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Showing papers in "Materials Science Forum in 2015"


Journal ArticleDOI
TL;DR: In this article, a block voltage of 27 kV, 20 A 4H-SiC n-IGBTs was achieved by utilizing thick (210 μm and 230 μm), lightly doped N-drift layers with an appropriate edge termination.
Abstract: In this work, we report our recently developed 27 kV, 20 A 4H-SiC n-IGBTs. Blocking voltages exceeding 24 kV were achieved by utilizing thick (210 μm and 230 μm), lightly doped N-drift layers with an appropriate edge termination. Prior to the device fabrication, an ambipolar carrier lifetime of greater than 10 μs was measured on both drift regions by the microwave photoconductivity decay (μPCD) technique. The SiC n-IGBTs exhibit an on-state voltage of 11.8 V at a forward current of 20 A and a gate bias of 20 V at 25 °C. The devices have a chip size of 0.81 cm2 and an active conducting area of 0.28 cm2. Double-pulse switching measurements carried out at up to 16 kV and 20 A demonstrate the robust operation of the device under hard-switched conditions; coupled thermal analysis indicates that the devices can operate at a forward current of up to 10 A in a hard-switched environment at a frequency of more than 3 kHz and a bus voltage of 14 kV.

122 citations


Journal ArticleDOI
TL;DR: In this article, X-ray diffraction technique was used for investigating the residual stress induced into SLM Ti6Al4V alloy samples and principal stresses were estimated for the cut rectangular specimen.
Abstract: Selective Laser Melting (SLM) presents a modern manufacturing process with an innovative technology which allows the production of full-density objects or fine-structured parts with complex geometry and inner structures. Stability and certification of the properties of SLM parts are important tasks for all producers and end-users. One of the drawbacks of this technology is high residual stress in as-made SLM objects. In this study X-ray diffraction technique was used for investigating the residual stress induced into SLM Ti6Al4V alloy samples. Principal stresses were estimated for the cut rectangular specimen. Two types of the cantilevers were produced and numerical simulation of the stress was performed. The bending of cut cantilevers was measured before and after heat treatment. Next series of the samples had rectangular shapes and different thicknesses from 1 to 46 layers. All as-manufactured specimens attached to the substrate showed the presence of tensile residual stresses near the top surface. Residual stress along the laser scanning direction had magnitudes twice that of the stress in the perpendicular direction. Conclusions regarding directions and values of stresses in SLM objects from Ti6Al4V powder are given.

55 citations


Journal ArticleDOI
TL;DR: In this paper, the authors summarized the recent overall views of delafossite nanoparticles in diverse applications such as energy, catalysis, photocatalysis, nanomedicine, sensors, electrochemical devices and environmental concerns.
Abstract: Recently, numerous delafossite oxides in nanoscale have been reported for diverse applications. The present review summarized the recent overall views of delafossite nanoparticles in diverse applications such as energy, catalysis, photocatalysis, nanomedicine, sensors, electrochemical devices and environmental concerns. Delafossite nanoparticles possess unique features such as different and wide chemical composition, large surface area, small energy gap, ability for further functionalization, possess dual-active sites with different oxidation states (A+ and M3+), and eager for doping with various species with feasibility to undergo structure modification. Thus, they provided promising application such as solar cell, photocatalysis, hydrogen production, bioactive materials, separation purposes and others. Pros, cons, current and future status were also reviewed.

53 citations


Journal ArticleDOI
TL;DR: In this paper, a method of temperature measurement of the molten pool surface on metallic plates and during melting of metal powder layer, that were exposed to laser radiation, using an infrared camera (IR), in the present case FLIR Phoenix RDAS TM, was proposed.
Abstract: The objective of this study is to restore the true temperature in during the process of Selective Laser Melting (SLM) of metal powder (in the present case INOX 316L), that is the actual problem in laser assisted additive technologies. To meet this objective, at the first stage, the temperature was measured on the surface of metal substrate INOX 304L without a powder layer. Based on the results of studies the method of temperature measurementof the molten pool surface on metallic plates and during melting of metal powder layer, that were exposed to laser radiation, using an infrared camera (IR), in the present case FLIR Phoenix RDAS TM, was proposed. To restore the true temperature based on the brightness temperature values measured by IR camera, the results of temperature measurements were compared with the width of the molten track on the surface of the plate in the absence of powder. In case of SLM, the results of IR camera measurements were compared with the width of a welded track (bead). The true temperature profiles and temperature gradients values were determined along the axis of the laser beam for melting of plates without powder. In the case of powder melting, the developed method allows to determine the influence of several key SLM parameters on the molten pool shape.

43 citations


Journal ArticleDOI
TL;DR: In this paper, the morphology of magnetite nanoparticles has been evaluated by Transmission Electron Microscopy (TEM) and X-ray Diffractometer (XRD) and Vibrating Sample Magnetometer (VSM).
Abstract: Natural sand-based magnetite nanoparticles have been succesfully synthesized by coprecipitation method at room temperature. Magnetite nanoparticles were investigated by X-ray Diffractometer (XRD) and Vibrating Sample Magnetometer (VSM). The morphology of magnetite nanoparticles has been evaluated by Transmission Electron Microscopy (TEM). Qualitative analysis of XRD data reveals that the structure of magnetite nanoparticles have the same phase of ICSD No. 82237. On the other hand, quantitative analysis shows that the crystallite size of magnetite nanoparticles have ranges between 8.89 nm to 12.49 nm. The average diameter of magnetite nanoparticles increase with the increase the stirring rate of reaction when the stirring rate is lower than 1000 rpm, while the crystallite size of magnetite particles decrease with the increase the stirring rate when the stirring rate is higher than 1000 rpm. The stirring rate of reaction influence the the magnetic properties of magnetite nanoparticles. The results of the best magnetic respon are revealed for the stirring rate of 1000 rpm with the larger the crystallite size of magnetite nanoparticles due to its stronger saturation magnetization.

34 citations


Journal ArticleDOI
TL;DR: In this paper, the nano-structural behaviors such as phase purity and crystal structure of magnetite particles in ferrofluid were studied by means of X-ray diffractometry (XRD).
Abstract: Ferrofluid (magnetite/Fe3O4 magnetic fluid) is colloidal suspension containing Fe3O4 nanoparticles dispersed in a liquid carrier. In this work, Fe3O4 particles in the fluid have been prepared by a simple co-precipitation route. The nano-structural behaviors such as phase purity and crystal structure of magnetite particles in ferrofluid were studied by means of X-ray diffractometry (XRD). Meanwhile, the form and structure factors were investigated by small-angle neutron scattering (SANS) spectrometer. The XRD pattern confirmed a single phase of spinel cubic Fe3O4 structure. Further XRD data analysis revealed that the magnetite has a lattice parameter of 8.38 A. The SANS data was fitted by applying a lognormal spherical calculation as a form factor and a mass fractal model as a structure factor. It showed that the magnetite ferrofluid has primary particles of 7.6 nm in diameter with fractal dimension of 1.2, which can be associated with chain-like structure. The chain-like structured Fe3O4 ferrofluid based on local natural iron sand in this work opens new opportunities to be applied for novel prospective applications.

32 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used FTIR, Uv-Vis and XRD spectroscopy to search reduced graphene oxide (RGO) phase by identifying the molecular bonding, energy band gap and phase of old coconut shell.
Abstract: The purpose of this work is to search reduced graphene oxide (RGO) phase by identifying the molecular bonding, energy band gap and phase of old coconut shell. The characterization was performed by using FTIR, Uv-Vis and XRD spectroscopy. The heating temperature used in this work was 400°C and 600°C. Furthermore, the type of heating atmosphere used in this research covers nitrogen, ambient air with and without rinsing step. The XRD analysis shows that the RGO phase is formed by turbostatic structure which is a pile of random arrangement of parallel layers that make up the graphite structure with cliftonite phase at temperature 400°C and 600°C. In the inert nitrogen gas treatment, there are two impurity phases such as potassium chlorate (KClO4) and sulfur (S11). The molecular bondings of C=C, C-C, C-O, C=O, C-H and O-H appeared on the FTIR spectra of the samples were indentified. Analysis by using linear regression and absorbance edge methods was conducted to result in energy gap in the range from 0.14 to 0.67 eV, indicating that the produced samples are semiconducting materials.

31 citations


Journal ArticleDOI
TL;DR: In this article, a stereolithography-based system was developed, which was specifically designed for the processing of highly filled photopolymers, and the powder-filled suspension enables the 3D-fabrication of a so called ceramic green part.
Abstract: Within the large variety of different additive manufacturing technologies stereolithography excels in high precision and surface quality. Using the Digital Light Processing (DLP) Technology a stereolithography-based system was developed, which is specifically designed for the processing of highly filled photopolymers.The powder-filled suspension enables the 3D-fabrication of a so called ceramic green part. In order to get a dense ceramic structure, subsequent thermal processing steps after the 3D-printing process are necessary. First, the polymer-ceramic composites heated up to 400°C. During this processing step, called debinding, the organic components are burned out. The resulting part, consisting of powder particles stabilized by physical interactions, is further heated to sinter the particles together, and the final, fully dense ceramic part is obtained.The debinding step is the most critical process. The used components have different evaporation or decomposition temperatures and behaviors. Thereby a reduction in weight and also in dimension occurs, which depends on the portion and composition of the organic components and especially on the temperature cycle. Furthermore, the physical characteristics of the ceramic powder, such as the particle size and the size distribution influence the debinding behavior. To measure the changes in weight and dimension a thermo-gravimetric (TGA) and a thermo-mechanical analysis (TMA) can be used. To avoid too high internal gas pressures inside the green parts a preferably constant gas evolution rate is seeked. Also the ‘surface-to-volume ratio’ affects the debinding characteristics. Therefore, optimized debinding cycles for specific geometries allow the crack-free debinding of parts with a wall thickness up to 20 mm.

26 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compared the impact of selected pre-treatment, blasting medium and blasting conditions on surface finish quality of FDM prototypes and found that the results showed that the effect of selecting the pretreatment, medium and blasting conditions had a significant impact on the quality of the FDM surface finish.
Abstract: Additive manufacturing technologies decrease production time and costs in engineering industry but also in other industries. Parts produced with Fused Deposition Modeling (FDM) have typical low surface finish quality. This paper is aimed on research of surface finishing technologies applicable to improve the quality of FDM prototypes surface finish. Pretreated samples were blasted with sodium bicarbonate and glass beads. The values of Ra and Rz were measured on the samples and compared the impact of selected pre-treatment, blasting medium and blasting conditions on surface finish quality of FDM prototypes.

24 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe a non-isolated bidirectional full SiC 800V 200kW DCDC-converter power stage for electric and hybrid vehicles that reaches a power density of more than 100 kW/dm3 at a switching frequency of 200 kHz.
Abstract: This Paper describes a non-isolated bidirectional full SiC 800V 200kW DCDC-converter power stage for electric and hybrid vehicles that reaches a power density of more than 100 kW/dm3 at a switching frequency of 200 kHz. The high power density is achieved by the use of SiC-MOSFETs sintered on custom made Si3N4 DCB-substrates controlled by custom made extremely flat drivers and a resulting very low inductive DC-link connection. All passive components like inductors and capacitor boards are custom made in order to keep all parasitic effects as low as possible. The power is subdivided on six interleaved phases to reduce the required capacitor ripple current capability.

24 citations


Journal ArticleDOI
TL;DR: In this paper, hot isostatic pressing (HIP) is used to produce composite material tungsten fiber-reinforced Tungsten (Wf/W) by extrinsic toughening.
Abstract: The composite material tungsten fiber-reinforced tungsten (Wf/W) addresses the brittleness of tungsten by extrinsic toughening through introduction of energy dissipation mechanisms. These mechanisms allow the release of stress peaks and thus improve the materials resistance against crack growth. Wf/W samples produced via chemical vapor infiltration (CVI) indeed show higher toughness in mechanical tests than pure tungsten. By utilizing powder metallurgy (PM) one could benefit from available industrialized approaches for composite production and alloying routes. In this contribution the PM method of hot isostatic pressing (HIP) is used to produce Wf/W samples. A variety of measurements were conducted to verify the operation of the expected toughening mechanisms in HIP Wf/W composites. The interface debonding behavior was investigated in push-out tests. In addition, the mechanical properties of the matrix were investigated, in order to deepen the understanding of the complex interaction between the sample preparation and the resulting mechanical properties of the composite material. First HIP Wf/W single-fiber samples feature a compact matrix with densities of more than 99% of the theoretical density of tungsten. Scanning electron microscopy (SEM) analysis further demonstrates an intact interface with indentations of powder particles at the interface-matrix boundary. First push-out tests indicate that the interface was damaged by HIPing.

Journal ArticleDOI
TL;DR: In this article, small prototype pipes are manufactured based on optimized pipe design parameters for collapse under external pressure and burst under internal pressure using ANSYS 13 FEA analysis software, and experiments are conducted to verify the axial and hoop compressive strengths of the pipes with analytical results.
Abstract: The major challenge for producing and manufacturing risers for oil and gas production is to make them light weight so as to reduce the operational cost and improve the overall system requirements to make them an attractive option for marine and offshore industries. In the current research, the composite and metal-composite pipes (1) GFRP only (2) Al-GFRP and (3) PE-GFRP have been manufactured using filament winding machine operated using CADFIL and CADWIND CNC packages. The use of liners (Al and PE) has ensured the fluid tightness and collapse resistance of the pipe system. Small prototype pipes are manufactured based on optimized pipe design parameters for collapse under external pressure and burst under internal pressure using ANSYS 13 FEA analysis software. Experiments are conducted to verify the axial and hoop compressive strengths of the pipes with analytical results. The details of pipe manufacturing process using filament winding machine, simulation procedure to optimize the pipe parameters and validation of the simulation results with experimental results are the focal points of the current work.

Journal ArticleDOI
TL;DR: In this paper, a flip-type n-channel implantation and epitaxial (IE)-IGBTs were developed, and the static and dynamic performance of IE-IGBT was investigated.
Abstract: Ultrahigh-voltage SiC flip-type n-channel implantation and epitaxial (IE)-IGBTs were developed, and the static and dynamic performance was investigated. A large device (8 mm × 8mm) with a blocking voltage greater than 16 kV was achieved, and an on-state current of 20 A was obtained at the low on-state voltage (Von) of 4.8 V. RonAdiff was 23 mΩ·cm2 at Von = 4.8 V. In order to evaluate the switching characteristics of the IE-IGBT, ultrahigh-voltage power modules were assembled. A chopper circuit configuration was used to evaluate the switching characteristics of the IE-IGBT. Smooth turn-off waveforms were successfully obtained at VCE = 6.5 kV and ICE = 60 A in the temperature range from room temperature to 250°C.

Journal ArticleDOI
TL;DR: In this article, a planar MOSFET with voltage ratings from 900 V to 15 kV is presented, where the specific on-resistance of the MOS-FETs is approaching the theoretical limit.
Abstract: A family of planar MOSFETs with voltage ratings from 900 V to 15 kV are demonstrated. This family of planar MOSFETs represents Cree’s next generation MOSFET design and process, in which we continue to refine and evolve device design and processing to further shrink die sizes and enhance device performance. At voltage ratings of 3.3 kV and above, the specific on-resistance of the MOSFETs is approaching the theoretical limit. MOSFET switching performance in a clamped inductive switching circuit for the full range of voltage ratings is also demonstrated. Finally, improved threshold voltage and body diode stability under long-term stresses are presented.

Journal ArticleDOI
TL;DR: ExoMet Project funded by the EC/FP7 (GA NMP3-LA-2012-280421); Doshormat Project as mentioned in this paper (GA 606090); and UltraMelt project funded by EPSRC (contract EP/K005804/1)
Abstract: ExoMet Project funded by the EC/FP7 (GA NMP3-LA-2012-280421); Doshormat Project funded by the EC/FP7 (GA 606090); and the UltraMelt project funded by EPSRC (contract EP/K005804/1)

Journal ArticleDOI
TL;DR: In this paper, the authors show that the Ba-modified MOSFETs show a slight decrease in mobility with heating to 150 °C, as expected when mobility is not interface-trap-limited, but phonon-scattering-limited.
Abstract: Alkali (Rb, Cs) and alkaline earth elements (Sr, Ba) provide SiO2/SiC interface conditions suitable for obtaining high metal-oxide-semiconductor field-effect-transistor (MOSFET) channel mobility on the 4H-SiC Si-face (0001), without the standard nitric oxide (NO) anneal. The alkali elements Rb and Cs result in field-effect mobility (μFE) values >25 cm2/V.s, and the alkaline earth elements Sr and Ba resulted in higher μFE values of 40 and 85 cm2/V.s, respectively. The Ba-modified MOSFETs show a slight decrease in mobility with heating to 150 °C, as expected when mobility is not interface-trap-limited, but phonon-scattering-limited. The interface state density is lower than that obtained with nitric oxide (NO) passivation. Devices with a Ba interface layer maintain stable mobility and threshold voltage under ±2 MV/cm gate bias stress at 175 °C, indicating no mobile ions.

Journal ArticleDOI
TL;DR: Two versions of Schmitt trigger, an emitter-coupled and an operational amplifier (opamp)-based, are implemented in 4H-SiC bipolar technology and tested up to 500 °C as mentioned in this paper.
Abstract: Two versions of Schmitt trigger, an emitter-coupled and an operational amplifier (opamp)-based, are implemented in 4H-SiC bipolar technology and tested up to 500 °C. The former benefits the simplic ...

Journal ArticleDOI
TL;DR: In this article, a gel of ZnO:Ag precursor has been synthesized by sol-gel route from aqueous/alcoholic solution of zinc acetate dehydrate and silver nitrate mixture at room temperature.
Abstract: ZnO doped with 2~6 mol% Silver (Ag) photocatalyst thin films has been deposited on glass substrate by thermal spray coating with temperature deposition of 250°C. A gel of ZnO:Ag precursor has been synthesized by sol-gel route from aqueous/alcoholic solution of zinc acetate dehydrate and silver nitrate mixture at room temperature. The morphology of ZnO:Ag films were investigated scanning electron microscopy (SEM). 3D SEM images of ZnO:Ag thin films show the rough morphology with roughness mean square (rms) of 150 to 195 nm. The grain size of ZnO:Ag films were found in the range 76,5 to 304,8 nm. The photoactivity examination of ZnO:Ag photocatalyst films show the E. Coli bacteria degraded up to 99.99% under sunlight irradiation for 4 hours.

Journal ArticleDOI
TL;DR: In this paper, the authors show that the heteroepitaxial growth of 3C-SiC on Si (001) and Si (111) substrates deeply patterned at a micron scale by low-pressure chemical vapor deposition is shown to lead to space-filling isolated structures resulting from a mechanism of self-limitation of lateral expansion.
Abstract: The heteroepitaxial growth of 3C-SiC on Si (001) and Si (111) substrates deeply patterned at a micron scale by low-pressure chemical vapor deposition is shown to lead to space-filling isolated structures resulting from a mechanism of self-limitation of lateral expansion. Stacking fault densities and wafer bowing may be drastically reduced for optimized pattern geometries.

Journal ArticleDOI
TL;DR: In this article, a planetary ball mill was used to combine Micron-sized Co powder with WC nanopowder to obtain uniform composite powder and single remelted beads and monolayers were obtained from the composite powder on the substrates of sintered WC-Co.
Abstract: Selective laser melting is a layer-by-layer technique to form a solid part from powder. The thermal cycle of this process can be as short as one millisecond and less. This is why it is favorable to obtain nanostructured materials with advanced properties. Metal matrix composite WC-Co is studied. Micron-sized Co powder was mixed with WC nanopowder in a planetary ball mill to prepare uniform composite powder. Single remelted beads and monolayers were obtained from the composite powder on the substrates of sintered WC-Co. No cracks and good adhesion to the substrate are observed. The high cooling rate up to 106 K/s explains the fine microstructures. Increasing the scanning velocity is favourable because of refining the microstructure and decreasing the balling-effect. The attained values of surface roughness are as low as 1-2 μm.

Journal ArticleDOI
TL;DR: In this article, the authors conducted monotonic compression testing on AZ31B-F magnesium alloy in both the as-received and forged conditions and showed that in the forged condition, there is potential for significant increases in both ultimate tensile strength and strain to failure.
Abstract: Monotonic compression testing was conducted on AZ31B-F magnesium alloy in both the as-received and forged conditions. Sigmoidal stress strain behaviour was the key feature in the majority of material conditions and directions corresponding to plastic behaviour where twinning de-twinning is the dominant deformation mechanism. More conventional monotonic hardening (slip deformation mechanism) was exhibited in certain material directions which initially were orthogonal to the extrusion direction in the as-received condition, but once forged are coincident with the direction of forging once forged. It was shown that in the forged condition, there is potential for significant increases in both ultimate tensile strength as well as strain to failure.

Journal ArticleDOI
TL;DR: In this article, the potential of AlMMCs as a replacement for most steels and aluminium alloys in the manufacture of automotive parts and components is discussed as well as their current status and future trends of utilisation in automotive light-weighting.
Abstract: The automotive manufacturing industry, worldwide, has been engaged in a race to produce lightweight vehicles. Consequently, the industry continues to deploy significant resources in developing and utilising advanced lightweight materials and cutting-edge technologies in the manufacture of new vehicle models that are energy efficient, more reliable, safer, more user-friendly and less polluting; without compromising the other important vehicle attributes such as, size, cargo space and payload, structural integrity, power and acceleration. Mass reduction is one consistent and cost-effective strategy that can be combined with other efficiency improvement strategies and technologies to meet the requirements of fuel economy and emission reduction. The materials used in automotive light-weighting must fulfil several criteria imposed by regulation and legislation with the environment in addition to satisfying customer requirements. The choice for light, high strength automotive materials is between advanced high-strength steel (AHSS) on one hand, and composites of aluminium (aluminium metal matrix composites (AlMMCs)), magnesium and polymers, on the other. In this paper, the potential of AlMMCs as a replacement for most steels and aluminium alloys in the manufacture of automotive parts and components is discussed as well as their current status and future trends of utilisation in automotive light-weighting.

Journal ArticleDOI
TL;DR: In this article, integrated digital circuits, fabricated in a bipolar SiC technology, have been successfully tested up to 600 °C, with stable noise margins of about 1 or 1.5 V depending on the gate design and increasing delay power consumption in the range 100 - 200 nJ.
Abstract: Integrated digital circuits, fabricated in a bipolar SiC technology, have been successfully tested up to 600 °C. Operated with-15 V supply voltage from 27 up to 600 °C OR-NOR gates exhibit stable noise margins of about 1 or 1.5 V depending on the gate design, and increasing delay-power consumption product in the range 100 - 200 nJ. In the same temperature range an oscillation frequency of about 1 MHz is also reported for an 11-stage ring oscillator.

Journal ArticleDOI
TL;DR: Infineon's 5th Generation of 1200V SiC diodes uses a new compact chip design, realized by an optimized hexagonal merged-pn cell structure in the active area, which allows a higher n-doping in the epi layer due to improved E-field shielding resulting in smaller differential resistance per chip area.
Abstract: Infineon’s 5th Generation of 1200V SiC diodes uses a new compact chip design, realized by an optimized hexagonal merged-pn cell structure in the active area. This allows a higher n-doping in the epi layer due to improved E-field shielding resulting in a smaller differential resistance per chip area. Thanks to the merged-pn cell structure, depending on the diode ampere rating, a surge current capability now rated up to 14 times the nominal current ensures robust diode operation during surge current events in the application. The previous generations of 1200V SiC diodes could not make full use of the high breakdown field strength of the SiC material due to the instable avalanche which occurs at the edge termination only, and therefore, requiring a significant safety margin between rated voltage and breakdown voltage. Now the 5th Generation is designed in a way that each cell contributes to the avalanche, enabling a much more avalanche rugged device.

Journal ArticleDOI
TL;DR: In this article, an effective way to suppress the forest dislocations and APBs which nucleate during 3C-SiC growth is proposed, which is regarded as an electrically active defect.
Abstract: Eelectrically active defects in 3C–SiC are investigated by considering the structures and interactions of planar defects. An anti-phase boundary (APB) largely degrades the blocking property of semiconductor devices due to its semimetallic nature. Although APBs can be eliminated by orienting the specific polar face of 3C-SiC along a particular direction, stacking faults (SFs) cannot be eliminated due to Shockley-type partial dislocation glide. SFs with Shockley-type partial dislocations form a trapezoidal plate which expands the Si-terminated surface with increasing 3C-SiC thickness. Although the density of SFs can be reduced by counter termination, specific cross-junctions between a pair of counter SFs forms a forest dislocation, and this is regarded as an electrically active defect. This paper proposes an effective way to suppress the forest dislocations and APBs which nucleate during 3C-SiC growth.

Journal ArticleDOI
TL;DR: In this article, the growth of 3C-SiC using sublimation growth in the temperature range from 1800°C to 1950°C was investigated using numerical modeling of the temperature field and gas phase composition by applying quasi-equilibrium thermodynamic conditions.
Abstract: We have investigated the growth of 3C-SiC using sublimation growth in the temperature range from 1800°C to 1950°C. The supersaturation was determined using numerical modeling of the temperature field and gas phase composition by applying quasi-equilibrium thermodynamic conditions. Analysis of the 3C-SiC yield was carried out by optical microscopy, optical absorption, Raman spectroscopy and x-ray analysis. Quantitative data on supersaturation are compared with most stable 3C-SiC nucleation and growth condition. Finally the application to large area growth in a physical vapor transport growth reactor is briefly addressed.

Journal ArticleDOI
TL;DR: In this paper, the reduction of process-related thermal residual stress in fiber metal laminates and its impact on the mechanical properties were investigated, and different modifications during fabrication of co-cure bonded steel/carbon epoxy composite hybrid structures were investigated.
Abstract: This paper focuses on the reduction of process-related thermal residual stress in fiber metal laminates and its impact on the mechanical properties. Different modifications during fabrication of co-cure bonded steel/carbon epoxy composite hybrid structures were investigated. Specific examinations are conducted on UD-CFRP-Steel specimens, modifying temperature, pressure or using a thermal expansion clamp during manufacturing. The impact of these parameters is then measured on the deflection of asymmetrical specimens or due yield-strength measurements of symmetrical specimens. The tensile strength is recorded to investigate the effect of thermal residual stress on the mechanical properties. Impact tests are performed to determine the influence on resulting damage areas at specific impact energies. The experiments revealed that the investigated modifications during processing of UD-CFRP-Steel specimens can significantly lower the thermal residual stress and thereby improve the tensile strength.

Journal ArticleDOI
TL;DR: In this paper, the influence of withdrawal rate on the microstructure of directionally solidified Mg-x%Zn (x=2, 4, 6) alloys was investigated.
Abstract: The influence of withdrawal rate on the microstructure of directionally solidified Mg-x%Zn (x=2, 4, 6) alloys was investigated in this paper. It was found that with the withdrawal rates increased from 20 μm/s to 60 μm/s, the morphology of the solid-liquid interface changed from planer to cellular dendrite. When the growth rate was further increased to 120 μm/s, the solidification microstructure appeared to be the typical dendrite structure with the developed secondary dendrite arms. Meanwhile, the dendrite arm spacing decreased with the increase of growth rate. Under the same solidification conditions, the microstructure went through cell branch transformation with the increase of Zn content within a lower withdrawal rate range; while the Zn content did not affect the morphology at a higher withdrawal rate. As well, the microstructure was refined gradually with the increase of Zn content. The effects of withdrawal rate and alloying content on morphology were analyzed by constitutional supercooling and the MS theory.

Journal ArticleDOI
TL;DR: In this article, a characterization of metal inserts in fiber-reinforced-plastic (FRP) parts is presented, with a specially adapted RTM mold with exchangeable cartridges for different insert geometries.
Abstract: The use of fiber-reinforced-plastics (FRP) contributes to an efficient implementation of lightweight design due to their outstanding specific mechanical properties. The RTM process offers great design freedom and allows the integration of functional elements during manufacturing. Embedded metal elements, so-called inserts, can be used to deal with the load transfer to structural parts. These elements have distinctive characteristics in comparison to other joining technologies. For example, detachable connections can be established with the help of inserts. Due to the fiber continuity not being interrupted and, subsequently, the FRP parts not having to be drilled, there is no local bearing stress. This paper aims at the characterization of metal inserts in FRP parts. The parts are manufactured using the RTM process with a specially adapted RTM mold with exchangeable cartridges for different insert geometries. The inserts are made of metal sheets with welded bushings and are embedded during preforming. The cured FRP specimens are tested under different load conditions to evaluate their suitability for various fields of application. Furthermore, the diameter and thickness of the metal sheet of the insert as well as the thickness of the FRP are varied to identify their influence on the failure behavior and load capacity under tensile loads.

Journal ArticleDOI
TL;DR: In this article, a simulation of molecular dynamics for the deposition of Titanium (Ti) and Nickel (Ni) particles on Ti substrate during cold gas dynamic spray (CGDS) process is presented.
Abstract: This paper presents simulation of molecular dynamics for the deposition of Titanium (Ti) and Nickel (Ni) particles on Ti substrate during Cold Gas Dynamic Spray (CGDS) process. The influencing factors of the deposition process, such as particle incident velocity, particle size and particle temperature are taken into consideration. Ti and Ni were selected because of their potential applications in the aerospace, marine and bio-medical industries. CGDS is preferred because it is a state of the art technique by which coatings are created without significant heating of the sprayed powder. In CGDS, particles are accelerated to supersonic velocities using a high speed gas stream. However, there are inherent difficulties in relating particle deposition characteristics with influencing factors of the deposition process. Moreover, there is limited literature on molecular dynamics simulation of CGDS process. For this reason, this paper develops a simulation process for Ti and Ni particles under influence of many factors using molecular dynamics. In this process, particles are allowed to interact for a short time, giving a view of their motion. The trajectories of these particles are determined by numerically solving the Newton's equations of motion for a system of interacting particles, in which the forces between the particles are defined. The results of the simulation process show that higher incident velocities and larger particle sizes result in stronger interface between the particle and the substrate. Further, higher temperatures of the substrate and particles improve the bond strength.