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Reinhart Poprawe - One of the best experts on this subject based on the ideXlab platform.

  • The Influence of the Powder Stream on High-Deposition-Rate Laser Metal Deposition with Inconel 718
    Metals, 2017
    Co-Authors: Chongliang Zhong, Andres Gasser, Reinhart Poprawe, Norbert Pirch, Johannes Henrich Schleifenbaum
    Abstract:

    For the purpose of improving the productivity of laser metal Deposition (LMD), the focus of current research is set on increasing the Deposition Rate, in order to develop High-Deposition-Rate LMD (HDR-LMD). The presented work studies the effects of the powder stream on HDR-LMD with Inconel 718. Experiments have been designed and conducted by using different powder feeding nozzles—a three-jet and a coaxial powder feeding nozzle—since the powder stream is mainly determined by the geometry of the powder feeding nozzle. After the Deposition trials, metallographic analysis of the samples has been performed. The laser intensity distribution (LID) and the powder stream intensity distribution (PID) have been characterized, based on which the processes have been simulated. Finally, for verifying and correcting the used models for the simulation, the simulated results have been compared with the experimental results. Through the conducted work, suitable boundary conditions for simulating the process with different powder streams has been determined, and the effects of the powder stream on the process have also been determined. For a LMD process with a three-jet nozzle a substantial part of the powder particles that hit the melt pool surface are rebounded; for a LMD process with a coaxial nozzle almost all the particles are caught in the melt pool. This is due to the different particle velocities achieved with the two different nozzles. Moreover, the powder stream affects the heat exchange between the heated particles and the melt pool: a surface boundary condition applies for a powder stream with lower particle velocities, in the experiment provided by a three-jet nozzle, and a volumetric boundary condition applies for a powder stream with Higher particle velocities, provided by a coaxial nozzle.

  • a comparative study of inconel 718 formed by High Deposition Rate laser metal Deposition with ga powder and prep powder
    Materials & Design, 2016
    Co-Authors: Chongliang Zhong, Andres Gasser, Reinhart Poprawe, Shang Sui, Jing Chen, Stefanie Linnenbrink
    Abstract:

    Abstract A comparative study on the metallurgical properties and material microstructures of Inconel 718 (IN718) deposited by High Deposition Rate Laser Metal Deposition (HDR-LMD) using Gas Atomization (GA) and Plasma-rotating Electrode Process (PREP) powders has been carried out. Initially, powders of same nominal particle size produced by different methods were selected and the chemical composition, porosity and morphology of which have been characterized. After that, parallel experiments have been designed and performed, and the metallurgical properties and material microstructures have been analyzed. It is found: compared to IN718 deposited with PREP powder, material formed by GA powder has Higher porosity and Higher dilution zone whereas finer dendrite structure, lower Nb element segregation and lower volume fraction of Laves phase. In order to figure out the reasons, the mechanisms of pores formation, the laser energy allocation, heat dissipation and solidification of the processes using different powders have been qualitative and quantitative analyzed. It concludes: the High porosity of GA IN718 is due to that more gas has been drawn into the process because of the characteristics of GA powder; the microstructures of GA IN718 is superior to that of PREP powder, showing finer dendrite structure, lower Nb segregation and lower Laves phase fraction, which is due to its Higher cooling Rate.

  • improvement of material performance of inconel 718 formed by High Deposition Rate laser metal Deposition
    Materials & Design, 2016
    Co-Authors: Chongliang Zhong, Andres Gasser, Jochen Kittel, Konrad Wissenbach, Reinhart Poprawe
    Abstract:

    Abstract As precipitation hardening nickel-based super-alloy, the mechanical properties of Inconel 718 (IN718) formed by High Deposition-Rate LMD (HDR-LMD) are far lower than the relevant specifications, making it unable to be used in practical industry applications. With the purpose of improving its material performance, the current study has been carried out. The microstructure characteristics of the as-deposited IN718 have been analysed, and the mechanical properties of it have been tested. Based on which, reasons that result in its poor mechanical properties have been identified. Furthermore, aiming to solve these problems the methods in order to improve material performance have been studies. It is found: the poor mechanical properties of the as-deposited IN718 could be significantly improved by HIPing (Hot Isostatic Pressing) and proper heat treatments. In addition, the mechanical properties of the heat-treated material are superior to AMS specifications for IN718 fabricated by conventional manufacturing processes. It concluded: HIP can dramatically reduce the porosity of the as-deposited material; the columnar grains can be transformed to equiaxed grains by homogenization, eliminating material anisotropy; Laves phase could be dissolved by solution treatment, transforming to needle-like δ phase; strengthening phases will be precipitated by double aging, therefore strengthening/hardening the material.

  • Microstructures and tensile properties of Inconel 718 formed by High Deposition-Rate laser metal Deposition
    Journal of Laser Applications, 2016
    Co-Authors: Chongliang Zhong, Andres Gasser, Jochen Kittel, Yalin Ding, Reinhart Poprawe
    Abstract:

    The aim of this study is to characterize microstructures and tensile properties of Inconel 718 (IN718) formed by High Deposition-Rate laser metal Deposition (LMD), and furthermore to verify that the properties of the material are equivalent to those obtained by conventional manufacturing processes, such as casting and forging, and therefore satisfy the specifications for industrial applications. Initially, the powdery additive was characterized in terms of chemical composition, morphology, and porosity. Afterward, blocks for producing tensile specimens were deposited by applying the newly developed High Deposition-Rate LMD process that has a Deposition Rate of approximately 2 kg/h. Finally, microstructures and tensile properties of directly deposited and heat-treated material were analyzed, respectively. From the results, precipitation of an irregular shaped phase, which is believed to be Laves phase, and segregation of Nb and Mo were found at interdendritic regions of the directly deposited material. The...

  • experimental study of effects of main process parameters on porosity track geometry Deposition Rate and powder efficiency for High Deposition Rate laser metal Deposition
    Journal of Laser Applications, 2015
    Co-Authors: Chongliang Zhong, Andres Gasser, Tim Biermann, Reinhart Poprawe
    Abstract:

    Laser metal Deposition (LMD) is an additive manufacturing process. Although much research regarding effects of process parameters on Deposition quality has been conducted in recent decades, the studies in this field are still lacking for High Deposition Rates (>0.3 kg/h) LMD. Most of the previous investigations were based on traditional LMD process, characterized by a low Deposition Rate (<0.3 kg/h). This paper presents a pilot study to find the answer on the effects of main process parameters on track dimensions and process characteristics in High Deposition-Rate LMD. Inconel 718 (IN718) powder was used as additive material. Chemical composition, porosity, shape, and morphology of the used powder were analyzed to ensure that the necessary specifications are met. Based on a High Deposition-Rate LMD process, which has a Deposition Rate of approximately 2 kg/h, experiments were designed and carried out on a dedicated High Deposition-Rate LMD experimental setup. Furthermore, effects of main process parameter...

Friedhelm Finger - One of the best experts on this subject based on the ideXlab platform.

  • Open circuit voltage improvement of High-Deposition-Rate microcrystalline silicon solar cells by hot wire interface layers
    Applied Physics Letters, 2005
    Co-Authors: Y. Mai, Stefan Klein, R. Carius, Helmut Stiebig, Xinhua Geng, Friedhelm Finger
    Abstract:

    Significant improvement in open circuit voltage and fill factor was achieved for microcrystalline silicon (μc‐Si:H) solar cells deposited by plasma-enhanced chemical vapor Deposition (PECVD) by the incorporation of an intrinsic μc‐Si:Hp∕i buffer layer fabricated by hot-wire (HW) CVD. The improved p∕i interface quality, likely due to the ion-free Deposition on the p layers in the HWCVD process, was concluded from a considerably enhanced blue light response in such solar cells. Using this buffer layer concept allows the authors to apply High Deposition Rate PECVD processes for the μc‐Si:Hi layer material, yielding a High efficiency of 10.3% for a single junction μc‐Si:H solar cell.

  • structure adjustment during High Deposition Rate growth of microcrystalline silicon solar cells
    Applied Physics Letters, 2004
    Co-Authors: Y. Mai, Stefan Klein, Xinhua Geng, Friedhelm Finger
    Abstract:

    Preparation of microcrystalline silicon for solar cell applications is investigated under High-pressure, High-power conditions with plasma-enhanced chemical vapor Deposition at 95MHz. It is found that the Deposition Rate depends mainly on the amount of silane in the reaction zone. Changes in the discharge power affect the Deposition Rate very little. This points to silane depletion under these process conditions. The amount of H radicals, on the other hand, increases with increasing discharge power and leads to structure changes of the material. Making use of this effect, optimum phase mixture material at the transition from Highly crystalline to amorphous growth can be deposited at considerably Higher Deposition Rates without loss in solar cell performance.

Chongliang Zhong - One of the best experts on this subject based on the ideXlab platform.

  • Study of nickel-based super-alloys Inconel 718 and Inconel 625 in High-Deposition-Rate laser metal Deposition
    Optics & Laser Technology, 2019
    Co-Authors: Chongliang Zhong, Andres Gasser, Jochen Kittel, Johannes Henrich Schleifenbaum
    Abstract:

    Abstract Nickel-based super-alloys Inconel 718 (IN718) and Inconel 625 (IN625) have comparable chemical composition and similar physical constants such as density and melting range; however, in High-Deposition-Rate laser metal Deposition (HDR-LMD), processes with IN625 are not transferable to that with IN718. In order to compare HDR-LMD process with IN718 and IN625, the current study has been conducted. Initially, parallel experiments have been performed, and the metallurgical analysis for macro- and microstructures have been carried out. Then, the strengthening effects of HDR-LMD for both alloys have been compared. Finally, in order to understand and explain the obtained results, both processes have been characterized by using a High-speed camera. According to the study, the following conclusions have been drawn: in comparison to IN718, there seems to have a stronger convection in the melt pool of IN625; this convection could be the reason for the faster solidification of IN625 since it may acceleRate the dissipation of heat; As a further consequence of the stronger convection, the degassing during the solidification can be enhanced.

  • influence of solution heat treatment on microstructure and tensile properties of inconel 718 formed by High Deposition Rate laser metal Deposition
    Journal of Alloys and Compounds, 2018
    Co-Authors: Shang Sui, Chongliang Zhong, Andres Gasser, Johannes Henrich Schleifenbaum, Weidong Huang, Jing Chen
    Abstract:

    Abstract The influence of solution heat treatment on microstructure and tensile property of Inconel 718 formed by High-Deposition-Rate laser metal Deposition has been investigated in this paper. Two different heat treatment regimes were employed: 1100 °C × 0.5 h/WQ+720 °C × 8 h/FC to 620 °C × 8 h/AC (this type of samples is called type-S) and 1100 °C × 1 h/WQ+720 °C × 8 h/FC to 620 °C × 8 h/AC (this type of samples is called type-L). The results showed that niobium segregation and Laves phases were eliminated both in type-S and type-L samples. This means that heat treatment at 1100 °C for no more than 0.5 h is enough, if initial epitaxial columnar grains are needed and niobium segregation and Laves phases are tend to be removed. Twins only existed in type-L sample, which was the main reason why the elongation of type-L was superior to that of type-S. The fracture mechanism of these two samples was microvoids coalescence ductile rupture. The separation of the granular sub-micron particles and the γ matrix was the main nucleus of the micro-voids.

  • The Influence of the Powder Stream on High-Deposition-Rate Laser Metal Deposition with Inconel 718
    Metals, 2017
    Co-Authors: Chongliang Zhong, Andres Gasser, Reinhart Poprawe, Norbert Pirch, Johannes Henrich Schleifenbaum
    Abstract:

    For the purpose of improving the productivity of laser metal Deposition (LMD), the focus of current research is set on increasing the Deposition Rate, in order to develop High-Deposition-Rate LMD (HDR-LMD). The presented work studies the effects of the powder stream on HDR-LMD with Inconel 718. Experiments have been designed and conducted by using different powder feeding nozzles—a three-jet and a coaxial powder feeding nozzle—since the powder stream is mainly determined by the geometry of the powder feeding nozzle. After the Deposition trials, metallographic analysis of the samples has been performed. The laser intensity distribution (LID) and the powder stream intensity distribution (PID) have been characterized, based on which the processes have been simulated. Finally, for verifying and correcting the used models for the simulation, the simulated results have been compared with the experimental results. Through the conducted work, suitable boundary conditions for simulating the process with different powder streams has been determined, and the effects of the powder stream on the process have also been determined. For a LMD process with a three-jet nozzle a substantial part of the powder particles that hit the melt pool surface are rebounded; for a LMD process with a coaxial nozzle almost all the particles are caught in the melt pool. This is due to the different particle velocities achieved with the two different nozzles. Moreover, the powder stream affects the heat exchange between the heated particles and the melt pool: a surface boundary condition applies for a powder stream with lower particle velocities, in the experiment provided by a three-jet nozzle, and a volumetric boundary condition applies for a powder stream with Higher particle velocities, provided by a coaxial nozzle.

  • a comparative study of inconel 718 formed by High Deposition Rate laser metal Deposition with ga powder and prep powder
    Materials & Design, 2016
    Co-Authors: Chongliang Zhong, Andres Gasser, Reinhart Poprawe, Shang Sui, Jing Chen, Stefanie Linnenbrink
    Abstract:

    Abstract A comparative study on the metallurgical properties and material microstructures of Inconel 718 (IN718) deposited by High Deposition Rate Laser Metal Deposition (HDR-LMD) using Gas Atomization (GA) and Plasma-rotating Electrode Process (PREP) powders has been carried out. Initially, powders of same nominal particle size produced by different methods were selected and the chemical composition, porosity and morphology of which have been characterized. After that, parallel experiments have been designed and performed, and the metallurgical properties and material microstructures have been analyzed. It is found: compared to IN718 deposited with PREP powder, material formed by GA powder has Higher porosity and Higher dilution zone whereas finer dendrite structure, lower Nb element segregation and lower volume fraction of Laves phase. In order to figure out the reasons, the mechanisms of pores formation, the laser energy allocation, heat dissipation and solidification of the processes using different powders have been qualitative and quantitative analyzed. It concludes: the High porosity of GA IN718 is due to that more gas has been drawn into the process because of the characteristics of GA powder; the microstructures of GA IN718 is superior to that of PREP powder, showing finer dendrite structure, lower Nb segregation and lower Laves phase fraction, which is due to its Higher cooling Rate.

  • improvement of material performance of inconel 718 formed by High Deposition Rate laser metal Deposition
    Materials & Design, 2016
    Co-Authors: Chongliang Zhong, Andres Gasser, Jochen Kittel, Konrad Wissenbach, Reinhart Poprawe
    Abstract:

    Abstract As precipitation hardening nickel-based super-alloy, the mechanical properties of Inconel 718 (IN718) formed by High Deposition-Rate LMD (HDR-LMD) are far lower than the relevant specifications, making it unable to be used in practical industry applications. With the purpose of improving its material performance, the current study has been carried out. The microstructure characteristics of the as-deposited IN718 have been analysed, and the mechanical properties of it have been tested. Based on which, reasons that result in its poor mechanical properties have been identified. Furthermore, aiming to solve these problems the methods in order to improve material performance have been studies. It is found: the poor mechanical properties of the as-deposited IN718 could be significantly improved by HIPing (Hot Isostatic Pressing) and proper heat treatments. In addition, the mechanical properties of the heat-treated material are superior to AMS specifications for IN718 fabricated by conventional manufacturing processes. It concluded: HIP can dramatically reduce the porosity of the as-deposited material; the columnar grains can be transformed to equiaxed grains by homogenization, eliminating material anisotropy; Laves phase could be dissolved by solution treatment, transforming to needle-like δ phase; strengthening phases will be precipitated by double aging, therefore strengthening/hardening the material.

Scott Morrison - One of the best experts on this subject based on the ideXlab platform.

  • Progress in High Deposition Rate amorphous and polycrystalline silicon materials using the pulsed plasma and hot wire CVD Deposition techniques
    Solar Energy Materials and Solar Cells, 1999
    Co-Authors: Arun Madan, Scott Morrison, Hajime Kuwahara
    Abstract:

    Abstract The pulsed plasma Deposition can increase the Deposition Rate of amorphous silicon (a-Si) without an increase in the particulate count in the plasma which is an important factor determining the yield of commercial products such as active matrix displays. In this paper, we report the Deposition of a-Si at Rates of up to 15 A/sec, using a modulation frequency in the range of 1–100 kHz and the impact it has on solar cell conversion efficiency. The hot wire CVD Deposition technique has attracted a considerable amount of interest because of the ability to produce a-Si at a High Deposition Rate and with low hydrogen concentration which could minimize the instability phenomena. Further, under suitable conditions, low temperature polycrystalline silicon can be produced. We present data of High Deposition Rates for a-Si (>15 A/s) and polycrystalline Si and discuss their usefulness to photovoltaic applications.

  • High Deposition Rate amorphous and polycrystalline silicon materials using the pulsed plasma and “Hot-Wire” CVD techniques
    Solar Energy Materials and Solar Cells, 1998
    Co-Authors: Arun Madan, Scott Morrison
    Abstract:

    Abstract The cost of amorphous silicon solar panels are dictated by the Deposition Rate, the utilization Rate of the silane gas and stability issues. In this context, we present data of amorphous silicon materials and solar cells using pulsed plasma PECVD (plasma enhanced chemical vapor Deposition) technique with the i-layer fabricated with High Deposition Rates. “Hot-Wire” CVD Deposition technique has attracted a considerable amount of interest because of the ability to produce amorphous silicon at High Deposition Rates and with low hydrogen concentration of H which could minimize the stability phenomena. Further, under suitable conditions, low-temperature polycrystalline silicon can be produced. We present data of High Deposition Rates of polycrystalline Si (∼10 A/s) and discuss its potential usefulness in a hybrid tandem (combination of amorphous and polycrystalline) junctions.

Y. Mai - One of the best experts on this subject based on the ideXlab platform.

  • Open circuit voltage improvement of High-Deposition-Rate microcrystalline silicon solar cells by hot wire interface layers
    Applied Physics Letters, 2005
    Co-Authors: Y. Mai, Stefan Klein, R. Carius, Helmut Stiebig, Xinhua Geng, Friedhelm Finger
    Abstract:

    Significant improvement in open circuit voltage and fill factor was achieved for microcrystalline silicon (μc‐Si:H) solar cells deposited by plasma-enhanced chemical vapor Deposition (PECVD) by the incorporation of an intrinsic μc‐Si:Hp∕i buffer layer fabricated by hot-wire (HW) CVD. The improved p∕i interface quality, likely due to the ion-free Deposition on the p layers in the HWCVD process, was concluded from a considerably enhanced blue light response in such solar cells. Using this buffer layer concept allows the authors to apply High Deposition Rate PECVD processes for the μc‐Si:Hi layer material, yielding a High efficiency of 10.3% for a single junction μc‐Si:H solar cell.

  • structure adjustment during High Deposition Rate growth of microcrystalline silicon solar cells
    Applied Physics Letters, 2004
    Co-Authors: Y. Mai, Stefan Klein, Xinhua Geng, Friedhelm Finger
    Abstract:

    Preparation of microcrystalline silicon for solar cell applications is investigated under High-pressure, High-power conditions with plasma-enhanced chemical vapor Deposition at 95MHz. It is found that the Deposition Rate depends mainly on the amount of silane in the reaction zone. Changes in the discharge power affect the Deposition Rate very little. This points to silane depletion under these process conditions. The amount of H radicals, on the other hand, increases with increasing discharge power and leads to structure changes of the material. Making use of this effect, optimum phase mixture material at the transition from Highly crystalline to amorphous growth can be deposited at considerably Higher Deposition Rates without loss in solar cell performance.