Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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Now showing 1 - 6 of 6
  • Publication
    In situ microstructure analysis of Inconel 625 during laser powder bed fusion
    ( 2022)
    Schmeiser, Felix
    ;
    Krohmer, Erwin
    ;
    Wagner, Christian
    ;
    Schell, Norbert
    ;
    Uhlmann, Eckart
    ;
    Reimers, Walter
    Laser powder bed fusion is an additive manufacturing process that employs highly focused laser radiation for selective melting of a metal powder bed. This process entails a complex heat flow and thermal management that results in characteristic, often highly textured microstructures, which lead to mechanical anisotropy. In this study, high-energy X-ray diffraction experiments were carried out to illuminate the formation and evolution of microstructural features during LPBF. The nickel-base alloy Inconel 625 was used for in situ experiments using a custom LPBF system designed for these investigations. The diffraction patterns yielded results regarding texture, lattice defects, recrystallization, and chemical segregation. A combination of high laser power and scanning speed results in a strong preferred crystallographic orientation, while low laser power and scanning speed showed no clear texture. The observation of a constant gauge volume revealed solid-state texture changes without remelting. They were related to in situ recrystallization processes caused by the repeated laser scanning. After recrystallization, the formation and growth of segregations were deduced from an increasing diffraction peak asymmetry and confirmed by ex situ scanning transmission electron microscopy.
  • Publication
    Ex Situ Residual Stress Analysis of Chemical Vapor Deposited Diamond Coated Cutting Tools by Synchrotron X-Ray Diffraction in Transmission Geometry
    ( 2021)
    Hinzmann, Daniel
    ;
    Böttcher, Katrin
    ;
    Reimers, Walter
    ;
    Uhlmann, Eckart
    When machining difficult-to-cut, nonferrous materials, chemical vapor deposited (CVD) diamond-coated cutting tools are applied. The tools' favorable mechanical property profile is based on the hardness of the coating as well as the adaptability of the substrate. Nevertheless, the reproducibility of machining results and process stability are limited by insufficient coating adhesion. The resulting cutting tool failure is based on coating delamination initiated by crack development. By assessing residual stress as an influence of coating adhesion, an analysis of CVD diamond-coated tools is performed using synchrotron X-ray diffraction in transmission geometry. Investigation of a nanocrystalline and multilayer morphology on cobalt-based tungsten carbide (WC-Co) and a silicon nitride-based ceramic (Si3N4) provides the distribution of the principal in-plane residual stress tensor component s22 depending on the coating morphology and substrate material. Contrary to microcrystalline CVD diamond, nanocrystalline layers decrease the compressive residual stress. In addition, the CVD diamond coating deposited on the Si3N4 substrate material tends to induce an overall initial tensile residual stress that leads to increased tool performance compared to WC-Co-based coated tools. Variation of the coating morphology as well as the substrate material offers the possibility to extend the current model for residual stress-dependent tool failure.
  • Publication
    Internal Stress Evolution and Subsurface Phase Transformation in Titanium Parts Manufactured by Laser Powder Bed Fusion - An In Situ X-Ray Diffraction Study
    ( 2021)
    Schmeiser, Felix
    ;
    Krohmer, Erwin
    ;
    Schell, Norbert
    ;
    Uhlmann, Eckart
    ;
    Reimers, Walter
    Laser powder bed fusion (LPBF) is a metal additive manufacturing technology, which enables the manufacturing of complex geometries for various metals and alloys. Herein, parts made from commercially pure titanium are studied using in situ synchrotron radiation diffraction experiments. Both the phase transformation and the internal stress buildup are evaluated depending on the processing parameters. For this purpose, evaluation approaches for both temperature and internal stresses from in situ diffraction patterns are presented. Four different parameter sets with varying energy inputs and laser scanning strategies are investigated. A combination of a low laser power and scanning speed leads to a more homogeneous stress distribution in the observed gauge volumes. The results show that the phase transformation is triggered during the primary melting and solidification of the powder and subsurface layers. Furthermore, the stress buildup as a function of the part height during the manufacturing process is clarified. A stress maximum is formed below the part surface, extending into deeper layers with increasing laser power. A temperature evaluation approach for absolute internal stresses shows that directional stresses decrease sharply during laser impact and reach their previous magnitude again during cooling.
  • Publication
    Wear evaluation of CVD diamond coated high-performance drilling tools for machining of carbon fiber reinforced plastics (CFRP)
    ( 2020)
    Uhlmann, Eckart
    ;
    Reimers, Walter
    ;
    Hinzmann, Daniel
    ;
    Christiansen, Gerret
    ;
    Böttcher, Katrin
    The application of carbon fiber reinforced plastics (CFRP) as lightweight construction material in aerospace industry is based on the favorable weight-to-strength ratio. But the inherent material properties pose great challenges for the tool-as well as the manufacturing industry. In terms of economic industrial production processes, the quality of machined workpieces exhibits poor reproducibility combined with high tool wear. For this purpose, high-performance drilling tools with different CVD diamond coatings and carbide substrates with varying binder content were tested and analyzed in order to assess coating adhesion and workpiece quality. Due to a reduction of cobalt binder within the tungsten carbide-based tool substrates, an increase of tool performance regarding borehole quantity until coating delamination is demonstrated. While the reduction of tool wear on the rake face of the drilling tools can be correlated with the cutting tool performance, the online monitoring of cutting forces does not explicitly identify damaged cutting tools during machining.
  • Publication
    Experimental observation of stress formation during selective laser melting using in situ X-ray diffraction
    ( 2020)
    Schmeiser, Felix
    ;
    Krohmer, Erwin
    ;
    Schell, Norbert
    ;
    Uhlmann, Eckart
    ;
    Reimers, Walter
    Despite the ongoing success of metal additive manufacturing and especially the selective laser melting (SLM) technology, process-related defects, distortions and residual stresses impede its usability for fracture-critical applications. In this paper, results of in situ X-ray diffraction experiments are presented that offer insights into the strain and stress formation during the manufacturing of multi-layer thin walls made from Inconel 625. Using different measuring modes and laser scanning parameters, several experimental observations are discussed to validate and extend theoretical models and simulations from the literature. As a sample is built-up layer by layer, the stress state changes continuously up until the last exposure. The localized energy input leads to a complex stress field around the heat source that involves alternating tensile and compressive stresses. The correlation of temperature and yield strength results in a stress maximum at a certain distance to the top layer. The present study demonstrates the potential of high-energy synchrotron radiation diffraction for in situ SLM research.
  • Publication
    A laser powder bed fusion system for in situ x-ray diffraction with high-energy synchrotron radiation
    ( 2020)
    Uhlmann, Eckart
    ;
    Krohmer, Erwin
    ;
    Schmeiser, Felix
    ;
    Schell, Norbert
    ;
    Reimers, Walter
    In Laser Powder Bed Fusion (LPBF), the highly localized energy input by the laser leads to high-temperature gradients. Combined with the inherent cycles of re-melting and solidification of the material, they can result in high mechanical stresses. These stresses can cause distortion and cracking within the component. In situ diffraction experiments with high-energy synchrotron radiation allow an analysis of the lattice spacing during the LPBF process and provide insight into the dynamics of stress generation and texture evolution. In this work, an LPBF system for the purpose of synchrotron x-ray diffraction experiments during the manufacturing process of multi-layer components with simple geometries is described. Moreover, results from diffraction experiments at the HEMS beamline P07 at PETRA III, DESY, Hamburg, Germany, are presented. Components with a length of ls = 20 mm and a width of ws = 2.5 mm consisting of 100 layers with a layer thickness of Dz = 50 µm were produced using the nickel-base alloy Inconel 625 as the powder material. Diffraction experiments were carried out in situ at sampling rates of f = 10 Hz with a synchrotron radiation beam size of 750 × 70 µm2. The presented experimental setup allows for the observation of arbitrary measuring positions in the sample in the transmission mode while gathering full diffraction rings. Thus, new possibilities for the observation of the dynamic evolution of strains, stresses, and textures during the LPBF process are provided.