bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Properties of the Ternary L12 Compound Co3(Al,W) in Single and Polycrystalline Forms
Authors: Inui Haruyuki , Oohashi Takashi , Okamoto Norihiko L. , Kishida Kyosuke , Tanaka Katsushi
Published: July 2011

The mechanical properties of Co3(Al,W) with the L12 structure have been investigated both in single and polycrystalline forms. The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of Co3(Al,W) experimentally determined by resonance ultrasound spectroscopy at liquid helium temperature are 15~25% larger than those of Ni3(Al,Ta) but are considerably smaller than those previously calculated. When judged from the values of Poisson’s ratio, Cauchy pressure and ratio of shear modulus to bulk modulus (Gh/Bh), the ductility of Co3(Al,W) is expected to be sufficiently high. In the yield stress-temperature curve, a rapid decrease and an anomalous increase in yield stress is observed in the low and intermediate (1000-1100 K) temperature ranges, respectively. The former is concluded to be due to the solid-solution hardening effect while the latter is attributed to thermally activated cross-slip of APB-coupled a/2<110> superpartial dislocations from octahedral to cube slip planes.
Influence of Crystal Orientation on the Freckle Formation in Directionally Solidified Superalloys
Authors: Ma De Xin , Mathes Michael , Zhou Bin , Bührig-Polaczek Andreas
Published: July 2011

Freckle occurrence is known to be dependent on the casting size and the superalloy components with large cross section are more prone to freckle formation. In our directional solidification experiment of superalloys freckles are observed in some thin samples, while some significantly thicker samples in the same shell mould cluster remain freckle free. The EBSD analysis shows that the samples with freckles have a good <001> axial orientation, while in freckle free samples the primary dendrite stems diverge from the sample axis. In an analogue system the flow behaviour through a mushy zone was simulated, in which the dendrite network was placed in different orientation. The <001> dendrite array shows the lowest resistance to the vertical melt flow. As the dendrite alignment diverges from <001> orientation, the flow speed slows down and reaches the minimum at the <111> orientation. This orientation effect of the interdendritic permeability explains well why the crystal orientation plays such an important role in the occurrence of freckles in superalloy castings.
The Microstructure Changes in IN713LC during the Creep Exposure
Authors: Hutařová Simona , Kianicová Marta , Vlasák Tomás , Hutař Pavel , Podrábský Tomáš , Hakl Jan
Published: July 2011

Nickel-based creep resisting alloys (strengthened by γ´) are the basic materials for high-temperature constructional parts in aircraft engines and energy units. These parts are exposed to combined effects of mechanical stresses, high temperature and dioxide-corrosion conditions. The microstructure changes of cast polycrystalline Ni-based superalloy IN713LC after creep exposure were studied. Three specimens with three different diameters were used for creep tests. The degradation stage (damage parameter π) was determined for all parts of specimens. Individual parts of specimens were metallographic observed and analyzed by image analysis after rupture. The results were compared with model of stress distribution in the specimen with potential damage in the centre of the specimen.
Change in Microstructure at Grain Boundaries with Creep Deformation of Polycrystalline Nickel-Based Superalloy IN-100 at 1273K
Authors: Miura N. , Kondo Y. , Kubushiro Keiji , Takahashi Satoshi
Published: July 2011

The changes in the morphology of ’ precipitates and the dislocation substructures at the vicinity of grain boundaries with creep deformation were investigated on a polycrystalline nickel-based superalloy, IN-100. The experiments were done at 1273K in the stress range of 70-180MPa with one set of samples deformed until rupture and another interrupted after reaching the minimum creep rate. The cuboidal ’ precipitates were regularly arrayed at the vicinity of grain boundaries and eutectic ’ precipitates and carbides were observed at the grain boundaries on as-heat treated IN-100. However, on both the creep interrupted and ruptured samples at all stress conditions, plate - like shaped ’ precipitates covered the grain boundaries. The width of the plate - like shaped ’ precipitates increased with decreasing the stress and is wider in the creep ruptured than in the creep ruptured samples. There were few dislocations in the grains and in the plate - like shaped ’ precipitates, but a large number of the dislocations were observed around the interface of the plate - like shaped ’ precipitates. TEM observations on the specimen creep ruptured at 180MPa indicated that strong constant was observed at the vicinity of grain boundaries, but weak contrast in the grain interior. These results suggested that drastic plastic deformation occurred only at the vicinity of grain boundaries. Consequently, the plate - like shaped ’ precipitates at the grain boundaries inhibited the dislocations movement and acted as the creep strengthener.
Change in Gamma Prime Morphology and Dislocation Substructures of Single Crystal Nickel-Based Superalloy, CMSX-4, Pre-Crept at 1273K-400MPa with Simple Aging
Authors: Kondo Y. , Miura N.
Published: July 2011

The single crystal nickel-based superalloy, CMSX-4, creep interrupted at the creep strain of 0.01 at 1273K-400MPa was aged at 1273K without stress to make clear the /' rafting mechanism. And the changes in the ' morphology and the dislocation substructures at the /' interface with simple aging time were studied and compared with the previous work at 1273K-250MPa. The cuboidal ' precipitates were regularly arrayed when the creep test was interrupted, but changed to the rafted /' structures normal to the pre-creep stress axis with simple aging time. The aspect ratio of the ' precipitates increased with increasing simple aging time up to 3.60x106s, attained to the maximum value and then decreased. The maximum value of the aspect ratio at 400MPa was lower than one at 250MPa. A number of dislocations were tangled with each other at the /' interfaces of the creep interrupted specimen. These tangled dislocations were only rearranged by simple aging and the dislocation density at the /' interfaces was almost constant, independent of simple aging time. All dislocations of the creep interrupted specimen at the /' interfaces with six kinds of the <110> Burgers vectors were detected equally. The proportion of the six kinds of the <110> Burgers vectors didn’t change with simple aging time. Consequently, dislocations at the /' interfaces were considered as not the misfit ones, but the traces of mobile dislocations in the  channels and the formation of the rafted /' structures might be closely correlated with the rearrangement of tangled dislocations at the /' interfaces.
Effect of Thermophysical Properties and Processing Conditions on Primary Dendrite Arm Spacing of Nickel-Base Superalloys – Numerical Approach
Authors: Franke Martin M. , Hilbinger Michael , Heckl Astrid , Singer Robert F.
Published: July 2011

This paper presents the results of an investigation on the interrelationship between thermophysical properties, processing conditions and primary dendrite arm spacing for a nickel-base superalloy. The research was realized for CMSX-4, directionally solidified in a Bridgman furnace. For a systematic, fast and cost-efficient investigation numerical finite element models were applied. The numerical model, composed of thermophysical material data, geometric data and boundary conditions, was calibrated and experimentally validated. Microstructural parameters of the castings were determined for a broad range of processing conditions and varying thermophysical properties in order to study general influences. Withdrawal speed, furnace temperature, enthalpy of fusion, solidification range, heat conductivity and specific heat were varied accordingly. The primary dendrite arm spacing is predominantly influenced by withdrawal speed and furnace temperature, but shows only a weak dependency on thermophysical properties.
Liftime Optimization of Hot Forged Aerospace Components by Linking Microstructural Evolution and Fatigue Behaviour
Authors: Maderbacher Hermann , Gänser H.P. , Riedler Martin , Stoschka Michael , Stockinger Martin , Eichlseder Wilfried
Published: July 2011

Heavy-duty aerospace components are frequently hot forged to satisfy the high requirements concerning their mechanical behaviour. Only the usage of high-performance materials together with a near-optimum manufacturing process enables the production of parts that are at the same time lightweight and mechanically extremely durable. Not only the static properties, but also the fatigue behaviour of Inconel718 is strongly influenced by the material’s microstructure resulting from the forging and heat treatment processes. Therefore, the static and fatigue properties may be controlled via the microstructural properties by suitably adjusting the parameters of the manufacturing processes. The present work links the complete forging and heat treatment process to the local distribution of the material’s fatigue strength within a component; the effect of the operating temperature is also considered. To this purpose, an empirical model is derived from fatigue tests on specimens with different microstructures at different temperatures. The resulting fatigue strength model is implemented, along with a microstructural evolution model from earlier work [1], into a finite element code in order to predict the local fatigue strength distribution in a component after being subjected to an arbitrary forging process. In a further step, the finite element code is linked to an optimization tool for determining the optimum set of manufacturing process parameters such that the component lifetime is maximized while taking process constraints into consideration.
Comparison between Microstructure Evolution in IN718 and ATI Allvac® 718PlusTM – Simulation and Trial Forgings
Authors: Huber Daniel , Sommitsch Christof , Stockinger Martin
Published: July 2011

Aerospace gas turbine disks operate in an environment of relatively high stresses caused by centrifugal forces and elevated temperatures. Because of the strong mechanical requirements and narrow specifications of such parts not only a correct, defect free final geometry is necessary, but also a defined microstructure. Even though the microstructure evolution during thermo-mechanical processing is well studied and understood for superalloys like IN718, the influences cannot easily be described analytically. Thus simulation tools are used to assure process stability and to optimize design parameters to meet the tough requirements in aerospace industries. Microstructure simulation of IN718 (and other materials) is well established at Bohler Schmiedetechnik GmbH & Co KG and appreciated by its customers. The advent of the newly developed nickel-base superalloy ATI Allvac® 718PlusTM led to extensive investigations and the development of an adapted microstructure model by Bohler Schmiedetechnik GmbH & Co KG and its research partners. Aim of this paper is a comparison of the microstructure evolution in IN718 and ATI Allvac® 718PlusTM during the thermo-mechanical treatment of turbine disks. Influences of process temperature, strain and strain rate on the final grain size are discussed by finite element simulations with a coupled grain structure model. Experimental results from trial forgings are compared with the outcome of the microstructure simulations.
Microstructure Prediction during Incremental Processes for Hot Forming of 718 Alloy
Authors: Dumont Christian , Georges Eric
Published: July 2011

Main works on microstructure prediction on superalloys during hot forming processes deal with close die forging of 718 alloy. In this paper, we focused our interest towards incremental hot forming process. In that case, matters become more complex, due to the partially recrystallized microstructure we have to take into account at the beginning of each pass. An original method is presented in this paper, still using a phenomenological approach, according to Avrami formulation, with two main additional assumptions, in order to carry out computation on microstructure evolution during the process. Examples with comparisons between real and computed microstructure (recristallyzed fraction, different populations of grain size) enable us to valid our model for bar forging.
Application of Thermodynamic and Kinetic Modeling to Diffusion Simulations in Nickel-Base Superalloy Systems
Authors: Engström Anders , Bratberg Johan , Cheng Qing , Höglund Lars , Mason Paul
Published: July 2011

This paper presents a brief review, followed by some new results from recent diffusion simulations in Ni-base superalloy systems, performed by means of a thermodynamic and kinetic modeling approach as taken in the commercial finite-difference code DICTRA. The DICTRA code solves the multi-component diffusion equations, combining assessed thermodynamic and kinetic data in order to determine the full composition dependent interdiffusion matrix. The link between fundamental physics based models and critically assessed data allows simulations to be performed with realistic conditions on alloys of practical importance. Emphasis in this paper is on modeling and simulation of interdiffusion occurring between NiAl coatings and Ni-base superalloy substrates. For this purpose we have used the so-called homogenization approach to diffusion in multi-phase systems, recently implemented into the DICTRA software. The simulation results have been validated against experimental data and the agreement is very satisfactory given the complexity of the problem.
Viscoplastic Phase Field Simulation of Microstructural Evolutions under Complex Loadings in Ni-Base Superalloys
Authors: Gaubert Anaïs , Le Bouar Yann , FINEL Alphonse
Published: July 2011

An elasto-viscoplastic phase field model is proposed to study the microstructural evolutions under mechanical loadings in a Ni-base superalloy single crystal. Elastic anisotropy and inhomogeneity, as well as the description of the long range order in the γ’ phase are included in the model. Plastic activity is introduced using a continuum crystal plasticity framework. The coupled model is used to study microstructural evolutions in superalloys under creep at high temperature. Two loading orientations are investigated, [001] and [011]. Moreover simulations under alternate fatigue loading in the [001] orientation are performed. The viscoplasticity simulations are compared to purely elastic phase field simulations and experiments in order to show the influence of plastic activity on microstructural evolutions.
Microstructural and Mechanical Effects of Thermo-Mechanical Processing on ATI 718Plus® Contoured Rings
Authors: Covarrubias Octavio
Published: July 2011

ATI 718Plus® is a nickel-base superalloy designed to promote resistance and thermal stability at elevated temperatures. Beside these properties, this material presents superior formability during forging operations, making ATI 718Plus® a suitable material for the manufacture of non-rotating and rotating components for jet engine and land-based turbines. Present contribution summarizes main results when several contoured rings were produced by ring-rolling processes considering selected parameters as temperature and deformation ratio. Effect of solution and precipitation heat treatments on ATI 718Plus® microstructure and mechanical properties are also reported. These results include tensile testing at elevated temperature and stress-rupture testing. Microstructural evaluations performed by optical microscopy and electronic microscopy, complement reported results.
Mechanical Properties of Powder Injection Molded Ni-Based Superalloys
Authors: Gulsoy H. Ozkan , Ozbek Sunullah , Gunay Volkan , Baykara Tarik
Published: July 2011

This paper describes the microstructural and mechanical properties of powder injection moulded (PIM) Ni based superalloys. Ni-based superalloys were mixed with a polymeric binder (paraffin wax, carnauba wax, stearic acid and PP) and injection moulded as standard tensile bars. The critical powder loading for injection moulding were 62.5 vol. % for standard samples. Binder removal, debinding, was performed using a two-step solvent/thermal method. After debinding the samples were sintered at 1100°C and at 1285°C under high level vacuum. Metallographic studies were conducted to reveal the extent of densification and the corresponding microstructural changes. Ni 718, Ni 625 and Nimonic90 samples achieved high sintered densities via supersolidus liquid phase sintering. The mechanical properties of Ni 718, Ni 625 and Nimonic90 are determined and compared with the properties of previously reported studies on similar PIM materials.
Development and Application of Heat-Conductor Technique for Single Crystal Components of Superalloys
Authors: Ma De Xin , Zhou Bin , Bührig-Polaczek Andreas
Published: July 2011

During single crystal (SC) solidification in turbine blades of superalloys, grain defects often form in the platform region with abrupt variation in cross-section. In order to reduce grain defects induced by component geometries, a Heat Conductor (HC) technique was developed and applied to the production of SC turbine blades. The corresponding ceramic shell moulds were produced by a modified investment casting procedure. The heat conductors with excellent heat conductivity were inserted close to the inner corners of the platform, to effectively extract the local heat during directional solidification. Both computer simulation and temperature measurements have shown that this technique is able to produce a clear improvement of the thermal condition in the critical region of the components. The SC growth in the blade body can spread into the platform more quickly before the melt at the extremity becomes deeply undercooled. Microstructure investigations reveal a remarkable reduction in grain defect formation, providing confirmation of the effectiveness of the HC technique in improving the casting quality of SC components.
On Localized Deformation and Recrystallization as Damage Mechanisms during Thermomechanical Fatigue of Single Crystal Nickel-Based Superalloys
Authors: Moverare Johan J. , Sato Atsushi , Johansson Sten , Hasselqvist Magnus , Reed Roger C. , Kanesund Jan , Simonsson Kjell
Published: July 2011

Thermomechanical fatigue (TMF) in superalloys is growing in importance due to the introduction of advanced cooling systems but also due to the changes in demand and competition within the power generation market; this is requiring many power plants to operate under cyclic conditions. In this paper the TMF behaviour of three different single crystal nickel-based superalloys are compared. It is demonstrated that the deformation and damage mechanisms occurring during TMF are rather different from those traditionally reported for creep or isothermal fatigue. In all cases examined, the deformation is localized within a rather small number of deformation bands. While these bands were found to consist mainly of micro-twins in some alloys, in others they might be better described as slip or shear bands. Furthermore, in some circumstances these bands are prone to recrystallization. In CMSX-4, the intersection points of twins of different orientation act as initiation sites for this process. In the SCA425 alloy – of smaller gamma’ content, lower creep resistance and less great oxidation resistance – twinning is observed infrequently; however the deformation is still very localized and in the distorted gamma-gamma’ microstructure, along the shear bands, recrystallization is observed. Furthermore the recrystallization is enhanced by oxidation due to the development of a gamma’-depleted zone. In CMSX-4, TCP phases precipitated during long term ageing cause a more dispersed deformation behaviour which prevents recrystallization. Our findings confirm the importance of an inhomogeneous microstructure for good TMF resistance.
A Mathematical Framework for Cyclic Life Prediction of Directionally Solidified Nickel Superalloys
Authors: Mücke Roland
Published: July 2011

Modern gas turbines utilize single crystal (SX) and directionally solidified (DS) nickel superalloys which hold a higher cyclic life resistance and an improved creep rupture strength compared to their conventionally cast (CC) version. Both, SX and DS materials feature a significant direction dependence of material properties, which needs to be considered in the constitutive and lifing models. In this context, the paper presents a mathematical framework of cyclic life prediction. Although the method is developed for DS nickel alloys with transverse isotropic material behaviour, a generalisation to common orthotropic materials inclu¬ding SX is straightforward. The proposed procedure is validated by two examples. Moreover, an application to turbine components is shown.
Time and Temperature Dependent Cyclic Plasticity and Fatigue Crack Growth of the Nickel-Base Alloy617B – Experiments and Models
Authors: Maier Gerhard , Riedel Hermann , Seifert Thomas , Klöwer Jutta , Mohmann Ralf
Published: July 2011

Isothermal low cycle fatigue and thermomechanical fatigue tests are performed on Alloy617B in the solution-annealed and stabilized condition at temperatures between room temperature and 900 °C. In addition, the replica technique is applied to study the growth of microcracks. The Chaboche model is found to describe the cyclic viscoplastic behavior of both heats, except the pronounced cyclic hardening in the low-temperature branches of the TMF tests. A lifetime model based on the cyclic crack-tip opening displacement and the cyclic J integral is used to describe the measured lifetimes and crack growth rates. However, the description is not fully consistent, since the data for room temperature and for temperatures above 400 °C fall into two separate scatter bands.
Analysis of the Effective and Internal Cyclic Stress Components in the Inconel Superalloy Fatigued at Elevated Temperature
Authors: Šmíd Miroslav , Petrenec Martin , Polák Jaroslav , Obrtlík Karel , Chlupová Alice
Published: July 2011

Cyclic multiple step test in strain control have been performed on cylindrical specimens of cast polycrystalline Inconel 738LC and 792-5A superalloys at 800 °C in laboratory atmosphere. Hysteresis loops were analyzed according to the statistical theory of hysteresis loop. The effective and internal stress components were evaluated. The effective stress of γ´ precipitate has significant influence on the stress-strain response both materials. The stress amplitude in IN 792-5A is higher than in IN 738LC at approximately same total strain amplitude due to significantly higher effective stress of γ´ phase. Cyclic hardening/softening curves and cyclic stress-strain curves using short-cut procedure were obtained. Cyclic hardening/softening behavior depends both on temperature and strain amplitude. Low amplitude straining is characterized by the saturation of the stress amplitude. In high amplitude straining slight softening was found. The cyclic stress-strain curves for both materials can be fitted by power law. Cyclic stress-strain response in terms of internal and effective stress components is discussed in relation to microstructural parameters of the materials. The observation of surface relief revealed the presence of persistent slip markings.
Investigation of Freckle Formation under Various Solidification Conditions
Authors: Ma De Xin , Zhou Bin , Bührig-Polaczek Andreas
Published: July 2011

In the present work the influence of process parameters on freckle formation in superalloy CMSX-4 is demonstrated. A series of experiments were carried out using a laboratory furnace of Bridgman-type in which the temperature gradient G and solidification velocity V can be precisely controlled and individually varied over a wide range. On the etched surface and longitudinal sections of the quenched samples the formation and evolution of freckles were investigated. The initiation position of the freckles within the mushy zone was then determined. Based on the experimental observations a complete diagram was plotted to indicate the probability of freckle occurrence which is related to solidification parameters G and V. In this freckling map the freckle region is delimited by different criteria. Freckles arise only within a certain G/V-range for columnar dendrite growth; otherwise the solidification structure changes into cellular or equiaxed structure, depending on whether G/V-value increases or decreases. In comparison with the well-known freckling map of Copley et al., some new freckle-free regions are proposed. It is interesting to note that the freckle formation is also suppressed at very low cooling rates. In addition, the initiation position of the freckle formation in the mushy region was determined to be less than 2 mm below the dendrite tip of the solidification front.
Characterization of the Weld Line Zones of an Inertia Friction Welded Superalloy
Authors: Huang Z W , Li Hangyue , Baxter Gavin , Bray Simon , Bowen Paul
Published: July 2011

The Inertia Friction Welding (IFW) process is a high-temperature and high pressure process, with heavy plastic deformation, high power density, fast heating and fast cooling of the weld material. The microstructure produced in the weld line （WL）zones is therefore very different from parent material. A detailed microstructural investigation of the WL zones has been conducted using transmission electron microscopy and scanning electron microscopy. It has been shown that the morphology, energy status and microchemistry of grain boundaries in the WL zones are quite different from those in the parent material. It is also observed that, compared to a bi-modal distribution of intragranular ¢ particles in the parent material, a unimodal distribution of very fine spherical ¢ particles is produced in high density in the WL zones. This work provides a detailed understanding of the physical and chemical changes occurring across the weld line.
Formation of a Protective Alumina Scale on Ni-Base Superalloys by Using the Halogen Effect
Authors: Zschau Hans Eberhard , Renusch Daniel , Masset Patrick J. , Schütze Michael
Published: July 2011

A new method is proposed to achieve a dense protective alumina scale for Ni-base superalloys with an Al-content lower than 10 wt.% at temperatures above 1000°C. The method is based on the halogen effect. Thermodynamical calculations show the existence of a region for a positive fluorine effect at temperatures between 900-1200°C for the alloys IN738 and IN939. By using fluorine ion implantation in combination with Monte Carlo simulation of the fluorine profiles these results were transformed into a region of F-concentrations at the metal surface. A dense protective alumina scale was formed for IN738 after oxidation at 1050°C. Due to the very low Al-content no alumina scale was found for IN939.
Increased Wear and Oxidation Resistance of Titanium Aluminide Alloys by Laser Cladding
Authors: Ocylok Sörn , Weisheit Andreas , Kelbassa Ingomar
Published: July 2011

A process layout for laser cladding of layers on substrates of titanium aluminides using state-of-the-art and modified (additions of Si and TiB2) TiAl alloys is presented. The process involves a preheating of the samples to reduce thermal stresses and cladding in an inert gas atmosphere with an oxygen content lower than 30 ppm. These conditions lead to crack free layers and low surface oxidation. Microstructure and hardness of the layers are investigated. The abrasive wear resistance of the cladded layers in comparison to the base material is tested with promising results. Finally results of the oxidation behavior are shown and prove the increased performance of modified TiAl layers in comparison to the base material.
Microstructural Evolution of Mo-Si-B Ternary Alloys through Heat Treatment at 1800°C
Authors: Yoshimi Kyosuke , Ha Soeng Ho , Maruyama Kouichi , Tu Rong , Goto Takashi
Published: July 2011

First of all, the as-cast microstructures of Mo-rich Mo-Si-B ternary alloys were investigated around the triple junction point of the primary Mo solid solution, Mo5SiB2 and Mo2B in this work, based on the liquidus projections of the Mo-Si-B system which have been reported in earlier studies. Subsequently, their microstructural evolution through heat treatment was investigated. Since Mo2B crystallizes out during solidification into a primary or secondary phase even though the alloy composition lies in the triangle of Mo-Mo5SiB2-Mo3Si in the Mo-Si-B equilibrium phase diagram, the as-cast microstructures include the non-equilibrated Mo2B in wide compositional ranges. However, Mo2B was completely decomposed during heat treatment at 1800 °C for 24 h and this contributed to the development of homogeneous, fine microstructures. On the other hand, since Mo2B was not decomposed perfectly during 24 h of 1600 °C heat treatment, as-cast microstructures largely remained. Therefore, it is realized that the heat treatment at 1800 °C is necessary to obtain well-developed microstructures of Mo-Si-B alloys.
Microstructural Properties of Nb-Si Based Alloys Manufactured by Powder Metallurgy
Authors: Drawin Stefan , Monchoux J.P. , Raviart J.L. , Couret Alain
Published: July 2011

An NbTiHfCrAlSi niobium silicide based atomized powder has been compacted by a conventional technique (hot extrusion) and by spark plasma sintering to nearly fully dense alloys. Both materials exhibit a metastable fine micrometer-sized microstructure that has been coarsened by a subsequent heat treatment. The densification of the SPS sample takes place between ca. 800°C and 1300°C.
Design Considerations and Strengthening Mechanisms in Developing Co-Re-Based Alloys for Applications at + 100°C above Ni-Superalloys
Authors: Mukherji Debashis , Rösler Joachim
Published: July 2011

Although Ni-base superalloys meet the gas turbine needs of today, they are used very close to their melting range. Demands for applications at higher temperatures are presently met partly through component cooling and application of thermal barrier coatings. However, this approach can not be sustained indefinitely unless the base metal melting temperature is also significantly increased. Rhenium addition can substantially increase the melting point in Co-base alloys and thereby provide a unique opportunity in the development of new alloys for very high temperatures – e.g. for applications at +100°C metal temperature above present day single crystal Ni-base superalloys. The design considerations behind the Co-Re alloy development are presented in this paper. Selected results from the alloy development studies are also presented.
High-Temperature Oxidation Behaviour of Co-Re-Cr-Based Alloys: Limitations and Ways to Improve
Authors: Gorr Bronislava , Christ Hans-Jürgen
Published: July 2011

Ni-based alloys are the most widely used alloy system in high-temperature applications. However, the use of Ni-based alloys is limited to temperatures below 1100°C. The experimental Co-Re-Cr-based alloys are promising for high-temperature applications for service temperatures beyond 1200°C. A complete miscibility in the Co-Re system allows to steadily elevate the melting point of the system with the rhenium content. In addition, rhenium takes the role as solid solution strengthening element. In the case of Co-based alloys, the oxidation resistance at high temperature is mainly based on the formation of a protective Cr2O3 scale. The purpose of the present investigations is to gain an insight into the oxidation mechanisms of the model Co-Re-Cr alloys and to find ways to improve oxidation resistance of this class of materials. Earlier investigations of the authors showed a rather poor oxidation resistance during exposure to laboratory air. Oxidation at 1000°C in air yielded an oxide scale that consists of a Co-oxide outer layer on a thick and porous Co-Cr oxide and a semicontinuous and therefore non-protective Cr-oxide film on the base metal substrate. As a consequence of the lacking protectiveness of the oxide layer the vaporization of rhenium oxide takes place and hence leads to a rapid loss of Re. The aim of recent investigations is to study the effect of Si on the high-temperature oxidation behaviour of Co-Re-Cr alloys by means of kinetic and microstructural examinations. It was found that Si stabilizes the Cr2O3 scale, enhancing the oxidation resistance significantly. Hence, the synergetic effect of chromium with silicon could be considered as an encouraging perspective to improve the oxidation resistance of Co-Re-Cr alloys. Apart from that, other concepts to enhance the oxidation resistance of this class of materials are discussed, such as the formation of a borosilicate layer or protective Al2O3 scale on the substrate surface.
Use of Alloy 59 for the Transport of Highly Corrosive Dangerous Goods
Authors: Weltschev Margit , Baessler Ralph
Published: July 2011

Alloy 59 (NiCr23Mo16Al) with a lot of chromium, molybdenum and nickel possesses excellent resistance not only to reducing but also oxidizing chemicals. Both the Nickel alloy 59 and the superaustenitic steel alloy 31 have already been used as shell materials for tank vehicles or tank containers. Use of these alloys allows the transport of a signifi-cantly more wider variety of chemicals and, especially, waste mixtures than the use of common aus-tenitic steels. Another advantage is the extension of test intervals of for transport tanks. In Germany the “BAM-List – Requirements for Tanks for the Transport of Dangerous Goods” is the basis for substance-related prototype approvals for tank containers designed for the car¬ri¬age of dangerous goods issued by the Federal Institute for Materials Re¬search and Testing (BAM). Com-patibility evaluations of selected metallic material groups as well as polymeric gasket and lining materials under the influence of approximately 7000 dangerous goods and water-polluting sub-stances are published in the BAM-List. Alloy 59 belongs to the group of metallic materials in the BAM-List. Due to the large number of dangerous goods in the BAM-List BAM, IKS Dresden and ThyssenKrupp VDM performed a comprehensive corrosion test programme with welded specimens of the nickel alloy 59 and the superaustenitic steels alloy 926 and alloy 31 in the period 2002 - 2010. Especially In particular alloy 59 and alloy 31 were exposed to a large number of corrosive sub-stances such as various mixtures of both nitric acid/sulphuric acid and nitric acid/phosphoric acid at 55 °C. Other corrosive test substances were different organic and inorganic halogenides, peroxyace-tic acid and molten substances. In the case of molten chemicals such as monochloroacetic acid the test temperature was increased to more than 100 °C. The test results presented in this paper are al-ready included in the 10th edition of the BAM-List and, therefore, available to the customer.
Characterization of Single-Crystal Dendrite Structure and Porosity in Nickel-Based Superalloys Using X-Ray Micro-Computed Tomography
Authors: Jaroszewicz Jakub , Matysiak Hubert , Michalski Jakub , Matuszewski Kamil , Kubiak Krzysztof , Kurzydlowski Krzysztof Jan
Published: July 2011

X-ray micro-computed tomography system has been used for visualization in two- (2-D) and three dimensions (3-D) of the dendrite structure and pores in single-crystals fabricated by Bridgman investment casting technique. The system described in the paper reconstructs 3-D geometry from a set of 2-D images obtained by multiple slicing of an X-ray radiography image. The results obtained in this study demonstrate the effect of withdrawal rate on the primary dendrite arm spacing and porosity in single-crystal made of CMSX-4 alloy.
Effect of HIP Parameters on the Micro-Structural Evolution of a Single Crystal Ni-Based Superalloy
Authors: Lopez-Galilea Inmaculada , Huth Stephan , Bartsch Marion , Theisen Werner
Published: July 2011

For reducing the porosity of single crystal (SX) nickel-based superalloys, Hot Isostatic Pressing (HIP) is used. High pressures of about 100-170 MPa lead to local deformation, which close the pores. However, since HIP also requires high temperatures (1000-1200°C) it has a pronounced effect on the microstructure and the local distribution of elements. This contribution analyses the effect of different HIP treatments on both the microstructure and the segregation of the SX superalloy LEK94 in the as-precipitation-hardened state. In addition, the effects of rapid or slow cooling are analyzed. To distinguish the effect of pressure from those of temperature, the HIPed samples are compared with specimens annealed at atmospheric pressure.
A Review of the Measurement of Single Crystal Orientation Parameters of Nickel Castings
Authors: Clay K. , Quested P.N. , Morrell Roger , Mingard Ken P.
Published: July 2011

Control of single crystal orientation in modern gas turbine components is a critical quality control issue for optimum reliable behaviour, and an increasingly important aspect of trade. This paper reviews industrial practice for the determination of primary crystal orientation and for the determination of 'disorientation' (R-value) between sub-grains. Different techniques and measurement conventions are compared, and the errors of measurement have been assessed through a European round-robin. Causes of poor reproducibility in 'disorientation' measurement have been identified by EBSD investigations. Recommendations for unified practice have been made in a Good Practice Guide as a precursor to a new industry-wide standard.
Chemical Composition and Structure of the Boride Inclusions in Synthetic Diamonds Grown under HPHT
Authors: Gong Jian Hong , Lin Shu Xia , Gao Jun
Published: July 2011

Boride inclusions in the synthetic diamond single crystals grown from Fe-Ni-C-B system under high temperature and high pressure were studied in the present paper. Both chemical composition and structure of the inclusions incorporated into the diamond during the process of diamond growth were successfully determined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the inclusions related to boron trapped in the diamond consisted of f.c.c. (FeNi)23(CB)6, (FeNi)3(CB), Fe2B, FeB, hexagonal Ni3B, and B4C.
A New Hole Filling Algorithm in Space for Triangular Model
Authors: Chen Jie , Gao Cheng Hui , He Bing Wei
Published: July 2011

Aiming at filling the holes which were generated from uncompleted point cloud data in reverse engineering, a new hole filling algorithm in space is presented. Firstly, the holes boundary was identified and pretreated, and the hole boundary feature datum was established and the boundary was projected on it to form a projection polygon. Secondly, the smallest angle of the projection polygon was found out to determine the corresponding boundary point as the mesh growing point. The original hole was covered by the new meshes covering and then filling algorithm was completed. Finally, the neighborhood points of hole boundary vertex were selected as the sampling points for the least squares fitting adjustment of new filled vertices position, which aims at the preparation hole filled result. Examples are given to prove that the method has good accuracy and stability of the hole filling.
Numerical Analysis of Co-Cured Composite Single Lap Joint with Spew Fillets
Authors: Zhao Guo Hua , Shu Qing Lian , Huang Bo Sheng
Published: July 2011

Spew fillet is common in co-cured composite single lap joint. It plays an important role in the safety of the joint. But few attentions were paid to the subject in former investigations. In this paper, co-cured composite single lap joints with spew fillets under static tensile load were investigated numerically using the commercial finite element code ANSYS. The submodeling technique was employed to overcome the problem caused by extra aspect ratio of elements. The computation results indicated that the existence of spew fillets will not change the possible failure location, but will improve the anti-failure performance of single lap joint.
An Alkaline SiO2 Slurry for Fine Atomizing CMP
Authors: Zhai Jing , Ni Zi Feng , Li Qing Zhong
Published: July 2011

A kind of slurry which is applicable for fine atomizing CMP was made and the optimal results were obtained through orthogonal experiments by comparing fine atomizing CMP and traditional CMP. The research results show that the material removal rate of fine atomizing CMP is 52.23% of traditional CMP, and the dosage of the slurry used in fine atomizing CMP only accounts for 10 vol% compared to traditional CMP. The surface roughness after the fine atomizing CMP is 2.5nm which is better than that of the traditional CMP (3.0nm).
Synthesis and Simplification of Fractal Profile
Authors: Zhou Chao , Gao Cheng Hui , Chen Jie , Lai Lian Feng
Published: July 2011

In order to import a synthesized fractal profile into finite element software, the profile synthesized by discrete Fourier transform was studied. The synthesized profile was filtered in frequency domain in order to filter its high frequency components and to make it smooth, and then the chord deviation algorithm was used to reduce its redundant data in space domain. It was found that: after filtering, the profile is smooth but with lots of redundant data; the chord deviation algorithm can simplify the profile which is redundant in space domain; the time needed in the process of importing a profile into finite element software can be reduced greatly after profile simplification.
The Investigation of Creep Behavior for NiAl-28Cr-5.5Mo-0.5Hf-0.02wt.%P Alloy at High Temperature
Authors: Zhang Guang Ye , Ye Dong Wen , Wang Jin Lin , Chen You Ming , Liu Long Fei , Guo Yuan Jun
Published: July 2011

The Microstructure and creep behavior for NiAl-28Cr-5.5Mo-0.5Hf-0.02wt.%P alloy at high temperature have been investigated in this paper. The results reveal that the high temperature creep behavior of the NiAl-28Cr-5.5Mo-0.5Hf-0.02wt.%P alloy is characterized by transient primary creep and dominant steady-state creep as well as ternary creep behavior. The primary creep can be described by Garofalo equation and the steady-state creep can be depicted by Dorn equation. The creep mechanisms are viscous glide of dislocations at lower and middle testing temperatures and dislocation climb at higher temperature. No change of the microstructure for the testing alloy indicates that the creep fracture is controlled by the formation and propagation of cavities and cracks, and the creep fracture behavior obeys Monk man-Grant relationship.
Development for the Comprehensive Optimization Technology of Process Lubrication Regime in Double Cold Reduction
Authors: Bai Zhen Hua , Si Hong Xin , Zhou Qing Tian , Li Xiu Jun , Wu Shou Min , Shi Xiao Dong
Published: July 2011

The setting goals of process lubrication were not all-inclusive in the previous manufacturer of double cold reduction. Strip shape, surface quality, the fuel consumption of unit and rolling stability could not be considered comprehensively. Aimed at the equipment and production craft characters of double cold reduction unit, at the basis of putting forward the comprehensive control index of a strip-shaped fuel consumption cleanliness for the first time, ensuring the shape quality of strip, lowering the oil residue on strip surface, improving the cleanliness of strip surface and reducing fuel consumption were defined as control targets; besides, the control of slip and heat-scratches were defined as constraints. A complete comprehensive optimization technology of process lubrication regime was established and has been applied to a 1220 double cold reduction unit belonging to Baosteel in China. Rolling speed, surface quality and strip shape quality are improved effectively, and oil consumption is reduced, meanwhile, the productivity and rolling yield of unit are ensured. This technology has created economic benefits for domestic steel makers and has further extended application value.
Virtual Instrument for Weak Signal Detecting on Monostable Stochastic Resonance
Authors: Yuan Quan , Shen Yan , Chen Liang
Published: July 2011

Stochastic resonance (SR) is a nonlinear phenomenon which can be used to detect weak signal. The theory of SR in a biased mono-stable system driven by multiplicative and additive white noise as well as a weak periodic signal is investigated. The virtual instrument (VI) for weak signal detecting based on this theory is designed with LabVIEW. This instrument can be used to detect weak periodic signals which meets the conditions given and can greatly improved the power spectrum of the weak signal. The results that related to different sets of parameters are given and the features of these results are in accordance with the theory of mono-stable SR. Thus, the application of this theory in the detecting of weak signal is proven to be valid.
Period-Varying Sampling Scheme for Networked Control Systems
Authors: Shen Yan , Guo Bing
Published: July 2011

In the networked control systems, control performance and network performance are closely related to the sampling period influenced by the network-induced delay. So in order to improve the network performance by adjusting the current sampling period, a period-vary sampling scheme is proposed based on an adjuster for the sampling period designed. In this scheme, the adjuster consists of a monitor, which acquires network resources utilization and the executive time of data packet, and a predictor, which uses BP neural network to predict the next sampling period by utilizing network resources utilization and data packet executive time. The simulation results show that the proposed scheme can alleviate the influence of time delay and improve the performance of the networked control systems.
An Image Encryption Method Based on Tent Chaotic Map in DCT Domain
Authors: Song Jian Hua , Ding Qun
Published: July 2011

In recent years, the chaos based cryptographic algorithms have suggested some new and efficient ways to develop secure image encryption techniques. In this paper, the sequence was generated using chaotic system, combined with high efficiency and better security in transform domain. An image encryption method based on Tent chaotic map in DCT domain was proposed. The simulation results show that this method has characteristics such as high efficiency and good safety, and has a certain practicality and objectivity.
A Study on the Phase Transformation Behavior and Characteristics of BaTi1-X(Li2/3 Nb2/3 )XO3 Solid Solution
Authors: Wu Peng , Zhang Jing Ji , Sun Li Na , Liu Jing Tao , Zhou Huang , Jin Sheng Yong , Wang Jiang Ying
Published: July 2011

Microstructure, phase transformation behavior and electrical properties of BaTi1-x(Li2/3Nb2/3)xO3 with x=0.01-0.40 ceramics have been investigated. Only perovskite phase is detected for all the compositions. The room temperature state of BaTi1-x(Li2/3Nb2/3)xO3 ceramics experiences a transformation from a ferroelectric phase to a paraelectric phase with increasing x. Meanwhile, the permittivity of BaTi1-x(Li2/3Nb2/3)xO3 ceramics reduces, while the Q×f value increases. A degree of frequency dispersion of dielectric peak is obviously increased as x increases from 0.01 to 0.10. It is of great interest that a dielectric abnormity represented by a broad dielectric peak at 200-400K is observed for the composition with x=0.40.
Experimental Research of Testing Methods for Vibration Characteristics
Authors: Bu Na Rui , Zhang Shi Lian , Cui Wei Long
Published: July 2011

The vibration characteristics of the structure are important parameters of structural design if want to accurately grasp the vibration characteristics of the structure, the testing methods must be proper. At the present time, pulsation, free vibration, vibrating load are the common methods, This article adopts pulsation, knocking, initial displacement, white noise sweeping, and simple harmonic waves knocking to test the vibration characteristics of the structure and studies the characteristics of those testing methods.