bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Management versus Full Isolation: Trade Off in Packaging Technologies of Modern SiC Diodes
Authors: Gerlach Rolf , Rupp Roland , Türkes Peter , Otremba Ralf
Published: March 2011

In this paper we compare the thermal behavior of identical SiC Schottky diodes mounted in i) a standard TO220 package (TO220) with non-isolated backside applying standard soft solder and diffusion solder die attach with ii) a so called FULLPAK TO220 package (TO220FP, only diffusion soldering). Depending on the solder technique the heat transport from the junction area of the SiC Schottky diode to the heat sink or to the package backside is improved for the diodes mounted via diffusion solder. For small chips this holds even for TO220FP in comparison to TO220 with standard solder. Simulations of the vertical temperature distribution after electrically heating with a half sine wave for 10ms up to 190W show a decrease of the maximal junction temperature of the SiC Schottky diode from TJ=260 °C to TJ=180 °C if the diffusion solder is used independent from the package type.
An All Silicon Carbide High Temperature (450+ °C) High Voltage Gain AC Coupled Differential Amplifier
Authors: Yang Jie , Fraley John , Western Bryon , Schupbach Marcelo , Lostetter Alexander B.
Published: March 2011

APEI, Inc. designed, fabricated and tested a high gain AC coupled differential amplifier based on a custom-built silicon carbide (SiC) vertical junction field effect transistor (VJFET). This SiC differential amplifier is capable of extreme temperature operation up to 450 °C, at which a high differential voltage gain of more than 47 dB is maintained. This high gain AC coupled differential amplifier can be integrated with high temperature sensors that deliver weak AC output signals to improve signal quality and noise immunity.
Chloride Based CVD of 3C-SiC on (0001) α-SiC Substrates
Authors: Henry Anne , Leone Stefano , Beyer Franziska Christine , Andersson Sven , Kordina Olof , Janzén Erik
Published: March 2011

A chloride-based chemical-vapor-deposition (CVD) process has been successfully used to grow very high quality 3C-SiC epitaxial layers on on-axis α-SiC substrates. An accurate process parameters study was performed testing the effect of temperature, in situ surface preparation, precursor ratios, nitrogen addition, and substrate polytype and polarity. The 3C layers deposited showed to be largely single-domain material of very high purity and of excellent electrical characteristics. A growth rate of up to 10 µm/h and a low background doping enable deposition of epitaxial layers suitable for MOSFET devices.
Study on the Feasibility of SiC Bandgap Voltage Reference for High Temperature Applications
Authors: Banu Viorel , Godignon Philippe , Jordá Xavier , Alexandru Mihaela , Millan José
Published: March 2011

This work demonstrates that a stable voltage reference with temperature, in the 25°C-300°C range is possible using SiC bipolar diodes. In a previous work, we have been demonstrated both theoretical and experimentally, the feasibility of SiC bandgap voltage reference using SiC Schottky diodes [1]. The present work completes the investigation on SiC bandgap reference by the using of SiC bipolar diodes. Simulated and experimental results for two different SiC devices: Schottky and bipolar diodes showed that the principles that govern the bandgap voltage references for Si are also valid for the SiC. A comparison between the output voltage levels of the two types of bandgap reference is also presented.
A Molded Package Optimized for High Voltage SiC-Devices
Authors: Dohnke Karl Otto , Bartsch Wolfgang , Schörner Reinhold , Van Weelden T.
Published: March 2011

We present first results on power cycling of 6.5 kV SiC PiN-diodes mounted into a molded package. The geometry of this lateral package was designed to fulfill the specifications of the electrical isolation and the creepage distances in the high voltage region of 6.5 kV. To evaluate the suitability of this package we used high voltage SiC PiN-diodes. The diodes were soldered onto a copper lead frame, wire bonded and covered by molding compound. The packaged diodes were characterized by electrical measurements before and during a power cycling test with a temperature swing of 90 K. These results showed long term stable behavior of the I-V characteristics of the diodes as well as the suitability of the package for high temperature and high voltage application of SiC devices.
Local Electrical Properties of the 4H-SiC(0001)/Graphene Interface
Authors: Sonde Sushant , Vecchio Carmelo , Giannazzo Filippo , Yakimova Rositza , Rimini Emanuele , Raineri Vito
Published: March 2011

Local current transport across graphene/4H-SiC was studied with nanometric scale lateral resolution by Scanning Current Spectroscopy on both graphene grown epitaxially on 4H-SiC(0001) (EG-SiC) and graphene exfoliated from highly oriented pyrolitic graphite and deposited on 4H-SiC(0001) (DG-SiC). The study revealed that the Schottky barrier height (SBH) of EG/4H-SiC(0001) is lowered by ~0.49eV. This is explained in terms of Fermi-level pinning above the Dirac point in EG due to the presence of positively charged states at the interface between Si face of 4H-SiC and carbon-rich buffer layer. Furthermore, Scanning Capacitance Spectroscopy based method allowed evaluating local electron mean free path (lgr) in graphene. lgr in EG-SiC was observed to be, on average, ~0.4 times that in DG-SiC and exhibited large point-to-point variations due to presence of laterally homogeneous positively charged buffer layer at the interface. However, lgr in graphene on SiC was observed to be larger than on standard SiO2 samples (DG-SiO2), which is explained by better dielectric screening of charged impurities and lower surface polar phonon scattering at the graphene/substrate interface.
Structural Investigations of a Sputtered Intermediate Carbonization Layer for 3C-SiC on (111) and (110) Si Substrates
Authors: Huguenin-Love James , Soukup Rodney J. , Ianno Ned J. , Lauer Noel T.
Published: March 2011

Thin SiC buffer layers have been grown by sputtering a graphite C target onto both (111) and (110) Si substrates. Converting the graphitic C into SiC is highly temperature dependent and relies on free silicon atoms that sublime from voids in the substrate at higher temperatures. Morphological and structural investigations were performed by Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffraction (XRD).
Cellular Interactions on Epitaxial Graphene on SiC (0001) Substrates
Authors: Oliveros A. , Coletti Camilla , Frewin Christopher L. , Locke Christopher , Starke Ulrich , Saddow Stephen E.
Published: March 2011

An ever-increasing demand for biocompatible materials provides motivation for the development of advanced materials for challenging applications ranging from disease detection to organ function restoration. Carbon-based materials are considered promising candidates because they combine good biocompatibility with high chemical resistance. In this work we present an initial assessment of the biocompatibility of epitaxial graphene on 6H-SiC(0001). We have analyzed the interaction of HaCaT (human keratinocyte) cells on epitaxial graphene and compared it with that on bare 6H-SiC(0001). We have found that for both graphene and 6H-SiC there is evidence of cell-cell and cell substrate interaction which is normally an indication of the biocompatibility of the material.
Epitaxial Growth on 4H-SiC on-Axis, 0.5°, 1.25°, 2°, 4°, 8° Off-Axis Substrates – Defects Analysis and Reduction
Authors: Kościewicz Kinga , Strupiński Wlodek , Teklinska Dominika , Mazur Krystyna , Tokarczyk Mateusz , Kowalski Grzegorz , Olszyna Andrzej Roman
Published: March 2011

A good selection of growth parameters (in-situ etching, C/Si ratio, growth rate) enables obtaining of ~1nm high steps of epitaxial layers, which are comparable to the size of an elementary cell (8°off-axis) and achieve the density of BPD=8•103/cm2. Due to crystallization on substrates with low misorientation (<2°off-axis) it is possible to obtain epitaxial layers substantially lacking in BPD dislocations. However, a slightly more developed surface with Ra=1-2.5nm (1.25°, 2°off-axis) characterizes these layers. By lowering the C/Si ratio, morphology of layers crystallized on substrates with low misorientation was improved. Extending growth rate improved both the crystallographic quality of the grown layers and their polytype stability. Nevertheless, growth without BPDs, also referred to as the homogeneous (4H) polytypic growth on 4H-SiC on-axis substrates, is the most efficient way of defect elimination.
Investigation of the Growth of 3C-SiC on Si by Vapor-Liquid-Solid ( VLS ) Transport
Authors: Berckmans Stéphane , Auvray Laurent , Ferro Gabriel , Cauwet François , Carole Davy , Soulière Véronique , Viala Jean Claude , Collard Emmanuel , Quoirin Jean Baptiste , Brylinski Christian
Published: March 2011

In this work, the growth by Vapour-Liquid-Solid (VLS) mechanism of 3C-SiC on silicon substrate is reported. Firstly, a germanium layer is deposited on the substrate. Then the temperature of the sample is increased above Ge melting point in order to form a SiGe liquid phase by reaction with the substrate. Upon reaching the target temperature (1100-1300°C) the VLS growth starts with the injection of propane in the reactor. Both Raman spectrometry and X-Ray diffraction analyses evidenced the formation of 3C-SiC on every sample. However, this SiC deposit, a few micrometers thick, is always found to be polycrystalline though textured. In parallel, the presence of an epitaxial Si-Ge alloy, whose composition depends on the growth temperature, was systematically detected between Si and SiC.
Stress Analysis by Kossel Microdiffraction on a Nickel-Based Single Crystal Superalloy during an In Situ Tensile Test – Comparison with Classical X-Ray Diffraction
Authors: Bouscaud Denis , Pesci Raphaël , Berveiller Sophie , Patoor Etienne
Published: March 2011

A Kossel microdiffraction experimental set up is under development inside a Scanning Electron Microscope (SEM) in order to determine the crystallographic orientation as well as the inter- and intragranular strains and stresses. An area of about one cubic micrometer can be analysed using the microscope probe, which enables to study different kinds of elements such as a grain boundary, a crack, a microelectronic component, etc. The diffraction pattern is recorded by a high resolution Charge-Coupled Device (CCD) camera. The crystallographic orientation, the lattice parameters and the elastic strain tensor of the probed area are deduced from the pattern indexation using a homemade software. The purpose of this paper is to report some results achieved up to now to estimate the reliability of the Kossel microdiffraction technique.
Localization of Stresses in Polycrystalline Grains Measured by Neutron Diffraction and Predicted by Self-Consistent Model
Authors: Gaj Anita , le Joncour Lea , Baczmanski Andrzej , Wroński Sebastian , Panicaud Benoit , François Manuel , Braham Chedly , Paradowska Anna Maria
Published: March 2011

Time of flight neutron diffraction method was applied to measure elastic lattice strains in austenitic steel during "in situ" tensile test. Comparing experimental data with self-consistent model, the critical resolved shear stress and hardening parameters were determined for polycrystalline grains. The result allowed us to determine the main component of the stress localization tensor, relating the rate of grain stress with the applied macrostress rate. The evolution of concentration tensor in function of the applied macrostress was analyzed. Finally, the load transfer between grains during yielding of the sample was studied.
Influence of Surface Roughness on Evaluation of Stress Gradients in Coatings
Authors: Benediktovich Andrey , Guerault Hugues , Feranchuk Ilya , Uglov V. , Ulyanenkov Alex
Published: March 2011

Roughness influence on the residual stress gradient evaluation in the case of a grazing incidence X-ray diffraction setup is considered. In this geometry the surface roughness changes essentially the X-ray wave fields of the transmitted and diffracted beams inside the coatings and subsurface regions of bulk samples, and thus influences the refractive properties of the investigated sample area. In turn, the change in the refraction index enforces the re-scale of the informational depth and, consequently, the evaluated stress depth profile. The diffracted amplitude from the crystalline grain located beneath the surface is calculated. The surface roughness is shown to contribute into reconstruction of the real stress gradient profile of the coating.
Thermal Residual Stress Relaxation in Sputtered ZnO Film on (100) Si Substrate Studied In Situ by Synchrotron X-Ray Diffraction
Authors: Krauss Christopher , Geandier Guillaume , Conchon Florine , Renault Pierre Olivier , Le Bourhis Eric , Benedetto Alessandro , Grachev Sergey.Y. , Goudeau Philippe , Barthel Etienne
Published: March 2011

Residual stress relaxation in sputtered ZnO films has been studied in-situ by synchrotron x-ray diffraction. The films deposited on (001) Si substrates were thermally treated from 25°C to 700°C. X-ray diffraction 2D patterns were captured continuously during the heating, plateau and cooling ramps. The corrections carried out for compensating the furnace drift are discussed. We first observe an increase of the intrinsic compressive stresses before stress relaxation starts to operate around 370°C. Then, thermal contraction upon cooling dominates so that overall, the large initial compressive film stresses turn to tensile after thermal treatment. The overall behaviour is discussed in terms of structural changes induced by the heat treatment.
Residual Stress Measurement in Coated Plates Using Layer Growing/ Removing Methods: 100Th Anniversary of the Publication of Stoney’s Paper “the Tension of Metallic Films Deposited by Electrolysis”
Authors: Kõo Jakub , Valgur Jaak
Published: March 2011

In connection with the 100th anniversary of Stoney’s equations, some historical remarks are made with respect to the development of these equations. As an example of the extension of Stoney’s equations, a unique algorithm of the layer growing/removing methods is presented for de­termination of residual stresses in isotropic inhomogeneous coated plates. Using a computer pro­gram based on this algorithm, residual stresses are computed in the galvanic steel coating on the copper plate substrate.
Evaluation of Residual Stresses in Dissimilar Weld Joints
Authors: Bonaventur Alix , Ayrault Danièle , Montay Guillaume , Klosek Vincent
Published: March 2011

Dissimilar metal joints between pipes of ferritic and austenitic steels are present in primary coolant circuit of pressurized water reactors. Over the last years in particular in USA and Japan, stress corrosion cracks, often associated with weld repairs, have been observed for some dissimilar welds made with an Inconel filler metal. The integrity of this type of components is thus a major safety issue. In this context, the goal of this work is to evaluate the welding residual stresses field for a dissimilar weld joint. A representative bi-metallic tubular weld joint was fabricated and residual stresses profiles in the different weld zones were evaluated by means of the hole drilling and neutron diffraction methods.
Residual Stresses in Austenitic Steel during Plastic Deformation and Recovery Processes
Authors: Wawszczak Roman , Baczmanski Andrzej , Braham Chedly , Seiler Wilfrid , Wróbel Mirosław , Wierzbanowski Krzysztof
Published: March 2011

X-ray diffraction method was applied to measure residual stresses in deformed and annealed polycrystalline austenitic steel. An elastoplastic deformation model was used in analysis of experimental data. As the result, the orientation distribution function of grain stresses, created during elastoplastic deformation was determined and presented in the Euler space. An important decrease of the first and the second order residual stresses was observed during recovery process. It was found that the magnitude of the stresses decreases, while their distribution between different grain orientations remains almost unchanged.
Numerical Analysis of Laser Shock Peening as a Process for Generation of Compressive Residual Stresses in Open Hole Specimens
Authors: Ivetic Goran , Meneghin Ivan , Troiani Enrico
Published: March 2011

A numerical analysis of Laser Shock Peening (LSP) process is illustrated, applied to an open hole specimen. This specimen is representative of a section of an aircraft fuselage lap joint, typically prone to fatigue crack nucleation at the rivet holes. The effect of the residual stress field induced by LSP on the fatigue life of open hole specimens is investigated. The results show that significant compressive residual stresses can be introduced in fatigue sensitive areas using LSP, postponing fatigue crack nucleation.
Forging and Shot-Peening Contribution on Residual Stresses for a Textured Biphasic Titanium Alloy
Authors: Deleuze Camille , Fabre Agnès , Barrallier Laurent , Molinas Olivier
Published: March 2011

Residual stresses are to be determined to predict mechanical behaviour of vital parts in aircraft. This part constituted by Ti-10V-2Fe-3Al is analysed using x-ray diffraction (XRD). However, the broadening and sometime the disappearance of peaks involve a major difficulty to quantify the strains and the stresses which are close to the surface. In the current study, some investigations are conducted in order to understand the difficulties to evaluate stresses by XRD. The microstructure of samples is studied by taking into account the history of surface generation: after the forging and after the shot-peening process. Shot-peening induces a distortion of the primary phase α which is close to the surface. Different deformation rates introduced by forging process have generated a different organisation in the second phase constituted by α secondary and β. To complete the investigation, crystallographic textures are performed on α phase. The main difficulty in analysing when using XRD is due to the peak broadening. The conclusion of this study identifies three separate zones beneath the surface: where the stresses can be determined, it is possible to analyze it using different method of analysis with different levels of accuracy.
A Multi-Scale Study of Residual Stresses Created during the Cure Process of a Composite Tooling Material
Authors: Lacoste Emmanuel , Fréour Sylvain , Jacquemin Frédéric
Published: March 2011

This paper deals with the cure of an in-plane isotropic carbon-polymer tooling material, with a complex microstructure [1]. The Mori-Tanaka (MT) and Eshelby-Kröner self-consistent (EKSC) models are used in order to achieve a two-steps scale transition procedure, relating the microscopic properties of the material to their macroscopic counterparts. This procedure enables estimating the multi-scale mechanical states experienced by the material, i.e. the local (microscopic) stresses due to thermal and chemical shrinkage of the resin, along a typical, macroscopic stress-free, cure process. The influence of the chosen scale transition model on both the calculated effective properties of the material and its local stress states, is investigated. These results are a first step for investigating the service life fatigue of the material, as well as its failure behaviour.
Neutron Diffraction Analysis of Load Transfer in DP 600 Steel During In Situ Tensile Tests
Authors: Seefeldt Marc , Dillien Steven , Stuhr Uwe
Published: March 2011

The load transfer among ferrite orientations and between ferrite and martensite was analysed in DP 600 steel by means of neutron diffraction duringin situtensile tests on the multiple pulse overlap time-of-flight strain scanner POLDI. The material had 0.07 wt% C and a martensite volume fraction of 15%.In situtests were done in “Young” as well as in “Poisson setup”. The martensite phase could not be probed due to its low tetragonality. The curves of the lattice plane strains as a function of the externally applied macroscopic stress reveal (1) plastic relaxations of transformation and intergranular stresses in the compliant <100> oriented grains, and (2) a second inflection point in the fully plastic part indicating the onset of plastic deformation of the hard phase.
Simulation and Evaluation of Residual Stress in Bone at the Interface with Implant
Authors: Benmarouane Abdelilah , Shi Yeting , Mireux Bastien , Buslaps Thomas , Lodini Alain
Published: March 2011

The use of the implants has become current since 1930. With the improvement of technology, titanium alloy coated with nano-hydroxyapatite has been used in the medical field. As a long-term establishment is a meter of the therapeutic success, it is necessary to use biocompatible implants in order to have good mechanical and fracture resistance at the interface bone-implant. In orthopaedic surgery Titanium (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca10 (PO4)6 (OH)2, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface the new bone reconstituted after implantation must have the same mechanicals properties as the natural bone in order to accept the implant. Therefore we studied the residuals stresses of the new bone crystals reconstituted at the interface applying non destructive x-ray diffraction and using finite element analysis in order to compare the results.
Local Residual Stress Distributions Induced by Repeated Austenite-Martensite Transformation via Laser Surface Hardening of Steel AISI 4140
Authors: Kostov Vladimir , Gibmeier Jens , Wanner Alexander
Published: March 2011

The effects of laser surface hardening of steel samples on the microstructure and residual stresses were determined for single as well as multiple laser pulses. Samples made of steel grade AISI 4140 were hardened by means of a high-power diode laser (HPDL) system using either single or multiple laser pulses resulting in single as well as repeated austenite-martensite transformations. The hardening was carried out in a specially designed process chamber allowing laser surface treatment in inert atmosphere in order to avoid oxide scale formation. The residual stress distributions in lateral and in depth direction were analysed by means of X-ray diffraction for samples hardened by up to 27 laser pulses. Residual stress analyses were carried out by means of the sin²y- method. The results indicate the extension of the hardened zone in lateral and in depth direction with an increase in the number of applied laser pulses. This evolution is connected with significant changes in the local residual stress distributions.
Analysis of Residual Stress Induced by Hand Grinding Process
Authors: Youssef Sawsen , Calonne O. , Feulvarch Eric , Gilles P. , Hamdi Hédi
Published: March 2011

Grinding cup wheel is often used in the case of hand grinding which allows an important material removal rate but with secondary concern of surface integrity. Integrity is strongly affected by the process and consequently influences the surface behaviour in terms of resistivity to stress corrosion and crack initiation. This operation is difficult to master in terms of results on the surface and subsurface due to its manual nature. The paper presents results of an experimental study to investigate the residual stresses induced by this hand grinding process.
Depth and Lateral Variation of Machining-Induced Residual Stress for a Nickel Base Superalloy
Authors: Li Wei , Withers Philip J. , Preuss Michael , Shackleton Judith , Andrews Paul
Published: March 2011

This paper investigates the variation of residual stress with depth and radial location in a nickel base superalloy, RR1000, introduced by face finish turning. X-ray diffraction stress measurement has revealed that the hoop stress at the surface becomes less tensile towards the centre of the face, whilst the level of radial sub-surface compression increases. The unstrained lattice spacing d0 and the diffraction peak width (FWHM) were used to make inferences regarding the thermal excursion and the plastic work, respectively. It was found the increase in the compressive stress from the outer towards the inner radius was associated with an increase in thermal excursion.
Residual Stress in Tools and Components in Case of Thermo-Mechanical Metal Forming Processes
Authors: Grüning Alexander , Lebsanft Markus , Scholtes Berthold
Published: March 2011

Residual stresses play a key role in thermo-mechanically coupled forming processes for industrial mass production. They are an unavoidable consequence of the alternating inhomogeneous fields of temperature and mechanical stress developing in tools and components dependent on the process parameters applied. Because of their influence on the behavior of the components produced, a great interest exists to get reliable information about origin and distribution of the relevant residual stress fields and to understand the basic principles of their formation. In this paper the development of residual stress in tools (steel AISI H11) used for the thermo-mechanical forming operation of cylindrical flange shafts (steel SAE 6150) is outlined. The loading situation of the tool is simulated by thermal fatigue tests, providing information about cyclic stress and plastic deformation during the manufacturing process. Furthermore the residual stress states of the flange shafts manufactured are presented and discussed. Chip forming manufacturing operations are challenging tasks and tensile residual stresses can be avoided using adapted process parameters.
Residual Stress Distribution in Hardened Case Layer of Cr-Mo Steel after Carburizing and Quenching
Authors: Sakaida Yoshihisa , Yamashita Shohei , Manzanka Michiya
Published: March 2011

The hollow circular cylinder specimen of Cr-Mo steel with 0.20 mass% C was carburized in carrier gas and quenched in oil bath. After quenching, the surface residual stress distributions in the radial, axial and hoop directions of the specimen were measured experimentally by x-ray as a function of the distance from the carburized surface. The case depth of the quenched specimen was about 0.8 mm. Diffraction from Fe-211 by Cr-Kα radiation was used to minimize the effect of carbon content gradient on the nonlinearity of 2θ-sin2ψ, because effective x-ray penetration depth was about 5.8 μm at sin2ψ=0. The hardened case layer was gradually removed by electrolytic polishing. X-ray stress measurement was repeated on the polished surface from the carburized surface to the interior. The ψ-splitting was not observed on the carburized surface. The 2θ-sin2ψ diagrams were found to shift from low to high angles in inverse proportion to carbon content. The residual stresses in the hardened case layer were compressive. The maximum compressive residual stresses on the hollow circle and periphery surfaces were about −559 and −544 MPa at the depth of 0.2 and 0.3 mm, respectively. On the other hand, the tensile residual stress was not observed. The full widths at half-maximum intensity of Fe-211 diffraction peaks in the hardened case layer were wider than that of the interior of the specimen. Martensitic transformation of the carbon-rich layer leaded to the broadening of diffraction peaks. Therefore the interior of carburized specimen were deformed elastically to balance the existence of the surface compressive residual stresses.
Analysis of Residual Stress Development during Thermal Processing of AL-SI Alloys
Authors: Sadrossadat S. Mohsen , Peng Ru Lin , Johansson Sten
Published: March 2011

Residuals stresses can be present in almost every industrial component. Manufacturing processes such as casting, welding, and heat treatment are the most common causes of residual stresses. Thermal residual stresses could be developed in a component during heat treatment process as a result of non-uniform heating or cooling operations. In this study, experiments were carried out to develop insights into and understanding of the residual stresses that can arise during thermal treatments of Al-Si components. Due to the complexity of residual stresses analysis in real components, a common mixed-section casting was employed. In order to fulfill the requirements of performing different thermal treatments, a special cooling apparatus was designed and built. A number of the casting components of an Al-Si alloy were annealed for stress relief, and then removed from the furnace and cooled with different water flow rates. Then, the amount of accumulated residual stresses in the components was measured relaxation of stress using cutting. Thermal analysis and residual stress measurement for different thermal treatment regimes showed that by choosing a specific holding temperature before direct cooling, the value of residual stress increases linearly with flow rate of cooling. On the other hand, for a constant value of cooling water flow, ∆Tmaxand residual stress level decreases when the value of base temperature of furnace decreases. Moreover, the cutting method can be a suitable method for measuring thermal residual stresses in Al-Si components and thermal analysis is a powerful technique to predict residual stresses.
Residual Stresses in Multilayer Welds with Different Martensitic Transformation Temperatures Analyzed by High-Energy Synchrotron Diffraction
Authors: Kromm Arne , Kannengiesser Thomas , Altenkirch Jens , Gibmeier Jens
Published: March 2011

Low Transformation Temperature (LTT) alloys were developed in order to control the residual stress development by the martensitic phase transformation already during cooling of the weld metal. The positive effect of such LTT alloys on the mitigation of detrimental tensile residual stresses during welding has already been confirmed on the basis of individual laboratory tests. Within the current project it was experimentally investigated whether the phase transformation mechanisms are effective under increased restraint due to multi-pass welding of thicker specimens. The local residual stress depth distribution was analyzed non-destructively for V-type welds processed by arc welding using energy dispersive synchrotron X-ray diffraction (EDXRD). The use of high energy (20 keV to 150 keV) EDXRD allowed for the evaluation of diffraction spectra containing information of all contributing phases. As the investigated LTT alloy contains retained austenite after welding, this phase was also considered for stress analysis. The results show in particular how the constraining effect of increased thickness of the welded plates and additional deposited weld metal influences the level of the residual stresses in near weld surface areas. While the longitudinal residual stresses were reduced in general, in the transition zone from the weld to the heat-affected zone (HAZ) compressive residual stresses were found.
Residual Stress Measurement Of High Molecular Matter By Transmission X-Ray Diffraction
Authors: Kitamura Masashi , Masayuki Nishida , Takao Hanabusa
Published: March 2011

In this study, the residual stresses in high-density polyethylene (HDPE) were measured using an x-ray stress measurement technique. There have been few reports published of residual stress investigations in polymeric materials by x-ray stress measurements based on conventional x-ray reflection methods. There are two problems associated with this measurement. Firstly, the diffraction peaks of the polymer in the low 2q angle region and therefore the measurement accuracy for strains reduces. Secondly, the low 2q angle region makes it extremely difficult to use the sin2ψmethod. In the present study we tried to use a transmission method for measuring the residual stress in HDPE sample to resolve these problems. The HDPE sample is shaped into thin sheets which have the three kinds of crystallinity degrees. The measured data is fitted with a good linear regression line in a d-sin2ψdiagram and gradient of the regression line corresponded to the applied stress. On the other hand, the results of the residual stress measurement are deeply associated with degrees of the crystallinity in the HDPE material. The quantitative estimation of crystallinity degrees in the HDPE material was accomplished by a sink-float method. The residual stress distributions were discussed between micro-residual stresses in the crystal phase of HDPE with the amorphous phase of it. Finally, x-ray elastic constant (XEC) of HDPE was estimated and the Initial residual stresses were also measured by use of this XEC parameter.
Stress in Aluminium Alloys Measured Using Göbel Mirror as a Primary Beam Optics of X-Ray Diffractometer
Authors: Marciszko Marianna , Baczmanski Andrzej , Zazi Nacer , Chopart Jean Paul , Lodini Alain , Wierzbanowski Krzysztof
Published: March 2011

Grazing incidence geometry, called MGID-sin2y, was applied to measure surface stresses in very thin layers (depth of a few mm) of Al-Mg alloy samples subjected to different thermal and mechanical treatments. The Göbel mirror was used to parallelize the incident X-ray beam. Perfect collimation of the beam significantly increases accuracy of determined peak position and consequently allows to measure low stresses in surface layers.
Neutron Surface Residual Stress Scanning Using Optimisation of a Si Bent Perfect Crystal Monochromator for Minimising Spurious Strains
Authors: Rebelo-Kornmeier Joana , Gibmeier Jens , Hofmann Michael , Wimpory Robert C.
Published: March 2011

For non destructive stress analysis of surface treated steel samples the application of laboratory X rays or high energy synchrotron radiation in reflection mode covers the region from some micrometers up to a depth of about 150 - 200 µm. To access depth regions deeper than 200 µm the incremental layer removal technique in combination with the repeated application of X‑ray stress analysis for the newly generated surfaces can be used. However, this procedure is destructive, laborious and furthermore, it has to be checked whether corrections have to be applied due to stress relaxation. By using neutron radiation penetration depths generally up to several millimetres can be achieved non destructively [1]. However neutron measurements are critical at the surface. When scanning a sample surface, aberration peak shifts caused by so called spurious strains arise due to the fact that the gauge volume defined by the primary and secondary optics is partially outside of the sample. These aberration peak shifts can be of the same order of magnitude as the peak shifts related to residual strains [2-6]. In this exemplary study it will be demonstrated that, by optimising the bending radius of a Si (400) monochromator, the spurious surface strains can be strongly reduced when compared to the values obtained with a traditional Ge (311) mosaic monochromator, even when the gauge volume is mainly out of the surface. The objective of the experiments is to find the optimal monochromator settings for the Si (400) monochromator at the STRESS-SPEC instrument at the research reactor FRM II, Munich, Germany. For the parametric studies a stress free steel sample of the fine grained construction steel, S690QL was used. The optimised conditions for the Si (400) monochromator that resulted from the systematic studies were applied to a shot peened plate of steel SAE 4140. The residual stress distribution is analysed by means of through surface strain scanning. The residual stress gradient obtained is in very good agreement with the well characterised residual stress depth profile obtained within a round robin test in the scope of the BRITE-EURAM-project ENSPED (European Network of Surface and Prestress Engineering and Design) [7]. The results indicated that surface residual stress profiles can be measured with neutrons up to 200 µm underneath the surface without time consuming and laborious surface effect corrections.
Influence of Grain-Matrix Interaction Intensity and Lattice Rotation Definition on Predicted Residual Stresses and Textures
Authors: Wronski Marcin , Wierzbanowski Krzysztof , Baczmanski Andrzej , Lipiński Paul , Bacroix Brigitte , Seiler Wilfrid , Lodini Alain
Published: March 2011

Formation of residual stresses and crystallographic textures during rolling have been studied using elasto-plastic deformation for polycrystalline material (Leffers-Wierzbanowski model). The rotation of grain crystal lattices is the basic mechanism of texture formation and anisotropic behavior of metals during plastic deformation. The classical definition of crystal lattice rotation leads in some cases to different texture predictions than the definition based on the orientation preservation of selected sample planes and/or directions (preservation condition). Also predicted residual stresses can be influenced by a choice of rotation definition. In the used deformation model of polycrystalline material, the intensity of grain-matrix interaction is described by the parameter L= aG, where G is shear modulus and a is elasto-plastic accommodation parameter. Model calculations have been done for different values of this parameter and for two definitions of lattice rotation. The predicted second order residual stresses and crystallographic textures for cold rolled ferrite steel are compared with experimental ones.
DECcalc - A Program for the Calculation of Diffraction Elastic Constants from Single Crystal Coefficients
Authors: Manns Thorsten , Scholtes Berthold
Published: March 2011

A Matlab based computer program was developed which gives the possibility to calculate the diffraction elastic constants (DEC) of macroscopically isotropic, single phase materials from their single crystal elastic constants. The proper function of the program was confirmed by means of results from literature. In almost all cases the results from the program DECcalc could reproduce the values and diagrams given in the appropriate publications. Discrepancies could always be assigned to the use of different single crystal coefficients.
Stress Analysis in UMo-Al Fuel Using X-Ray Diffraction
Authors: Kubler Regis , Barrallier Laurent , Valot Christophe , Palancher Hervé , Boquet Olivier
Published: March 2011

UMo-Al specimens are analyzed using X-ray diffraction techniques. One specimen was partially irradiated using a heavy ion beam127I. Another specimen was thermally annealed 2h at 400°C. Those treatments result in the formation of an interaction layer between UMo particles and Al matrix. UMo, Al and UAl3phases are identified in the treated specimen using X-ray diffraction. Only aluminium phase exhibits a crystallographic fiber texture, the other phases having an isotropic crystallographic texture. X-ray stress analyses are performed. After irradiation, stress analyses show that UMo phase is in a compressive stress state whereas the stress level in the formed UAl3in the interaction layer is not that high.
Determination of Residual Stresses After Laser Remelting of Flame Sprayed Fe-Ni-Co-Mo Coating
Authors: Bergant Zoran , Grum Janez
Published: March 2011

In this paper, the residual stresses on flat specimens, made from 12-nickel precipitation hardening maraging hot-working tool steel coated with Fe-Ni-Co-Mo and subsuquent laser remelted using Nd:YAG laser, were determined using the hole drilling method. In this newly proposed multi-step process for hot working tool steel reparation, the residual stresses are generated during each step by different physical mechanisms. The flame spraying is a highly productive technique to replace worn out material but with limited bonding to the substrate material. Subsequent laser remelting improves coating's bonding with substrate, coating's density and deoxidation to improve wear resistance, erosion and corrosion resistance of the flame sprayed coatings. After laser remelting, the tensile stresses in coatings slightly reduces or shifts into compressive which in turns improves the crack initiation resistance of the repaired surface of the thermomechanicaly loaded die casting tool.
Simulation and Measurement of Residual Stresses in a Type 316H Stain­less Steel Offset Repair in a Pipe Girth Weld
Authors: Hossain M.S. , Goudar D.M. , Truman Christopher E. , Smith David John
Published: March 2011

In common with all mechanical strain relief residual stress measurement methods, extra care must be taken when making measurements on components containing highly triaxial residual stress fields which are close to yield. The introduction of a free surface, created as part of the measurement procedure, can lead to plastic redistribution of the residual stress field. Usually, this is not accounted for in the elastic inversion algorithms of the experimental procedure. This paper demon­strates the usefulness and accuracy of deep-hole drilling (DHD) method [1] in a component predicted to contain a triaxial residual stress field. Previous measurements [2] are compared with the results of a DHD simulation on a type 316H stainless steel pipe containing a repair weld offset from an original girth weld. The influence of different material models was also studied.
Uncertainties in Triaxial Residual Stress Measurements
Authors: Goudar D.M. , Hossain M.S. , Truman Christopher E. , Kingston Ed J. , Smith David John
Published: March 2011

Residual stress measurement techniques using mechanical strain relaxation depend on a number of physical quantities and are therefore sensitive to errors associated with the measured data. The resulting stress uncertainties can easily become significant and compromise the usefulness of the results or lead to misinterpretation of the behaviour of the residual stress distributions. It is therefore essential to develop an error analysis procedure for the measurements undertaken. Error analysis procedures for the deep hole drilling (DHD) method are developed to consider triaxial residual stresses. A modified deep hole drilling method, called the incremental deep-hole drilling (iDHD), was applied to measure the near yield residual stress distributions in a cold water quenched aluminium 7010 alloy forged block. The experimental results are used to illustrate the errors.
Deformation Histories Relevant to Multipass Girth Welds: Temperature, Stress and Plastic Strain Histories
Authors: Mullins Jonathan , Gunnars Jens
Published: March 2011

Residual stresses predicted from welding simulations are known to be sensitive to the choice of material model. Recent work has shown large differences in the predicted residual stress profile when different types of hardening model are used (isotropic, kinematic or mixed models). More information is required regarding the exact deformation conditions that exist during welding. We consider finite element models of two multi-pass, stainless steel girth welds. Temperature, stress and plastic strain histories are recorded in the weld material and in the heat affected region (HAZ). Material in the weld and HAZ is observed to undergo three to five cycles of active plastic deformation followed by thermal cycling that is purely elastic. The stress state varies from biaxial compression to triaxial tension. These deformation histories are used as the basis for a discussion of the formulation of a suitable material testing schedule and subsequent constitutive modelling.
Microstructure and Performance of Surface Nanostructure 316L Stainless Steel Induced by Wire-Brushing Deformation
Authors: Zhu Ling , Fan Xin Min
Published: March 2011

Nanostructured surface layer was synthesized on 316L stainless steel by means of high-speed rotation wire-brushing deformation (HRWD). The refined microstructure features were systematically characterized by optical microscopy (OM), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) observations. Furthermore, the microhardness was examined by microhardness tester. After HRWD treatment, obvious grain refinement was observed and a nanocrystalline surface layer was formed on 316L stainless steel. It was found that a gradient microstructure with grain size from nanoscale to microscale was obtained along the depth of its surface layer. The thickness of the nanocrystalline surface layer varies from a few to about 20μm depending upon the treatment duration and compressive stress. The microhardness of nanostructured surface layer was enhanced significantly, and along the depth from the top surface, the microhardness in the surface gradually decreased to that of the matrix. Besides, the grain refinement mechanism and behaviors were discussed.
Numerical and Experimental Investigation of Strain Inhomogeneity during Cyclic Channel Die Compression
Authors: Shi Feng Jian , Wang Lei Gang , Lu Sheng , Huang Zhong Fu
Published: March 2011

Severe plastic deformation (SPD) can refine conventional coarse-grained materials to submicrometer or even nanometer level. In this paper, effective strain distribution was simulated by rigid-plastic finite element method (FEM) after multi-pass cyclic channel die compression (CCDC) by two different processing routes, and the Vickers microhardness was examined to verify the deformation distribution. The results show that large strain can be accumulated in the material by CCDC. The deformation distribution is non-uniform. Apart from the edges or corners of the specimen, the effective strain is higher in the central region and lower at the surrounding region. The effective strain gradient increases with the number of compression. The microhardness distribution features of two routes are in agreement with the simulation results of strain distribution. The microhardness increases globally with the number of compression and its distribution is inhomogeneous at the small and medium strain stage. But with the increasing of strain, the microhardness homogeneity is improved.
Microstructures and Mechanical Properties of Fcc Pure Metals with Different Stacking Fault Energies by Equal Channel Angular Pressing
Authors: Zhang Yue , Liu Jin Qiang , Wang Jing Tao , Wu Zhi Bin , Liu Fan
Published: March 2011

In the present work 99.98% commercial pure copper, 99.5% commercial pure nickel and 99.5% commercial pure aluminum were imposed on high strain levels of ~24, ~8 and ~44 by equal channel angular pressing (ECAP) via route Bc, respectively. Microstructures and mechanical properties are investigated by TEM observations, tensile tests and microhardness tests. It shows that grain sizes of pure copper, pure nickel and pure aluminum has been severed refined from several tens of microns into several hundreds of nanometers after ECAP processing, however, microstructure of copper are mainly consisted of equiaxed (sub) grains with illegible grains/ (sub) grains boundaries after processed by ECAP, while it is featured as lamellar boundaries in that of pure nickel and as elongated grains in that of pure aluminum underwent a same strain level of ECAP. Results of mechanical properties show that yield strength and microhardness increase as strain increase up to a max value in copper, and then begin to decrease slightly, while mechanical properties of the other two increase as strain increases in nickel up to a strain level of ~12, and as in aluminum, yield strength and microhardness increase as strain increase in a relative low strain level, and then reach an saturation value.
Improvement of Strength of Mg-12Gd-3Y-0.5Zr Alloys Processed by Combination of ECAP and Extrusion
Authors: Zhu Rong , Liu Jin Qiang , Wang Jing Tao , Huang Ping , Wu Yan Jun , Zhao Xiang
Published: March 2011

Equal channel angular pressing (ECAP) has been used to refine the grain size of Mg-12Gd-3Y-0.5Zr billet at about 400°C because it lacks sufficient ductility at low temperatures. However, <0001> peak intensity is oriented about 50º from the extrusion direction, which facilitates the basal slip, and decreases the yield strength. We have employed conventional extrusion at 300°C following ECAP to modify the texture in hard orientation. This two-step process makes use of two strengthening mechanisms a) grain boundary strengthening due to small grain size, and (b) texture strengthening due to grains in hard orientation. The samples processed by the two-step show the yield and ultimate strength to 283 and 308 MPa, respectively. Moreover, the activation of  slip and fine grains resulted from the ECAP helped to maintain a good ductility even after significant straining from conventional extrusion.