Showing papers by "Carolin Körner published in 2019"

Creep properties of single crystal Ni-base superalloys (SX): A comparison between conventionally cast and additive manufactured CMSX-4 materials

Abstract: The present work compares the microstructures and the creep properties of two types of single crystal Ni-base superalloy CMSX-4 materials (SXs). One was produced by conventional directional solidification Bridgman processing. The other was manufactured by selective electron beam melting (SEBM). The microstructures of the two types of materials are compared with emphasis placed on the large (dendritic/interdendritic regions) and small scale (γ-matrix/γ′-precipitates) microstructural heterogeneities, which characterize SX microstructures and their evolution during processing, heat treatment and creep. It is shown that heat treated SEBM materials have creep properties, which match or even outperform those of conventionally processed SX materials. Creep properties were assessed using a miniature creep test technique where [001] miniature tensile creep specimens were tested in the high temperature/low stress (1050 °C, 160 MPa) and in the low temperature/high stress (850 °C, 600 MPa) creep regimes. The creep behavior is interpreted based on microstructural results, which were obtained using analytical scanning and transmission electron microscopy (SEM and TEM).

Predictive simulation of process windows for powder bed fusion additive manufacturing: Influence of the powder size distribution

Abstract: The properties of parts fabricated by powder bed fusion additive manufacturing depend on the process strategy as well as the characteristics of the powder bed. The aim of this study is to determine the influence of different powder size distributions for certain process parameters taken from a process window for Ti–6Al–4V. All results are obtained from our in-house software S AM PLE 2D . The first objective is identifying layer binding faults causing porous structures. We demonstrate the influence of surface roughness of each single layer for single- and multi-layer binding faults and the consequences for process windows. The second objective is the investigation of the final sample roughness. Generally, a minimal surface roughness is aimed to reduce the post-processing effort for surface finishing. By combining the findings regarding porosity and sample surface roughness, we conclude that powder size distributions with larger mean particle diameter generally diminish the process reliability and increase the required energy input.

Impact of build envelope on the properties of additive manufactured parts from AlSi10Mg

Abstract: The selective laser melting (SLM) process is well established in the construction of prototypes and in the low volume production. With increasing build-up rates the next step to serial production is possible. Multi laser systems and larger build envelopes make the process cost-efficient. Enlarged systems enable not only the manufacturing of numerous smaller parts in one build job but also bigger parts for the automotive and aerospace industry. A modified metal laser melting machine X LINE 2000R equipped with a dual laser system and an enlarged build envelope is used to investigate the position-dependent properties of parts made from AlSi10Mg. The impact on porosity and mechanical properties is shown for different spatial directions. The results are an important contribution to process design, component layout and further improvements of larger SLM machines.

Formation of topologically closed packed phases within CMSX-4 single crystals produced by additive manufacturing

Abstract: The homogeneity of single crystals produced by additive manufacturing (AM) is much higher than that of single crystals produced by the standard investment casting process. Aim of this paper is to investigate the influence of this homogeneity on the formation kinetics of topologically closed packed (TCP) phases. CMSX-4 single crystals produced by selective electron beam melting and investment casting are homogenized and annealed at 870 °C and 1050 °C for up to 480 h. The formation kinetics of TCP phase formation is analyzed by electron microscopy.

Grain Structure Evolution of Al-Cu Alloys in Powder Bed Fusion with Laser Beam for Excellent Mechanical Properties.

Abstract: Powder Bed Fusion with Laser Beam of Metals (PBF-LB/M) is one of the fastest growing technology branches. More and more metallic alloys are being qualified, but processing of aluminum wrought alloys without cracks and defects is still challenging. It has already been shown that small parts with low residual porosity can be produced. However, suffering from microscopic hot cracks, the fracture behavior has been rather brittle. In this paper different combinations of temperature gradients and solidification rates are used to achieve specific solidification conditions in order to influence the resulting microstructure, as well as internal stresses. By this approach it could be shown that EN AW-2024, an aluminum-copper wrought alloy, is processable via PBF-LB/M fully dense and crack-free with outstanding material properties, exceeding those reported for commonly manufactured EN AW-2024 after T4 heat treatment.

Processing windows for Ti-6Al-4V fabricated by selective electron beam melting with improved beam focus and different scan line spacings

Abstract: Selective electron beam melting (SEBM) is a highly versatile powder bed fusion additive manufacturing method. SEBM is characterized by high energy densities which can be applied with nearly inertia free beam deflection at high speeds (<8.000 m/s). This paper aims to determine processing maps for Ti-6Al-4V on an Arcam Q10 machine with LaB6 cathode design.,Scan line spacings of 100, 50 and 20 µm in a broad parameter range, focusing on high deflection and build speeds are investigated.,There are broad processing windows for dense parts without surface flaws for all scan line spacings which are defined by the total energy input and the area melting velocity.,The differences and limitations are discussed taking into account the beam properties at high beam energy and velocity as well as evaporation related loss of alloying components.

In situ Al3Ti/Al composites fabricated by high shear technology: microstructure and mechanical properties

Abstract: In situ Al3Ti/Al composites were produced by the reaction between Ti powder and Al melt with high shear technology. As Ti powder is starting material, it is important to investigate its siz...

Advanced process strategy to realize microducts free of powder using selective electron beam melting

Abstract: Selective electron beam melting (SEBM) is a powder bed–based additive manufacturing (AM) technology and allows the fabrication of complex metal components. However, the high building temperatures necessary for a stable process prohibit the fabrication of small internal features and intended cavities, e.g., for cooling purposes and heat exchangers. In this work, a novel scan strategy is used to seal prefabricated notches on the surface of Ti-6Al-4V substrates and to create microducts without applying additional materials. Influencing factors are identified and a process map for the SEBM sealing process is established. The impact of the determined strategy on the material properties regarding surface structure and composition is investigated. This sealing process can be followed by conventional SEBM-based additive manufacturing to build complex structures on the sealing layer due to its high flatness.

3D Printed Copper Waveguides by Selective Electron Beam Melting Process for E-Band

Abstract: This work evaluates 3D printed E-Band waveguides by selective electron beam melting process with two different scanning pattern approaches. One is the contouring and the other the hatching pattern which are used to draw the waveguide cross section layer wise. The measured signal attenuation can be significantly reduced to only about $\alpha$ ≈ 11–17 dB/m in E-Band by applying the contour strategy despite the relatively large macroscopic RMS surface roughness of Rq ≳ 30 µm. Furthermore, a model based explanation for the measured results is proposed suggesting a distinct separation between microscopic structure geometry and surface roughness for E-Band frequencies and beyond.