bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the Strength and Ductility of Magnesium Alloys by Grain Refinement and Texture Modification
Authors: Liu T. , Wang Yan Dong , Wu Shi Ding , Li Shou Xin , Peng Ru Lin , Xu Yong Bo
Published: March 2009

The room temperature tensile strength and ductility of Mg-3.3%Li alloy were
improved simultaneously by two kinds of different equal channel angular pressing (ECAP) treatments. Microstructural analyses showed that grain refinement and texture modification are the principal reasons for the improvement of mechanical properties.
Dynamic Recrystallization and Microstructure Evolution in AZ31 Magnesium Alloy during Thermomechanical Processing
Authors: Huang Guang Jie , Wang Ling Yun , Huang Guang Sheng , Pan Fu Sheng
Published: March 2009

The deformation behavior of AZ31 magnesium alloy has been investigated by isothermal compression at temperatures between 573-723K and at constant strain rates ranging from 10-3 -1s-1. It is shown that the form of flow stress curves is very sensitive to temperature and strain rate. In the experimental domain studied, the flow stresses are modeled using a power law with an average activation energy of 145.16 kJ/mol, and dynamic recrystallization (DRX) occurs. The critical strain
for DRX is determined by analysis of flow stress curves. The ratio of the critical strain to the peak strain falls in the range of 0.4-0.5. At low temperatures and high strai rates, the deformation become macroscopically inhomogeneous, and the fracture of the specimens is accompanied by shear banding. Grain refinement resulting from DRX is less effective at high temperatures due to rapid grain growth. It is also shown that there is no difference between peak stress and stable state stress at high temperatures and lower strain rates, presenting the feature of continuous dynamic recrystallization (CDRX).
Effects of Variable La/Ce Ratio on Microstructure and Mechanical Properties of Mg-5Al-0.3Mn-1RE Alloys
Authors: He Shang Ming , Peng Li Ming , Zeng Xiao Qin , Liu Li Peng , Wang Qu Dong , Ding Wen Jiang , Zhu Yan Ping
Published: March 2009

Effects of variable La/Ce ratio on microstructure and mechanical properties of
Mg-5Al-0.3Mn-1RE alloys were investigated. The results indicated that pure La or pure Ce can improve ultimate strength and yield strength of AM50 effectively without obvious decrease of elongation, and the effect of La is better than that of Ce. However, addition of La and Ce together deteriorates the mechanical properties of AM50, and the valley of mechanical properties mostly appears on La:Ce= 1:1. The existence of coarse skeleton-like phase and less amount of Mg17Al12 phase is responsible for this.
General Situation of the Series Recovery Equipments for the Scraps of Magnesium Alloy in China
Authors: Tian Xin Li , Luo Qin , Dong Qing
Published: March 2009

The technology of the domestic-manufacture of the whole-set recovery equipment for the scraps of magnesium alloy has almost finished in China. According to the request of the process of the recycle of the scraps of magnesium alloy and the key technology, the general situation of the whole-setting of related domestic-manufactured equipments, the technology parameters of the main technological equipments and the plan for the development in the future described. The key
technological indexes of domestic-manufactured equipments for quantitative outputting the melted magnesium alloy and domestic-manufactured multiple-protecting-gas commingling equipments keeps are as advanced or better than the overseas technologies of the similar equipments.
Development of the Rheo-Diecasting Process for Mg-Alloys
Authors: Fan Z. , Ji Shouxun , Liu Guo Jun
Published: March 2009

Research on rheology of semisolid slurries suggests that an ideal semisolid slurry for
semisolid metal (SSM) processing is one in which a suitable volume fraction of fine and spherical particles dispersed uniformly in a liquid matrix. Such ideal semisolid slurry can be obtained by enhancing the effective nucleation and promoting spherical growth during solidification. Experimental investigation and theoretical analysis of solidification under forced convection allowed us to identify the conditions for achieving enhanced effective nucleation and promotion of spherical growth. Such conditions can be summarised as uniform temperature and chemistry throughout the whole volume of liquid alloy, high shear rate and high intensity of turbulence during the solidification process. Based on such understandings, a new SSM processing technology, rheodiecasting (RDC), has been developed for the production of components with high integrity. AZ91D Mg-alloy was used to optimise the rheo-diecasting process and component production
trials. The experimental results indicate that the rheo-diecast samples have close-to-zero porosity, fine and uniform microstructure and much improved strength and ductility. Rheo-diecasting process is particularly suitable for production of high-safety, airtight and highly stressed components in the automotive industry.
Warm Lateral Extrusion of Magnesium Wrought Alloy by Using Multi-Axes Material Testing Machine
Authors: Hatsukano Kanichi , Matsuzaki Kunio , Shimizu Toru , Shinozaki Kichitaro
Published: March 2009

The Formability of magnesium wrought alloys, AZ61 and AZ31 were investigated . First, the cylinder compression tests were carried out at room temperature and elevated temperatures. Then, the possibility of applying the warm lateral extrusion of the AZ61 and AZ31 alloys were examined under several conditions by using the multi-axes material testing machine. A cylindrical billet coated with molybdenum disulfide lubricant was set in the horizontal die cavity and the billet was heated up
to the extrusion temperature, and then extruded laterally under the two horizontally advancing punches. Furthermore, lateral extrusion with counteracting pressure on the end of branches by using two punches methods was tried to reduce the extrusion temperature and sound products was obtained around 190°C.
Effects of Manganese Contents on Extruded Magnesium Alloys
Authors: Murai Tsutomu , Oguri Hajime , Matsuoka Shin-ichi
Published: March 2009

Effects of manganese contents in AZ31 and AZ10 on billets microstructure, extrusion
loads, occurring of surface cracks and mechanical properties were investigated. In the range 0 to 0.8% manganese content, there exist an adequate manganese content for avoiding surface cracks and obtaining the highest tensile strength.
Safety Design of a Horizontal Semi-Continuous Caster for Magnesium Alloy
Authors: Luo Qin , Dong Qing , Yang Zuyuan
Published: March 2009

The process of the safety design process, the structure principle and the key technology are described. The technology of dual molder, gas-water combined condensation, online fire fighting and infrared thermo-induction automatic disconnecting relief valve is used in this machine, which , compared to the current domestic “erect-pit output” technology, enjoys higher security & reliability during the production, higher effiiciency and better stability of the products. It perfectly meets the demand of the “horizontal output” process.
An Investigation of Low Temperature Superplasticity of ZK40 Magnesium Alloy Subjected to Equal Channel Angular Pressing
Authors: Lin Li , Chen Li Jia , Liu Zhen
Published: March 2009

Microstructure evolution and superplastic behaviors of ZK40 magnesium alloy were
investigated in the temperature range of 473 ~ 623 K. Twinning occurred significantly after being processed by equal channel angular pressing (ECAP) for one pass through the die, the mean grain size was 5.6 µm. Finer grains can be obtained after further processing through ECAP, the average grain size of the alloy processed by ECAP for three passes was as low as 0.8 µm; this alloy exhibited low temperature superplasticity at 473 ~ 523 K, elongations at an initial strain rate of 1×10-3 s-1 were 260 % at 473 K and 612 % at 523 K, respectively. The incompatibility between fine
and coarse grains was thought to be unfavorable to the improvement of superplasticity. Low temperature superplasticity of the as-ECAP ZK40 alloy can be attributed to the relatively finer grain size and the homogeneity of microstructure.
Microstructure Evolution and Mechanical Properties of AZ 31 Mg Alloy Processed by Equal Channel Angular Extrusion
Authors: Jin Li , Lin Dong Liang , Mao Da Li , Zeng Xiao Qin , Ding Wen Jiang
Published: March 2009

Microstructure evolution and mechanical properties of AZ31 Mg alloy during equal
channel angular extrusion (ECAE) at the temperature range of 453-498K was investigated. The processing temperature is an important factor to affect the microstructure and mechanical properties of the Mg alloy during ECAE. ECAE processing can be practiced at 498k or upon the temperature for as-received AZ31 alloy. A new two-step ECAEed processing was successfully used with lowing
the processing temperature to 453k. The ductility increased but yield stress decreased though the grain refinement after ECAE at 498k because the recrystallization took place and large angle grain boundary formed. However both the ductility and yield stress were increased after two-step ECAE, which was ascribed to grain refinement as well as incomplete dynamic recovery and recrystallization during the processing.
A New Low GWP Protective Atmosphere Containing HFC-152a for Molten Magnesium against Ignition
Authors: Zeng Yi-wen , Peng Li Ming , Mao Xie Min , Zeng Xiao Qin , Ding Wen Jiang
Published: March 2009

Sulphur hexafluoride (SF6) is widely used by the magnesium industry as a protective atmosphere. It has been demonstrated that SF6 prevents molten magnesium from further oxidation by reacting with magnesium to make the surface film on the magnesium melt denser. However, due to its high greenhouse effect (GWP=23900), the alternatives of SF6 must be sought. In this paper, 1,1-difluoroethane (commercially named HFC-152a), whose GWP value is only 140 and far lower than that of SF6, was tested to check its capacity of ignition-proof and further-oxidation-proof. Similar to SF6, the melt’s surface film formed in the protective atmosphere containing HFC-152a has a shiny metallic appearance. The surface film’s microstructure has been characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD’s results showed that the film contains only MgO and MgF2 phases while SEM showed their morphologies are uniform.
Microstructures and Creep of AM50-Sb-Gd Alloys
Authors: Tian Su Gui , Sohn Keun Yong , Cho Hyun Gap , Kim Kyung Hyun
Published: March 2009

Creep behavior of AM50-0.4% Sb-0.9%Gd alloy has been studied at temperatures
ranging from 150 to 200°C and at stresses ranging from 40 to 90 MPa. Results show that the creep rate of AM50-0.4%Sb-0.9%Gd alloy was mainly controlled by dislocation climb at low stresses under 50 MPa. The activation energy for the creep was 131.2 ± 10 kJ/mol and the stress exponent was in the range from 4 to 9 depending on the applied stress. More than one deformation-mechanism were involved during the creep of this alloy. Microstructures of the alloy consist of a–Mg matrix and fine particles, distinguished as Mg17Al12, Sb2Mg3, and Mg2Gd or Al7GdMn5 that were homogeneously distributed in the matrix of the alloy, which effectively reduced the movement of dislocations, enhancing the creep resistance. Many dislocations were identified to be present on non-basal planes after creep deformation.
Flow Stress and Microstructural Evolution of AM50 Alloy during Upsetting Forging Tests at High Temperature
Authors: Yan Yun Qi , Zhou Lian , Chen Chang Qi
Published: March 2009

Flow stress and microstructures evolution of AM50 alloy during upsetting forging tests were investigated in this paper. In upsetting forging deformation, cylindrical billets of AM50 alloy as-cast were compressed in the temperature range of 250°C to 350°C and strain rate range of 1.1×10-3s-1 to 2.8×10-2s-1. Under the deformed conditions, the true stress-true strain curves indicated that the true stress increased quickly at the initial time, then stayed at certain value for a short duration and increased continuously at lower temperature and high strain rate. It should be noted that the true stress kept the dynamic balance with the true strain at higher temperature and lower strain rate that the true stress obeyed the regulation as the same as the ordinary materials. The peak stress at all conditions increased with the strain rate increasing and the forging temperature decreasing. A great many recrystallized grains and dislocations were observed in the deformed specimens of AM50 alloy. The grain size of the deformed specimens decreased with decreasing
forging temperature and increasing the deformation.
Materials Substitution for Scientific Use of Mg Castings on Motorbikes
Authors: Xu Shao Yong , Cao Han Xue , Long Si Yuan , Chen Xiaoan , Liu Zhen , Zhang Zhong He
Published: March 2009

To promote a technological use of Mg alloy castings on motorbike, a technical routine for material substitution was demonstratively presented with engine crankshaft case and motorbike wheels. It was shown that, subjected to failure analysis, comparative FEM analyses, structural redesign, numerical optimization of casting process and strict tests of prototypes, the service performance of the Mg castings can be ensured, in addition to the performance improvement stemming from the advantageous properties of Mg alloys.
Magnesium Advances and Applications in North America Automotive Industry
Authors: Li Nai Yi
Published: March 2009

Magnesium is increasingly becoming an attractive alternative to steel, aluminum, and
polymer composites for vehicle weight reduction due to its ability to meet vehicle performance requirements. To meet the Corporate Average Fuel Economy (CAFÉ) standard and to maximize the weight reduction of vehicles in the coming years, the magnesium applications are expected to increase significantly in both structural and powertrain components where material creep resistance is required. This first half of the paper will give an overview of recent automotive magnesium R&D programs including Light Metal Cast, Magnesium Powertrain Cast Components, and Structural Cast Magnesium Development supported by the United States Council for Automotive Research (USCAR) and the US Department of Energy. The USCAR is the umbrella organization of DaimlerChrysler Corporation, Ford Motor Company and General Motors, which was formed in 1992 to further strengthen the technology base of the US automotive industry through cooperative, pre-competitive research. During the last decade, the magnesium foundry industry has grown, yet
the material and manufacturing process costs of magnesium die-casting has impeded large-scale implementation into the automotive industry. As a result, Ford Motor Company initiated a Cost Reduced Magnesium Die Castings Using Heated Runners (CORMAG) program in partnership of the Advanced Technology Program of the US National Institute of Standards and Technology. The second half of this paper will briefly present the program goal, progress and its impact. In addition, this paper will present some magnesium applications, including a 2004 Ford F-150 light truck Front End Support Assembly and a 2005 Ford GT instrument panel structure.
Effect of Stress Wave in the Course of Metal Machining
Authors: Wang Li Tao , Wang Q.C.
Published: March 2009

It’s a key problem in the mechanical field that the machining stress and original stress redistribute in the workpiece when cutting. In the study of this problem, we found a phenomenon of stress wave in the cutting, as in dynamics; Because of the effect of stress wave, the machined workpieces with complicated structure may have more stress focuses, particularly, the aeronautic and astronautic products have many frame structures, the dynamic stress in the machining can undergo many changes because of the structure’s restrain, and leads to the stress focus in the corner of frame. This is the main factor to cause the workpiece distortion. So, the study of this paper is of great value to explain the law of pockety stress in the machined workpiece, and can help to determine reasonable technique to control and adjust the workpiece’s stress, and finally improve the quality of workpieces.
Simulation of the Residual Stress of Cold-Formed Thin-Wall Steel Members and Calculation of Load under Its Influence
Authors: Zhao Feng , Liu Hua Chen
Published: March 2009

Because of the particularity of distribution of the residual stress of cold-formed thin-wall steel members, now there has not yet been a proper method for directly considering the influence of the residual stress in calculating the reliable capacity of carrying load of cold-formed thin-wall steel members, and such is the typical case in China’s National Technical Specification of Cold-formed Thin-wall Steel Structures GB50018-2002. With the cold-formed thin-wall channel steel taken as specific object in this study as well as assumed to be ideal elastic-plastic body, their finite modular models are set up in ANSYS. According to the tested results and the distributing rules of residual stress, the models of the residual stress of cold-formed thin-wall channel steel are established close to the factual data, and also the initial stress file is set up that can describe the magnitude and distribution of the residual stress. The file has two features: first, it is likely to find out about the rules of the cold-steel residual stress varying in the direction of thickness by using the values of residual stress at some integral points in thickness direction of a specified module , and second, it is applicabled to simulate various distributions of residual stress. So the
ultimate load of the member can be worked out and elastic-plastic calculating problem
of cold-formed thin-walled steel sections can be easily solved by introducing the
initial stress file into the stability analysis of ANSYS.
The Sensitivity of Focusing, Parallel Beam and Mixed Optics to Alignment Errors in XRD Residual Stress Measurements
Authors: Vermeulen Arnold C.
Published: March 2009

The sensitivity of various combinations of optics to alignment errors is investigated. A
large number of tests with varying specimen displacements and incident beam misalignments are performed for both line and point focus residual stress optics combinations. This investigation includes experiments with mixed combinations of typical “focusing beam optics” and “parallel beam optics”. It is verified if the peak positions are either sensitive to height errors like for the focusing beam geometry or insensitive like for the parallel beam geometry. The peak position
sensitivity is classified for all combinations of incident beam and diffracted beam optics modules.
Surface Roughness Effect on Pseudo-GIXRD Stress Analysis
Authors: Peng Jun , Ji Vincent , Seiler Wilfrid
Published: March 2009

Residual stresses levels and their distributions in thin films have an important effect on their mechanical properties. The non-destructive analysis by pseudo-grazing incidence X-ray diffraction (GIXRD) allows us to define residual stresses gradients as a function of thin film depth. In case of pseudo-GXRD, we must take into account the effects due to surface roughness on residual stress analysis. We
have investigated firstly a set of carbon steel specimens with different surface
roughness (RZ varies from 4.2µm to 9.5µm) obtained by grinding. All specimens were tempered to eliminate the residual stresses due to machining. With K radiation of Chromium, Bragg peak positions were determined with various incidence angles  (varies from 1° to 78°) for each specimen. Secondly, a carbon steel specimen containing 4 zones with different surface roughness was loaded elastically in tension, pseudo-GIXRD has used for stress analysis on the loaded specimen with various incidence angles. The peak shifts due to the surface roughness were studied as function of different roughness and different incidence angles. The stress relaxation due to surface roughness was then studied.
Application of X-Ray and Neutron Diffraction Methods to Reliability Evaluation of Structural Components and Electronic Device
Authors: Hayashi Makoto , Okido Shinobu
Published: March 2009

In the X-ray diffraction method, the diffraction intensity, the half-value width, the residual stress and the amount of residual austenitic phase can be measured. By using these parameters, the quality, the mechanical properties and the fatigue strength of materials, the remaining life of fatigue and creep can be evaluated. While the X-ray study has been widely performed for the various kinds of industrial fields in the laboratory, the applications to the actual structure and components have not so many. However, the small size X-ray residual stress analyzer, the position sensitive detector and the micro area diffraction apparatus have been developed for these twenty years. Thus the X-ray diffraction methods have been variously applied to the
industrial fields. The X-ray diffraction methods were used to be applied for the large scale structures and machine parts, but recently applied to the semi-conductor fields. On the other hand, the neutron diffraction method has been introduced to measure the residual stresses in the internals of components because of its deep
penetration depth. Based on the experiences of X-ray diffraction method, the various kinds of techniques have been proposed. In this paper, the applications of X-ray and neutron diffraction method to the reliability evaluations of structural components and the electronic devices are described.
In Situ Neutron Diffraction Studies of Phase Transformations in Si - Mn TRIP Steel
Authors: Muránsky O. , Lukáš Petr , Sittner Petr , Zrník Jozef , Jenčuš P. , Nový Z.
Published: March 2009

High strength and ductility of the TRIP steels is often attributed to the transformation induced plasticity effect resulting from the strain induced martensitic transformation of the retained austenite in the bainite microstructure. The present work reports results of in-situ neutron diffraction experiments focused on monitoring the phase evolution in two TRIP steel samples (two different thermomechanical treatments) subjected to tensile loading at room temperature. Comparison of the single lineprofile analysis of reactor data (TKSN-400 at NPI Rez) and multi lineprofile analysis of
data obtained at spallation neutron source (diffractometer ENGIN-X at ISIS RAL Chilton) suggests that the former can be used in the first approximation for in-situ monitoring of the phase evolution in TRIP steels subjected to mechanical loads.
In Situ Synchrotron Measurements of Oxide Growth Strains
Authors: Almer Jonathan , Swift Geoffrey A. , Nychka John A. , Üstündag Ersan , Clarke David R.
Published: March 2009

Synchrotron x-rays are used for in situ determination of oxide strain, during oxide
formation on a Kanthal A1 FeCrAlZr substrate at 1160°C. The measurements rely on use of high-energy (~80keV) x-rays and transmission geometry, and the methodology of the strain measurements is presented. Oxide growth strains at
elevated temperature, relative to pure alumina, were seen to be small, while temperature excursions induced significant strains. Furthermore, significant strain
relaxation was observed during isothermal holds, suggesting oxide creep as a major
relaxation mechanism. Upon cooling to room temperature, significant residual strains
developed, with a corresponding in-plane residual stress of -3.7 GPa.
Effects of Stress Cycles on Surface Magnetic Field
Authors: Chen Xing , Li Lu Ming , Yang E. , Huang X.F.
Published: March 2009

The change of magnetic flux as a function of applied tensive stress has been investigated under geomagnetic field for a cuboid specimen of 0.45% wt C steel. A hole was drilled in the center of the specimen to generate stress concentration and the stress concentration of the specimen was theoretic calculated. The magnetic flux near the surface was measured using a reluctance effect sensor with sensitivity of 5 2 10 Gs − × in directions parallel and perpendicular to tensile direction. To
each specimen magnetic field distributions of 9 stress cycles, amplitude form 0kN to 120kN, were measured. The results showed a reversible dependence of this field on tensile after the first few stress cycles. Correlation coefficients of these data also show this trend. During the cycles, domain motion and rotation occurred in response to tensile stress. This change included reversible and irreversible process. After several tensile cycles at same stress amplitude, all irreversible components were overcome and the change of magnetic field became mostly reversible. Comparing
with the previous work, the reversible magnetic field versus tensile stress shows clearer and more valuable relationship between stress and field.
Depth Resolved Investigation of Friction Stir Welds Made from AA2024 / AA2024 and AA2024 / AA6082 Using a Spiral Slit and High Energy Synchrotron Radiation
Authors: Martins René V. , Honkimäki Veijo
Published: March 2009

The strain and phase distributions in friction stir welds (FSW) of AA2024-T3 to
AA2024-T3 and AA2024-T3 to AA6082-T6 are investigated non-destructively. The measurements are performed using a novel depth resolved strain and phase mapping technique. The technique is based on the use of a focussed high energy synchrotron beam, a novel spiral slit system, and an area detector system. The strain scans across the dissimilar FSW exhibit a strong asymmetry in particular for the longitudinal strain component. A depth resolved strain mapping across the weld
shows for the dominant longitudinal strain component variations in depth, especially on the AA6082 side of the dissimilar weld. The variations are significantlty weaker in the AA2024 / AA2024 weld. Results from the strain measurements are related to the depth resolved map of the material distribution in the weld zone.
Influence of Shot Peening on Fatigue Properties in Ultra-High Strength Steels
Authors: Gao Yu Kui , Wu Xue Ren , Lu Feng , Yao Mei , Yan Qingxian
Published: March 2009

The characteristics of compressive residual stress fields induced by shot
peening in 40CrNi2Si2MoVA, 16Co14Ni10Cr2Mo, 30CrMnSiNi2A and 0Cr13Ni8Mo2Al ultra-high strength steels, which are used widely in aeronautical
industry were investigated, and the change of surface integrity including surface
residual stress, surface roughness as well as its effects on fatigue properties were
investigated. The results show that the fatigue limits of ultra-high strength steels can
be increased by shot peening because the surface integrity can be ameliorated by shot peening, and that for a given steel there is a appropriate peening intensity under which the fatigue property of this steel is optimum. Finally, a judgement for the optimization condition of shot peening process is proposed based on a theory of micro-meso processes of fatigue crack initiation and experimental results. The technique should be considered to be optimum, if the fatigue crack source of shot peened specimen has been moved to the internal matrix metal region beneath the hardened layer; and its apparent fatigue limit has been improved and got to a value, which is near to that predicted according to the concept of surface/internal fatigue limit.
Non-Homogenous Precipitation Annealing of Maraging Steels
Authors: Grum Janez , Zupančič Martin
Published: March 2009

Nickel maraging steels in the as-delivered state show a microstructure consisting primarily of oversaturated lath martensite. The final mechanical properties are achieved with precipitation annealing, during which the dissolved alloying elements start to precipitate. The newly-formed precipitated phases efficiently hinder shifts of dislocations, which results in considerable changes of the mechanical properties. Strength and hardness thus essentially increase whereas the material shows a relatively high fracture toughness. The precipitated phases formed during precipitation annealing also cause some distortion of a workpiece and transformational residual stresses on the micro and macro scales. Linear strains after precipitation annealing range from -0.05% to -0.1% and depend primarily on temperature/time conditions during the precipitation process. The non-homogenous annealing such as laser annealing produces temperature-induced residual stresses which are combined with transformational stresses. These stresses are expected to be lower and much more different than the stresses occuring in comparable classical heat-treated steels, however they cannot be neglected due to the exceptional performance of maraging steels and also their employment with high-demanding products. The results of the residual stress measurements after laser-induced and classical heat treatments of Ni-Co-Mo maraging steel with 12% nickel are presented.
Residual Stress Analysis of Thermal Sprayed Molybdenum Deposit
Authors: Li L. , Vaidya A. , Streibl T. , Sampath S. , Gouldstone A. , Luzin Vladimir , Prask Henry
Published: March 2009

Thermal spray is a well-established, versatile method of producing protective and functional coatings. As with most thin- or thick-film structures, residual stresses developed during processing play an important role in determining the performance and life of sprayed coatings. Diffraction methods (X-ray or neutron) and in situ curvature measurement have been widely used to measure stresses nondestructively, yet results in coating stress measurements seen in the literatures are sometimes ambiguous or conflicting. This is due not only to the experimental error associated with the measurement and simplifying assumptions, but also the complexity and heterogeneity of the coating structure. During deposition, molten, semi-molten or solid particles successively impinge onto a substrate surface, thus forming a layered structure comprised of ‘splats,’ separated by interfaces, cracks and pores. In this study, X-ray micro-diffraction with a 2-D detector has been used to determine the stress magnitude of both splats and coatings on substrates. Neutron diffraction stress measurements have been made through the entire coating thickness. The process of depositing and cooling has been monitored by in situ curvature measurement. Micro- and macro stresses have been examined. The relation between process and splat and coating residual stresses has been evaluated and interpreted by recourse to microstructural and morphological observations under SEM. This study bridges the behaviors of microscopic single splats and macroscopic coatings, hence helps to fundamentally understand the stress generation during thermal spray process.
Sensitivity of a Rotating Beam Sensor for Stress Evaluation in Aluminium Thin Films
Authors: dos Santos J.M.M. , Pina J.C.P. , Batista António Castanhola , Horsfall Alton B. , Wang Kai , Wright Nicolas G. , Soare S.M. , Bull S.J. , O'Neill Anthony G. , Terry J.G. , Walton Anthony J. , Gundlach A.M. , Stevenson J.T.M.
Published: March 2009

The evaluation of stress in sub-micron tracks is critical for the microelectronics industry and there is a need for new methods of measurement. This paper advocates the use of a rotating beam sensor structure which can be fabricated on the wafer along side electronic devices and used to monitor stress generation and relaxation as a function of processing. The rotation can be observed with a reflected light microscope and correlated to the actual stress level. Several samples, assputtered and sintered, were prepared with the aim of having different residual stress states. X-ray diffraction with a low incident angle geometry, was used to evaluate the residual stresses on the aluminum layer. Computer simulations using ANSYS were also performed in order to correlate the sensor rotation with the experimental stress values. It was observed that the extrinsic stress from the
mismatch in expansion coefficients between the aluminum layer and the silicon substrate dominates over the compressive stress from the sputter growth. Sintering the layers at temperatures above 150°C reduces this compressive stress due to the action of creep. The calibration of the rotation of the device with the direct measurements of the X-ray diffraction shows that the sensor has a resolution better than 2.8 MPa.
Delamination and Buckling Induced by Compressive Strain in Metal Thin Films
Authors: Shen Yao Gen
Published: March 2009

The pattern formation during delamination and buckling in sputter-deposited tungsten thin films under large compressive stresses was investigated. The films were analyzed in situ by a cantilever beam technique, and ex situ by atomic force microscopy (AFM) and focused ion beam. Depending on the magnitude of compressive strain in thin films, different types of buckling patterns were observed. For stresses above a critical value, there was a regime of steady growth in which the
incipient blister evolves into a regular sinusoidal-like propagation. At higher strains, the sinusoidallike wrinkles were developed with constant widths and wavelengths. Some of the wrinkles bifurcated to form branches. With further increase in stress the complicated buckling patches were formed with many irregular lobes. These types of pattern formation have been supported by elastic energy calculations.
Evaluation of Corrosion Resistance of Multi-Layered Ti/Glass-Ceramic Interfaces by Electrochemical Impedance Spectroscopy
Authors: Avila Edith Ariza , Rocha L.A.
Published: March 2009

Practical applications of metal/ceramic joints can be found in the biomedical field regarding the encapsulation of implantable telemetric devices, the fabrication of crowns and bridges for dental restoration, or in the production of drug delivery systems, biomedical sensors and electrodes. Most of metal/ceramic joints are produced by the active metal brazing technique, which originates a multi-layered interface which should be able of accommodating the abrupt electronic, crystallographic, chemical, mechanical and thermo-mechanical discontinuity that characterize these systems. Additionally, when considering biomedical applications, corrosion resistance becomes of prime importance. In this work, the corrosion resistance of Ti/glass-ceramic interfaces obtained by active metal brazing was evaluated by electrochemical impedance spectroscopy (EIS) tests. The electrochemical behaviour of the interface was monitored, as a function of time, in a simulated physiological solution at room temperature. In order to evaluate the contribution of each layer and galvanic interactions between them, to the degradation mechanism of the interface, individual samples, representative of reaction layers present at the interface, were fabricated and electrochemically tested. Results show that the corrosion behaviour, of the whole interface was strongly influenced by the chemical composition of its constitutive layers. Thus, layers containing high contents of both titanium and silver showed a polarisation resistance increase with the immersion time, as a result of the formation of a thermodynamically stable passive film. On the other hand, the copper rich layer, appears to be the main responsible for the interface degradation. In fact, for high immersion times, an instable passive film is formed and, as a consequence, large amounts of copper are released. Galvanic interactions between the copper and the silver rich layers where also identified.
Micro-Structural Characterization and Stress-Corrosion Cracking Behavior of a FGM Glass-Based Coating on Ti6Al4V for Biomedical Applications
Authors: Pavón J. , Caillate M. , Jiménez-Piqué Emilio , Anglada Marc , López-Esteban S. , Saiz Eduardo , Tomsia Antoni P.
Published: March 2009

Microstructural and stress-corrosion cracking characterization of two glass-based coatings on Ti6Al4V with different SiO2 content (61% and 64% of SiO2) have been investigated in this work. These coatings belong to the SiO2-CaO-MgO-Na2O-K2O-P2O5 system and were obtained using a simple enamelling technique. They will be used as the first layer of the bioactive FGM coating. Microstructural characterization performed in the coatings by SEM shows the separation of the sintered glass particles after acid etching. The XRD integration method shows that the percentage of the crystalline phase (2.4CaO•0.6Na2O•P2O5) due to the partial devitrification is between 3-16 % vol. Mechanical characterization was made using Vickers and Hertzian indentation. Both coatings were sensitive to Vickers indentation subcritical crack growth with longer crack lengths for the smaller SiO2 content. This coating was also more sensitive to stress-corrosion “ring” cracking by Hertzian indentation. These two results are related with the larger residual stresses due to the thermal expansion mismatch.
Indentation of AlN/CrN Multilayers from Room Temperature to 400 °C
Authors: Giuliani F. , Goruppa A. , Lloyd S.J. , Teer Dennis , Clegg W.J.
Published: March 2009

Observations elsewhere have shown that multilayer structures with layers ~10 nm thick can be harder than monolithic ones. Here we see whether these effects can be observed at high temperatures and investigate the effect of temperature on the manner of deformation. The hardness of an AlN/CrN multilayer structure with a range of wavelengths from 6-200 nm has been measured at temperatures from room temperature to 400 oC. The changes in hardness have been related to the deformation behaviour observed by cross-sectional transmission electron microscopy and atomic force microscopy. These observations suggest that the mechanical properties of the coatings are dominated by the refinement in the columnar microstructure rather than directly by an effect of the layer interfaces on dislocation motion.
Numerical Simulation of Laser Induced Modification Processes of Ceramic Substrates
Authors: Rohde M. , Baldus O. , Dimitrova D. , Schreck S.
Published: March 2009

Laser supported processes can be used to modify the electrical and thermal properties of ceramic substrates locally. These processes are characterised by a strong thermal interaction between the laser beam and the ceramic surface which leads to localised melting. During the dynamic melting process an additive material is injected into the melt pool in order to modify the physical properties. The heat and mass transfer during this dynamic melting and solidification process has been studied numerically in order to identify the dominant process parameters. Simulation tools based on a finite volume method have been developed to describe the heat transfer, fluid flow and the phase change during the melting and solidification of the ceramic. The results of the calculation have been validated against experimental results.
Regularities of Composite Materials with Micrograded Grain Structure Formation
Authors: Kurbatkina V.V. , Levashov E.A.
Published: March 2009

Composite carbide materials in Ti-C, Ti-Nb-C, Ti-Zr-C systems were produced by combustion synthesis using the force SHS-pressing technology and investigated. Composition and structure of the synthesis products before and after annealing at 850oC, 1 hour were studied using optical and SEM, X-ray diffraction and Auger Electron Spectroscopy. It was established that SHSproducts consist of two main phases: TiC0.6+β-Ti, (Ti,Nb)C1-х + β-(Ti,Nb), (Ti,Zr)C 1-х + β-(Ti,Zr). Structure of these composite materials presented by carbide phase with a grain size varying 4-8 µm, and surrounded intergranular thin layer of β-Ti solid solution with width less than 1.5 µm. Composition and structure of carbide grains and intergranular phase just after combustion process is not equilibrium: supersaturated solid solutions are formed because of high temperature gradient and combustion velocity. Annealing results in an equalization of the solid solution composition. Carbide grains content precipitations sized 20-200 nm based on solid solution (Me-Ti). Two possible schemes of concentration separation of supersaturated solid solution were discussed: (Ti, Nb)x+yC = (Ti, Nb)xC 1-х + y(Nb-Ti) and (Ti, Zr)x+y C = (Ti, Zr)xC1-х + y(Ti-Zr). Lattice parameter of the intraganular phase differs from the matrix ones. Graded distribution of Nb and Zr alloying elements inside the carbide grains was observed. The developed composite materials strengthened by nano- or microsized particles are attractive for high-temperature applications.
Optimisation of FGM TBC and Their Thermal Cycling Stability
Authors: Gasik Michael M. , Kawasaki Akira , Kang Y.S.
Published: March 2009

Application of FGM concept for thermal barrier coatings (TBC) provides a superior thermal stress relaxation over homogeneous or duplex coatings. It was demonstrated that FGM TBC have better oxidation resistance and longer lifetime during test conditions. In this work, new FGM TBC system was designed using high-velocity oxygen flame (HVOF) coating process. After coatings optimisation, coating layer was subjected to a hot burner test for thermal fatigue cycling with increasing heat load. It was found that FGM TBC has successfully withstood thermal cycling and prevented visible delamination or transverse cracks. New coating design may give an opportunity to develop a cost-effective FGM TBC system for gas turbine applications.
Control of Optical Gain in the Active Region of Quantum Cascade Laser by Strong Perpendicular Magnetic Field
Authors: Radovanović J. , Milanović V. , Ikonić Z. , Indjin D.
Published: March 2009

The optical gain in the active region of quantum cascade laser in an external magnetic field is analyzed. When the magnetic field is applied in the direction perpendicular to the plane of the layers, electron dispersion is broken into series of discrete Landau levels. This additional confinement strongly modifies the lifetime of electrons in the upper state of the laser transition, which is controlled by electron-phonon scattering. Landau levels are magnetically tuneable and, depending on their configuration, phonon emission is either inhibited or resonantly enhanced. This
translates into a strong modulation of the population inversion, and consequently of the optical gain by varying the magnetic field. Numerical results are presented for a structure previously considered by Smirnov et al. [Phys. Rev B 66 (2002) 125317] which is designed to emit radiation at λ~11.4µm, with the magnetic field varied in the range 10-60T. The effects of band nonparabolicity are taken into account in this model.
Synthesis and Characterization of Ammonium Decavanadate (V)
Authors: Todorović M.R. , Mioč U.B. , Holclajtner-Antunović I. , Šegan D.
Published: March 2009

It is known that various polyoxovanadates interact specifically with enzymes, which is the main way of their biochemical activity. Therefore we have synthesized ammonium decavanadate, (NH4)6V10O28·6H2O. The novel compound was characterized by elemental and thermal analysis, X-ray powder and single crystal diffraction and IR and Raman spectroscopy. Its conductive properties have been studied, too. The spectroscopic analysis has shown the presence of hydrogen bonds of different strengths. In order to improve the biochemical activity of this compound and having in mind the presence of strong hydrogen bonds, we essayed the synthesis of complex of polyoxovanadate with alanine. The obtained product was characterized by the mentioned methods.
Investigation of Thermal Stability of Zn(II), Pt(II) and Pd(II) Complexes with (E)-2-oxo-2-{N'-[1-(pyridin-2-yl)ethylidene]hydrazino}acetamide
Authors: Todorović Tamara R. , Andjelković K.K. , Sladić D.M. , Jeremić D.A. , Minić D.
Published: March 2009

Thermal stability of neutral Zn(II), Pd(II) and Pt(II) complexes of formulae
[Zn(apsox)2]·3H2O and [M(apsox)Cl] (M=Pd(II), Pt(II), HL=(E)-2-oxo-2-{N ’-[1-(pyridin-2- yl)ethylidene]hydrazino}acetamide) were studied. The results of DSC and TG analyses within the temperature range from 20 to 600 °C in nitrogen atmosphere showed that the loss of crystal water represents the first step during decomposition of the octahedral Zn(II) complex followed by structural rearrangement of its anhydrous form. After that the complex remained stable to about 330 °C. Different from neutral square-planar Pd(II) and Pt(II) complexes, a satisfactory resolution of the peaks in DSC of the Zn(II) complex enabled determination of the activation energies of its structural transformation and thermal degradation.
Synthesis and Characterization of Biphasic Calcium Phosphate/ Poly-(DL-Lactide-Co-Glycolide) Biocomposite
Authors: Radić M. , Ignjatović N. , Nedić Zoran , Mitrić M. , Miličević Dejan , Uskokovic Dragan P.
Published: March 2009

In this paper we report the results on synthesis of a composite biomaterial based on biphasic calcium phosphate (BCP) and poly-(DL-lactide-co-glycolide) (DLPLG). Besides, we have investigated the influence of new synthesis method on the structure and characteristics of the composite. The synthesis of biphasic calcium phosphate from Ca(NO3)2 x 4H2O and (NH4)3 PO4 in alkali environment was performed by means of precipitation technique. Composite material BCP/DLPLG was first prepared from commercial granules using chemical methods. Powdered polymer DLPLG was then homogenized at appropriate ratio with addition of biphasic calcium phosphate into the suspension. All samples were characterized by DSC, IR, X-Ray and SEM techniques.
Modeling Texture, Twinning and Hardening Evolution during Deformation of Hexagonal Materials
Authors: Tomé Carlos , Kaschner George C.
Published: March 2009

Hexagonal materials deform plastically by activating diverse slip and twinning modes. The activation of such modes depends on their relative critical stresses, function of temperature and strain rate, and the orientation of the crystals with respect to the loading direction. For a constitutive description of these materials to be reliable, it has to account for texture evolution associated with twin reorientation, and for the effect of the twin barriers on dislocation propagation and on the stress-strain response. In this work we introduce a model for twinning which accounts explicitly for the composite character of the grain, formed by a matrix with embedded twin lamellae which evolve with deformation. Texture evolution takes place through reorientation due to slip and twinning. The role of the twins as barriers to dislocations is explicitly incorporated into the hardening description via a directional Hall-Petch mechanism. We apply this model to the interpretation of compression experiments both, monotonic and changing the loading direction, done in rolled Zr at 76K.
Effect of the Strain Reversal on Grain Boundary Character and Substructure Development on a Hot Worked Austenitic Stainless Steel
Authors: Jorge-Badiola D. , Iza-Mendia Amaia , Gutiérrez Isabel
Published: March 2009

A combination of monotonic and reverse tests has been carried out in order to assess the strain path effects on an austenitic stainless steel hot deformed by torsion. Microstructural results have been obtained by EBSD. The misorientation average parameter measured at different step size scans, the Kernel parameter and the orientation spread average parameter, provide a picture of the in-grain curvature developed during the different strain paths. The results show that these parameters are sensitive to the strain path.
Analysis of Intragranular Misorientation Related to Deformation in an Al-Mg-Mn Alloy
Authors: Takayama Yoshimasa , Szpunar Jerzy A. , Kato Hajime
Published: March 2009

Intragranular misorientation reflects strain generated during deformation with dislocation glide. The SEM/EBSP (scanning electron microscope/ electron back scatter diffraction pattern) technique provides is “kernel average misorientation (KAM)” as the most appropriate quantity to evaluate the strain or the stored energy for a given point. The KAM is defined for a given point as the average misorientation of that point with all of its neighbors. In the present paper two analyses of the intragranular misorientation using the SEM/EBSP technique for a cyclic deformation at room temperature and a high temperature deformation in an Al-Mg-Mn alloy are reviewed.