Direction on Texture Evolution in a Cold Rolled Fe-3%Si Steel under Electric Current Pulses Treatment
Authors: Wang Xin Li , Zhao Hong Ming , Dai Wen Bin , Zhao Xiang
Published: January 2012

The effect of electric current on the recrystallization texture evolution with the rolling direction both parallel and perpendicular to the current flow during electric current pulses (ECP) treatment was investigated. The results showed that the exerted current direction played a great role on the formation of recrystallization texture {111}<112> and Goss texture {011}<100> at the primary stage of recrytallization induced by ECP treatment. However, with the current density increasing, the effect of current direction on texture evolution almost could be ignored and the final texture components in the two cases all are Goss texture.
Effects of Magnetic Field Intensity on Carbon Diffusion in Pure Iron in the Single-Phase Austenite Region
Authors: Wu Yan , Lu Yan , Zhao Xiang , Zuo Liang
Published: January 2012

Effects of magnetic field intensity on carbon diffusion in pure iron in the single-phase austenite region were investigated. Specimens of high purity iron (99.99%) were buried in an air-proof melting pot filled up with cementation agent, and respectively subjected to isothermal annealing at 930° for 25 min with a heating rate of 5°C /min, and then cooled in the furnace. A magnetic field with different intensity was applied during the whole heating, isothermal holding and cooling processes. The results showed that the magnetic field annealing obviously hinders the carbon diffusion in the direction perpendicular to the magnetic field direction and this effect increased with the enhancement of magnetic filed intensity.
Improved Mechanical Properties in Ti/Mo-Bearing Martensitic Steel by Precipitation and Grain Refinement
Authors: Xu L. , Shi Jie , Cao Wen Quan , Wang Min Qing , Hui Wei Jun , Dong Han
Published: January 2012

The yield strength and impact energy properties for martensitic steel fabricated by vacuum induction melting, is investigated. It is found that the addition of Ti can improve the yield strength property of the martensitic steel after reheat quenching process, which can be attributed to increase in precipitation hardening from formation of TiC precipitates in the martensitic matrix and a superfine sized (~8μm) grains in the martensitic structure. Moreover, the yield strength can be further enhanced by Mo addition, which can be ascribed to a large amount of freshly nano-sized (1-10nm) precipitates in the final martensitic structure. The experimental and theoretical results on the contribution of TiC precipitates to hardening of the martensitic steel are in excellent agreement. In addition, the impact toughness also has been improved along with yield strength followed by the heat treatment, which can be attributed to the grain refinement and high ratio of high-angle grain boundaries after Mo addition.
Low Temperature Precipitation in Nb-Added Si- and Si-Free Bainitic Steels
Authors: Zuazo Ian , Cobo Sebastian
Published: January 2012

Precipitation strengthening by fine Nb-rich particles represents an important element on the design of low carbon high strength steels. This is typically obtained on steel strips by thermal holding at temperatures above 600°C following the austenite to ferrite transformation. These conditions are beneficial to obtain a large precipitation of small Nb-rich precipitates. On the other hand, precipitation at lower temperatures, in a phase already hard, such as bainite, has been scarcely studied. In this work, the precipitation phenomena occurring during isothermal treatments following the austenite to bainite transformation at 450°C are investigated. For this purpose, two Nb-alloyed low carbon steels with and without silicon are studied and the evolution of the microstructure is determined by the use of transmission electron microscopy and followed by hardness measurements. The presence of a hardness peak is not detected until long isothermal times (150h). Preliminary atom probe tomography (APT) characterization provides insight on the possible presence of fine NbC precipitates at the peak hardness treatment. A comparison with a Nb-free alloy indicates a significant hardening effect of niobium on the bainitic structure.
Characterization of Precipitation Kinetics of Inconel 718 Superalloy by the Stress Relaxation Technique
Authors: Calvo Jessica , Shu She Yu , Cabrera Jose María
Published: January 2012

Inconel 718 is a nickel-chromium-iron superalloy which presents excellent mechanical properties at high temperatures, as well as good corrosion resistance and weldability. These characteristics can be optimized with an appropriate control of microstructural features such as grain size and precipitation. Precipitates of different nature can form in these alloys, i.e. γ’’ (a metastable metallic compound Ni3Nb), γ’ (Ni3(Ti, Al), carbides and/or δ phase (intermetallic Ni3Nb). Aging treatments are usually designed to obtain the precipitation required in order to optimize mechanical properties. However, precipitation can also appear induced by deformation and therefore interfere with hot forming operations, such as forging. Under these conditions, precipitation may lead to an increase of the loads required to carry out the process. The aim of the work was the characterization of precipitation kinetics for Inconel 718. With this purpose, stress relaxation tests were carried out at temperatures ranging from 950°C to 800°C. Moreover, different amounts of deformation were applied to the samples, prior to stress relaxation, to evaluate the effect of this variable on inducing precipitation. Some samples were quenched at different relaxation times for metallographic evaluation. The results obtained through mechanical testing, together with a proper characterization of precipitation by Scanning Electron Microscopy, were the basis for obtaining precipitation-time-temperature (PTT) diagrams after different deformation conditions.
Shaping of Nanostructured Materials or Coatings through Spark Plasma Sintering
Authors: Estournès Claude , Oquab Djar , Selezneff Serge , Boidot Mathieu , Monceau Daniel , Grossin D. , Drouet Christophe , Chung U Chan , Roulland F. , Elissalde Cathy , Maglione M. , Chaim R. , Miele Philippe , Gurt-Santanach J. , Chevallier G. , Weibel A. , Peigney A. , Laurent Ch.
Published: January 2012

In the field of advanced ceramics, Spark Plasma Sintering (SPS) is known to be very efficient for superfast and full densification of ceramic nanopowders. This property is attributed to the simultaneous application of high density dc pulsed current and load, even though the sintering mechanisms involved remain unclear. In the first part of the paper, the mechanisms involved during SPS of two insulating oxide nanopowders (Al2O3 and Y2O3) are discussed while in the second part illustrations of the potential of SPS will be given for (i) Consolidation of mesoporous or unstable nanomaterials like SBA-15 or biomimetic apatite, respectively; (ii) Densification of core (BT or BST)/shell (SiO2 or Al2O3) nanoparticles with limited or controlled reaction at the interface. (iii) In-situ preparation of surface-tailored Fe–FeAl2O4–Al2O3 nanocomposites, and finally (iv) One-step preparation of multilayer materials like a complete thermal barrier system on single crystal Ni-based superalloy.
3D Imaging Using X-Ray Tomography and SEM Combined FIB to Study Non Isothermal Creep Damage of (111) Oriented Samples of γ / γ ' Nickel Base Single Crystal Superalloy MC2
Authors: Jouiad Mustapha , Ghighi J. , Cormier Jonathan , Ostoja-Kuczynski E. , Lubineau G. , Mendez J.
Published: January 2012

An unprecedented investigation consisting of the association of X-Ray tomography and Scanning Electron Microscopy combined with Focus Ion Beam (SEM-FIB) is conducted to perform a 3D reconstruction imaging. These techniques are applied to study the non-isothermal creep behavior of close (111) oriented samples of MC2 nickel base superalloys single crystal. The issue here is to develop a strategy to come out with the 3D rafting of γ’ particles and its interaction whether with dislocation structures or/and with the preexisting voids. This characterization is uncommonly performed away from the conventional studied orientation [001] in order to feed the viscoplastic modeling leading to its improvement by taking into account the crystal anisotropy. The creep tests were performed at two different conditions: classical isothermal tests at 1050°C under 140 MPa and a non isothermal creep test consisting of one overheating at 1200°C and 30 seconds dwell time during the isothermal creep life. The X-Ray tomography shows a great deformation heterogeneity that is pronounced for the non-isothermal tested samples. This deformation localization seems to be linked to the preexisting voids. Nevertheless, for both tested samples, the voids coalescence is the precursor of the observed damage leading to failure. SEM-FIB investigation by means of slice and view technique gives 3D views of the rafted γ’ particles and shows that γ corridors evolution seems to be the main creep rate controlling parameter.
Modeling the Electrical Response of Waspaloy due to the Nucleation, Growth, and Coarsening of γ′
Authors: Whelchel Ricky L. , Gerhardt Rosario A. , Littrell Ken C.
Published: January 2012

Waspaloy is a polycrystalline nickel-base superalloy used in disc rotors for gas turbine engines. Waspaloy, like other superalloys, is strengthened through the formation of the γ’ precipitate phase. As this precipitate phase evolves with processing and thermal exposure, it is desirable to non-destructively monitor the precipitate microstructural evolution. Electrical resistivity was used as such a non-destructive monitoring technique for aging temperatures ranging from 600°C to 800°C and aging times ranging between 2min and 263.5h. In the nucleation regime, a Johnson-Mehl-Avrami type equation was fit to the electrical response. For the growth and coarsening regimes, a volume distribution of precipitates was fit to the measured electrical resistivity. These fitting techniques were facilitated by microstructural data obtained from SEM imaging, X-ray diffraction, and small angle neutron scattering (SANS) measurements. For both cases, the models showed an excellent fit to the measured electrical data, implying that electrical resistivity is a viable technique for non-destructively monitoring the precipitate phase in Waspaloy.
Microstructure of Thermal Barrier Coatings (TBC's) Obtained by Using Plasma Spraying and VPA Methods
Authors: Góral Marek , Dudek Stanislaw , Filip Ryszard , Sieniawski Jan
Published: January 2012

Thermal Barrier Coatings are the main type of coatings used for protecting turbine blade surfaces and the surface of modern jet engines combustion chamber parts. Depending on the type of engine element, the coatings are produced as plasma-sprayed MeCrAlY bond-coats with a ceramic outer layer or as Pt-modified aluminide coatings with a ceramic EB-PVD-deposited layer. Currently, research is being conducted on the deposition of a new type of coatings consisting of bond-coats with mulitlayer structure. In the article, the results of the study on the obtainment of TBC's with multilayer structure are presented. To obtain the metallic bond-coat, the process of atmospheric plasma spraying and the out of pack aluminizing (VPA) method were combined. The coatings were deposited on the surface of Rene 80 nickel superalloy. The first layer of the coating was a plasma-sprayed MCrAlY bond-coat, on which a diffusion aluminide layer was deposited with out of pack method. On the bond-coat, a standard ceramic zirconium oxide (ZrO2*20Y2O3) layer was deposited. The microstructure analysis, was conducted, using light and SEM microscopy. The phase and chemical composition analyses were done using EDS and XRD methods.
Tensile Properties of Low Angle Boundaries of Single Crystal Superalloy DD6
Authors: Li Jia Rong , Shi Zhen Xue , Zhao Jin Qian , Liu Shi Zhong
Published: January 2012

The tensile properties of DD6 alloy with twist low angle boundaries were investigated at 760°C, 850°C and 980°C, and the misorientation angle of twist low angle boundaries of the specimens of the alloy varies from 0º to 12º. The results showed that when the angle of low angle boundaries is relatively small, it has a little effect on the tensile properties of the alloy. It is notable that effects of low angle boundaries on the tensile strength are weaker than those on the tensile elongation. The characteristic of quasi-cleavage, intergranular and dimple fracture were observed on the tensile rupture surfaces of the specimens, and the tensile fracture mechanism was discussed.
DTA Analysis on the Solidification Behavior of the Al2O2-Y2O3-ZrO2 Ternary Oxide System and Microstructural Investigation
Authors: Su Hai Jun , Zhang Jun , Guo Wei , Yu Jian Zheng , Liu Lin , Fu Heng Zhi
Published: January 2012

The well-aligned growth structures which derive from directional solidification of ceramic eutectics are of great interests due to their potential use in electronic devices and as structural materials at high temperatures. Because of the complexity of the component system and very high melting points, the solidification behavior on the oxide ceramic eutectic is still unclear up to date. In the presented paper, the Al2O3-Y2O3-ZrO2 ternary eutectic ceramic is remelted by a DTA apparatus. The maximal heating temperature is 1950 °C. The melting and solidification behavior are investigated by the DTA analysis. The solidification microstructure is investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). The results show that solidus temperature and the liquidus temperature are 1738.4 °C and 1750.1 °C, respectively. The formation path of eutectic phase is discussed. The microstructure of as-solidified eutectic ceramic shows a divorced ternary eutectic structure consisting of Al2O3, YAG and ZrO2 phases with a random distribution. Furthermore, the microstructural comparison with directionally solidified ternary eutectic ceramic is presented and discussed.
Precious Metals in High Temperature Applications - The Cause of Damage and its Avoidance
Authors: Merker Jürgen , Lupton David F. , Schölz F.
Published: January 2012

The broad application of platinum and platinum alloys results from their excellent high temperature mechanical properties as well as their near-perfect oxidation resistance and their outstanding resistance to corrosive attack by metal oxide melts such as fluxing agents. However, a few basic rules must be adhered to if platinum devices are to give satisfactory service. Platinum is susceptible to “platinum poisons” and other impurities. These “poisons”, the reasons for their corrosive effects, and techniques for minimizing or eliminating their influence are outlined.
Influence of Temperature and Strain Rate on Dynamic Softening Processes in Allvac® 718Plus™
Authors: Mitsche Stefan , Sommitsch Christof , Huber Daniel , Stockinger Martin , Poelt Peter
Published: January 2012

The efficiency of gas turbine engines can improved by an increase of the working temperature. As a consequence Allvac® 718Plus™ was developed to enhance the high temperature properties. Since the performance of this alloy is strongly related to the microstructure the knowledge of the softening processes is important to develop precise microstructure evolution models. Specimens were deformed at different temperatures (950°-1050°C) and strain rate (0.1s-1 – 10s-1) to strains of 0.2-1.5. The microstructures obtained were analyzed by electron backscatter diffraction (EBSD) in the scanning electron microscope to investigate the softening mechanisms at the respective forming conditions.
Oxidation Behaviors of Two and Three Phase Mo-Si-B Alloys via Si Pack Cementation
Authors: Song Young Ho , Park Joon Sik , Kim Jeong Min , Yi Seong Hoon
Published: January 2012

Mo-Si-B alloys have been received an attention due to the high temperature strength and phase stability. However, the nature of poor oxidation resistance often limits the application of the alloy system. In order to resolve the poor oxidation resistance of the alloy system, in this study, the oxidation behaviors of Si diffusion coated Mo-Si-B alloys have been investigated in order to identify the underlying mechanism for the effect of the constituent of the phase combination of Mo-Si-B alloys. The oxidation tests performed at 1100 °C show that the produced MoSi2 phase, as a result of the coatings, give an excellent oxidation resistance at prolonged high temperature exposure in air. The oxidation behaviors of uncoated and Si coated Mo-Si-B alloys have been discussed in terms of microstructural observations during oxidation tests.
A Brief Introduction to Alloy Phase Chemistry Determination under EPMA/SEM-EDS Conditions and its Applications
Authors: Peng Zhi Fang , Cai Li Sheng , Dang Ying Ying , Zhao Lei , Peng Fang Fang , Yang Zhi Gang , Yan Guang Zong , Chen Sheng Guang , Zhou Jun , Zhou Yuan Gui
Published: January 2012

A so called multiphase separation method (MPSM) is proposed to quantitatively separate precipitated phases from their surrounding matrix phase in chemistry for bulk alloy/steel samples under EPMA/SEM-EDS measurement conditions. Applied examples to comparisons of the results through the MPSM with the values either cited or obtained via other analytical means relevant are indicative of the feasibility, accuracy as well as applicability of the MPSM, which deal with chemistry, amount, lattice parameter, elemental partitioning, atomic-site occupancy and stability of precipitated phases of either superalloy or heat-resistant steel samples analyzed. Successful applications of the MPSM not only show a significant improvement for difficulties in accurate quantification in phase chemistry under the EPMA/SEM-EDS measurement conditions but also provide with a useful and helpful tool to determine some other important physical quantities in alloys and steels, which make it possible to quantitatively and more widely evaluate structure-property relationships of the materials investigated through analyzing their bulk samples under EPMA/SEM-EDS measurement conditions.
Effect of Surface Recrystallization on the Low Cycle Fatigue Behavior of Directionally Solidified Superalloy DZ4 by In Situ SEM Studies
Authors: Ma Xian Feng , Shi Hui Ji
Published: January 2012

The effect of recrystallization on the low cycle fatigue life of DZ4 directionally solidified superalloy was investigated for specimens with three different recrystallized layers, which were generated by shot peening (0.1MPa, 0.3MPa and 0.5MPa respectively) and a subsequent annealing heat treatment. The fatigue life showed a decrease for recrystallized specimens with shot-peening of 0.1 MPa and 0.3 MPa, and an unusual increase for that of 0.5MPa, in comparison with the original DZ4 specimen. In-situ SEM observations were performed on the short crack growth behaviors for both original and recrystallized specimens, which revealed the fracture mechanism and the interaction with microstructure. Quantitative analysis of fatigue crack growth rates rationalized the influence of recrystallization on the low-cycle fatigue life of DZ4.
High Temperature Characteristics of Unidirectionally Solidified Al2O3/GAP Eutectic Composites with a Novel Microstructure
Authors: Waku Yoshiharu , Ohtsubo Hideki , Nakagawa Narihito , Yasuda Hideyuki
Published: January 2012

Much attention has been paid to unidirectionally solidified ceramic composites as candidates for high-temperature structural materials. We have recently developed potential ceramic eutectics, which are named Melt Growth Composites (MGC). The Al2O3/GAP(GdAlO3) binary MGC has a novel microstructure, in which continuous networks of single-crystal Al2O3 phases and single-crystal GAP phases interpenetrate without grain boundaries. Chain structure in the Al2O3/GAP binary system is formed due to the frequent branching of both phases resulted in the entangled structure. Therefore, the Al2O3/GAP binary MGC has excellent high-temperature characteristics in the air atmosphere at very high temperatures. In the paper, high temperature strength, thermal stability of microstructure and strength, and fracture toughness of the Al2O3/GAP binary MGC are reported.
Microstructure and Mechanical Properties Development in Cross Roll Rolled Ni-30Cr Alloy
Authors: Song Kuk Hyun , Kim Han Sol , Kim Won Yong
Published: January 2012

In order to evaluate the microstructure and mechanical properties of cross roll rolled Ni-30Cr alloy, comparing with conventionally rolled material, this work was carried out. The materials were cold rolled to 90% in thickness reduction by conventional rolling and cross roll rolling methods and subsequently annealed at 700°C for 30 min. After this work, in order to evaluate the grain boundary character distributions of the materials, electron back-scattered diffraction technique was introduced. The application of cross roll rolling was more effective to develop the microstructure and mechanical properties than those of conventional rolling. As a result, the grain size was significantly refined to 1.3 μm in conventional rolling and 0.6 μm in cross roll rolling, compared to initial material (30 μm), respectively. Also, these grain refinements directly affected an increase in mechanical properties. In the present study, we systematically discussed the relationship between grain size and mechanical properties in terms of an increase in effective strain.
Microstructural Assessment of IN718: A Closed-Loop Fatigue Approach
Authors: Stoschka Michael , Maderbacher Hermann , Stockinger Martin
Published: January 2012

The goal of relating a local fatigue life approach with different microstructures requires the consideration of the main forging process dependent influence factors and their effect on grain size, grain shape, grain contiguity and others. The presented methodology shows the generation and use of a microstructural based evaluation method to link the grain-shape based texture and morphology to the low-cycle-fatigue behavior of superalloy 718. The developed microstructural based energy approach supports an alternative description of the microstructure and grain shape texture. Both, the morphology and the statistical distribution, although covering as-large-as grains, are assessed by two independent numerical parameters. A parametric link to local fatigue parameters was established using this alternative microstructural characterization technique. A prediction of the microstructural evolution during the forging process is already available at design stage for hot-forging of this nickel-base superalloy. In this regard the value of the first parameter e correlates with the mean grain size; the value of the second parameter b is affected by the local forging process history. This enables the lifetime assessment of local forging process at design stage using advanced forging simulation tools. This holistic approach of establishment an experimental based methodology from specimen tests, extensive companying metallographic evaluations, linking them with local forging parameters, implementing the supported microstructural parameters to forging simulation codes and calculating the local component lifetime closes the simulation chain for superalloy 718.
Solidification Structure of Incoloy800 Superalloy with Electromagnetic Field
Authors: Wang En Gang , Jiang En , Zhan Guo Feng , Deng An Yuan , He Ji Cheng
Published: January 2012

The evolution of solidification structure in Incoloy800 with and without electromagnetic stirring (EMS) are studied to investigate its influence on the morphology of solidifying crystals and element segregation. The samples examination and EDX analysis show that some broken dendrite in the subsurface of the ingot were brought into the internal part of the ingot, it is proves the shear mechanism of EMS to dendrite or column crystal in the initial solidifying period, and the equiaxed grain region is formed in the internal part of ingots owing to the stirring effect of EMS. Both of them are helpful to reduce the element segregation in Incoly800 ingots.
Modern Control Theory Applied to Remelting of Superalloys
Authors: Williamson Rodney L. , Beaman Joseph J.
Published: January 2012

Over the past several years we have worked to develop tools to improve the quality of superalloy ingots produced by vacuum arc remelting (VAR) and electroslag remelting (ESR). Part of this work has focused on developing model-based process controllers that employ predictive, dynamic, low-order electrode melting and ingot solidification models to estimate important process variables. These estimated variables (some of which are not subject to measurement) are used for feedback and to evaluate the health of the processes. Modern controllers are capable of detecting and flagging various process upsets and sensor failures, and can take remedial action under some circumstances. Model-based variable estimates are continuously compared with measurements when available, and the residuals are used to correct the next generation of estimates. This technology has led to improved VAR and ESR melt rate controllers and is currently being used to develop a VAR ingot solidification controller. A first generation ingot pool depth controller has been tested on a laboratory VAR furnace and the results are very encouraging. In this test, a 152 mm diameter Alloy 718 electrode was remelted into a 216 mm diameter ingot, but the technology is easily scaled to industrial sizes. Successful development of this technology could allow for melting at higher powers without the formation of channel segregates (freckles) by stabilizing the ingot solidification zone. It may also allow for the production of larger diameter VAR superalloy ingots than is possible to produce with the current generation of VAR controllers for the same reason.
Surface Recrystallization and Twin Formation in a Single Crystal Superalloy
Authors: Xiong J.C. , Li Jia Rong , Luo Y.S. , Liu Shi Zhong
Published: January 2012

The samples of single crystal superalloy DD6 were grit blasted and then heat treated in the temperature range of 1100-1250°C for 4h and the DD6 alloy ‘standard heat treatment’ in vacuum furnace, respectively. The results showed that cellular recrystallization occurred in the surface layer after heating at 1100°C for 4 hours. While equiaxed recrystallization grains occurred near the surface of the samples annealed at 1200°C for 4 hours, meanwhile, cellular recrystallization located between equiaxed recrystallization grains and the original region. With the improvement of the heating temperature, the size of cellular recrystallization decreased, while the size of equiaxed recrystallization grains increased, and the shape of the coarse γ′ phase in the cellular recrystallization changed from lamellar to equiaxial. Fully equiaxed recrystallization grains nucleated after standard heat treatment. Furthermore, the twins occurred in fully equiaxed recrystallization grains, and that the γ′ phase of the twin plane appeared different from that of the equiaxed recrystallization boundary. On the contrary, the twin formation was not observed in the cellular recrystallization grains. Therefore, the differences in twin behavior between the fully equiaxed recrystallization and cellular recrystallization grains were discussed.
Microstructure Change of B2 Precipitates in an Fe-Al-Ni Alloy due to Two-Step Heat-Treatment
Authors: Yamanaka Junji , Yamamoto Chiaya , Kuno Yasuhiro , Doi Minoru
Published: January 2012

We have been studying the microstructure change of B2 cubic precipitates into an A2+B2 complex structure in Fe-Al-Ni alloy. In this study, we carried out detailed observation using focused ion beam (FIB) and scanning transmission electron microscopy (STEM). First, Fe-14.3at%Al-10.3at%Ni solid solution was prepared. Secondly, the specimens were heated at 1173 K, at which they formed B2 cubic precipitates (ordered bcc) dispersed in an A2 matrix (disordered bcc). After that, the B2/A2 two-phase specimen was annealed at 973 K. Then we fabricated STEM specimens using FIB, followed by high-resolution secondary electron imaging. We repeated this slice-and-observation procedure to determine the detailed microstructure of this heat-treated alloy. At the early stage of the 973 K annealing, the A2 phase appeared in the original B2 precipitates and showed a spongelike structure, whereas small nanometer-order B2 particles appeared in the A2 matrix. The A2/B2 interface at this stage showed no anisotropic morphology. Therefore, the main driving force of this process may not be strain energy, but chemical and interface energies. Further annealing at 973 K decreased the number of small B2 particles in the A2 matrix, and these particles dissolved into the matrix eventually. The annealing also changed the A2/B2 spongelike structure, which was observed in the original B2 precipitates, into simple structures such as the A2 core and B2 crust. Then the B2 phase showed ordinal coarsening behavior. When B2 precipitates, which had hollow cubic morphology, were observed to be very close to each other, the face-centered area of the B2 crust tended to dissolve and only large B2 precipitates remained.
Recrystallization in HR3C Austenitic Heat Resistant Steel
Authors: Yin Feng Shi , Tian Li Qian , Xue Bing , Jiang Xue Bo , Zhou Li
Published: January 2012

In the present study, the recrystallization and grain growth behavior of HR3C austenitic heat resistant steel were studied by scanning electron microscopy and electron backscatter diffraction (SEM/EBSD). The HR3C steel was forged into a plate of 12mm in thickness and then solution treated at 1150-1250°C followed by an annealing treatment at 650-1050°C for 1h. The results show that the recrystalization occurs during the annealing treatment when the steel is solution-treated at 1150°C. Increasing the solution temperature to 1200°C or above, the recrystalization will not occur during the same annealing treatment. EBSD measured results show that the solution temperature has a significant effect on grain boundary character, especially on density of the low angle grain boundaries within the austenitic grain. The mechanism of the recrystallization and effect of annealing treatment on precipitation behavior of second phase were analyzed.
Foresight of Material Surface Engineering as a Tool Building a Knowledge-Based Economy
Authors: Dobrzańska-Danikiewicz Anna Danuta
Published: January 2012

Throughout history, a substantial or often leap technological progress, was determined by the availability of new engineering materials, which usually stimulated the improvement in the quality of life. The development of engineering materials constitutes one of the most significant elements in the field of science and technology, and innovative policy in Poland and Europe as regards the knowledge-based economy (KBE). The enhancement of the product functional properties, required by the new strategies of engineering materials development, as well as materials processing technologies is frequently connected with appropriate formation of the engineering materials surface layer structure and properties. Functional properties of many products depend not only on the possibility of transferring the mechanical load across the whole element section or its physicochemical properties, but, most often, they depend mainly on the surface layer structure and properties. The application of foresight methodology in the assessment of the state and prospects regarding the development of technology related to the formation of the materials surface structure and properties provides the possibility to manage knowledge in this field. It can be achieved through a formalization of the explicit and tacit knowledge gathering and use in order to increase production competitiveness, effectiveness, and innovation, improve the quality of life and achieve sustainable development. The objectives accomplished in such a way contribute to the increase in intellectual capital by enhancing the effectiveness of using the existing knowledge, creating new knowledge, as well as increasing the level of understanding and disseminating knowledge. The implemented foresight project will result in identifying the priority innovative technologies and strategic research trends in the scope of surface structure and properties formation of engineering materials and biomaterials whose development in the country will be of key importance within next 20 years.
Study on Surface Roughness Transformation during Metal Rolling
Authors: Almotairy Saud , Wei Dong Bin , Jiang Zheng Yi
Published: January 2012

Increasing the demand for cold rolled ultra thin strip as feedstock for miniaturized products has encouraged researchers to investigate the ways to increase the quality of such products, especially those related to strip surface roughness. Surface is known as quality factor in most of manufacturing processes. In this paper, the effect of the rolling parameters on the surface roughness transformation during metal rolling has been studied. The experimental results demonstrate that the surface roughness transformation during the metal rolling is highly affected by the designation of the processing parameters such as finishing temperature, reduction, rolling passes and lubrication. The results have been discussed to verify the validity of the new findings.