Effect of microstructural features on deformation and fracture in additively manufactured metals
Allison M. Beese, Assistant Professor of Materials Science and Engineering and Mechanical Engineering, Pennsylvania State University, USA
The unique thermal histories (i.e., rapid solidification followed by repeated thermal cycles with the addition of layers) seen in additive manufacturing (AM) of metallic materials results in heterogeneous microstructures, which may contain elongated grains and internal pores, among other unique features. These microstructures result in anisotropic and heterogeneous mechanical properties. To enable the adoption of AM for structural applications, an understanding of the links between microstructure and deformation and/or fracture is required in order to safely and reliably design against failure. In this talk, I will present our work on experimentally and computationally investigating the impact of these unique microstructures on the deformation and failure behavior of additively manufactured metals. In particular, I will discuss our efforts in measuring and modeling the multiaxial plasticity and fracture behavior of these materials. Additionally, I will describe our work on characterizing the impact of internal pores, commonly found in AM, on the strength and fracture behavior of additively manufactured metals.
Allison Beese received a B.S. in Mechanical Engineering from Penn State University, and an M.S. and Ph.D. in Mechanical Engineering from the Massachusetts Institute of Technology. She performed postdoctoral research at Northwestern University before joining the faculty at Penn State in 2013.
Additive manufacturing of steels - alloy development aided by integrated computational materials engineering
Greta Lindwall, Assistant Professor, School of Industrial Engineering and Management, KTH Royal Institute of Technology, Stockholm, Sweden
The interest in powder-based additive manufacturing (AM) of steels in Sweden has increased rapidly in recent years motivated by Sweden being a major metal powder producer and having a long tradition of advanced steel development. Although many of the computational methods available for steel design are applicable also for the development of AM grades, there are certain aspects of the AM processes that will require new models and computational approaches.
This work emphasizes how available models can be adapted to fit the AM processes and identifies areas for which new models and design strategies are required. Starting from the powder microstructure - via the as-built microstructure - to the effect of post-heat treatments, we integrate experimental characterizations with computational thermodynamics and kinetics based on the CALPHAD method to increase the understanding and predictability of the microstructural evolution. The approach is demonstrated through examples of our ongoing research activities on additively manufactured steels including tool steels and ferritic stainless steels. In particular, the computational approach to study the effects of composition, micro-segregation and thermal history on martensite formation is presented. Moreover, modeling approaches for controlled solidification and grain growth during printing are discussed.
Development of advanced Ni-base superalloys for additive manufacturing: relationship between microstructure and mechanical properties
Johan Moverare, Professor and Head of division in Engineering Materials, Linköping University, Linköping, Sweden
Further development and increased efficiency of gasturbines can be achieved by advances in nickel-based superalloys and manufacturing methods, including the adoption of additive manufacturing. However, high-performance Ni-base superalloys with excellent creep and oxidation resistance have been found very difficult to process by additive manufacturing (AM) without significant cracking issues. This is connected to the materials response to the rapid melting and solidification nature of the AM process. In order to assure successful introduction of new high-performance Ni-base superalloys into AM, tailoring of the alloy powder composition is needed in combination with the AM process parameters optimization and adoption of appropriate post-AM processes.
Cracking of y' (gamma)-strengthened Ni-base superalloys is commonly observed during additive manufacturing and the frequency of cracks depend on several different things such as major element composition (mainly Al, Ti), minor element compositions (like Si, Zr, B, C) and process parameters. Most likely these effects are also interacting making it difficult to transfer knowledge from one alloy to another. The key to understand this cracking phenomenon is to have control of the residual stresses introduced during the building process and the grain boundary character, i.e. the orientation difference between the grains, influence of intergranular precipitates and segregation of elements.
When it comes to the mechanical properties, the fundamental correlations between processing parameters to defect tendency and microstructure evolution must be well understood. Only by selecting an appropriate powder composition, optimized processing parameters and suitable post-processing methods the microstructure and the mechanical properties of the final part can be tailored successfully. In this presentation a review of the advances and opportunities in the development of additive manufacturing of advanced Nickel-based superalloys will be given.
Johan Moverare is Professor and Head of division in Engineering Materials at Linköping University. He is also a work package leader within the Centre for Additive Manufacture – Metal, CAM2. Main research focus is the relationship between microstructure and mechanical properties of metallic materials, especially fatigue and creep properties of high temperature alloys, such as Ni-base superalloys. He also has more than 10 years of industrial experience work at Siemens Industrial Turbomachinery as specialist in Superalloys.
Alloys for Electron Beam Melting (EBM)
Burghardt Klöden, Dr., Group Manager Additive Manufacturing - Electron Beam Melting, Fraunhofer Institute for Manufacturing Technology and Advanced Materials, Dresden, Germany
Electron Beam Melting (EBM) is a powder bed fusion AM process, which uses the electron beam as energy source to build parts layer-by-layer. It is characterized by elevated process temperatures and the process atmosphere, which is vacuum. The presentation will summarize the contribution of Fraunhofer IFAM to process and powder development with respect to alloys for EBM. The focus will be on steels (e.g. stainless, duplex, tool steel). Alloy-specific details concerning the processing by EBM will be explained and compared. Concerning powder, the EBM process was observed to be robust with respect to changes in powder properties. Powder bed temperature ranged from 800 °C in austenitic stainless steels to 950 °C in the tool steel CP2M. The highest build rates of 30 cm3/h were achieved for 316L, while crack-sensitive materials were slower to build.
On selected examples, results like the microstructure in as-built or heat-treated state and mechanical properties will be shown. In 316L a unique microstructure was observed and the tensile strength and ductility matched that of rolled material. In other materials a very fine carbide distribution and uniform hardness suitable for fabrication of molds and cutting tools was found.
In addition to that, selected results of materials like e.g. copper or titanium aluminide will be part of this overview. Furthermore, case studies on prototypical parts covering the range of EBM-processed materials will be included as well.
Burghardt Kloeden graduated as »Dipl.-Phys.« in physics from Dresden University of Technology, Germany, and University of Sheffield, UK, in 2002. In 2006, Burghardt obtained his »Dr. rer. nat.« (PhD) degree from TU Dresden, Faculty of Natural Sciences. He has joined the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM as a scientific researcher in 2006, where he helped establishing »Additive Manufacturing by Electron Beam Melting« as a new field of research and has been managing this as the responsible Group Manager since 2016.
Burghardt has recurrently worked with additive manufacturing / 3D printing technologies for more than 5 years, focussing now on electron beam melting technology (metal 3D printing) and aspects of powder for additive manufacturing. Burghardt has authored 20+ technical and scientific publications and presented also 30+ technical papers at national and international conferences, symposia and workshops.
Additive manufacture 4.0: Using in-process data to control component integrity and microstructure
Iain Todd, Professor of Metallurgy, Director MAPP EPSRC Future Manufacturing Hub, GKN/Royal Academy of Engineering Research Chair Additive Manufacturing, Department of Materials Science and Engineering, The University of Sheffield
Alloy Development for Metal AM
Ola L. A. Harrysson, Edward P. Fitts Distinguished Professor, Co-Director of CAMAL, Department of Industrial & Systems Engineering, North Carolina State University, USA
Metal AM is quickly growing but one of the limiting factors is the few number of alloys available for the powder bed fusion processes. The research team at NC State University, Raleigh, NC USA, have spent over 15 years developing process parameters for new alloys. The two processes that have been used so far are Electron Beam Melting (EBM) and Selective Laser Melting (SLM). The team has developed a standard procedure that is followed for each new material. This presentation will highlight some of the successes and some of the failures that have been accomplished over the years. Further, new alloy development for metal AM will be discussed.
Dr. Ola L. A. Harrysson joined the ISE Department at NC State University in Raleigh, North Carolina in 2002 after receiving his Ph.D. in Industrial Engineering from the University of Central Florida in Orlando, Florida. Prior to attending UCF he was born and raised in Sweden and received his bachelor’s degree in Mechanical Engineering from Dala University.
He has been conducting research in Additive Manufacturing for over 20 years. His main areas of research are medical application of AM technologies, custom design and fabrication of orthopedic implants, medical device development, and materials development for Direct Metal AM technologies. Dr. Harrysson is the Co-Director of the Center for Additive Manufacturing and Logistics at NCSU. Dr. Harrysson is the Edward P. Fitts Distinguished Professor in the Edward P. Fitts Department of Industrial Engineering. He has affiliated appointments in the Departments of Biomedical Engineering and Material Science and Engineering.
The role of alloys and powders with respect to quality management in laser powder bed fusion
Adriaan B. Spierings, Dr., Head R&D SLM, inspire AG – Innovation Centre for Additive Manufacturing (icams), Switzerland
Metal additive manufacturing and specifically powder bed fusion (PBF) has reached a high level of maturity, and is being used for various high-quality industries, ranging from turbine industry to space & aerospace and medical applications. For such industries and applications quality management of processes and parts manufacturing is therefore of key interest. A quality management system however does not only address the quality control of the final products, but addresses the complete process chain from alloys, powders, their additive processing and related machines. In this respect appropriate alloy compositions and suitable powder formulations are of key interest in order to enable robust and productive processing windows, and high quality material and part properties.
On the alloy-side, the very specific processing conditions given during powder bed fusion are characterized by small melt-pool dimensions, very high cooling-rates and -gradients as-well as related geometry-dependent boundary conditions of the part under production. In addition, the cyclic heat treatment form the layer-wise build process gives rise to grain growth and recrystallization effects. Hence, dependent on the effective cooling rates the process inherent rapid solidification may result in solute trapping and phases are in non-equilibrium. These effects drive the formation of the respective alloy microstructure, being typically fine-grained and showing an alloy-specific texture and preferential grain growth in the build direction. Therefore, there is a growing need for the development of advanced alloy compositions dedicated to additive manufacturing, and where benefit is taken from the unique processing conditions. By that it is possible to minimize pore- or solidification crack formation, to optimize the resulting microstructure and mechanical properties, or to design completely new materials that are not possible with conventional manufacturing routes.
On the powder-side, the powder properties also affect the processing conditions, and by this the properties of the consolidated materials. Not only flowability aspects play an important role, but also the particle size distribution, as these affect the powder layer density, and related layer thickness.
The presentation addresses basic powder related requirements, and discusses limitations and options for the development of advanced alloys for Laser-PBF. These requirements are set into the context of a quality management system for the AM-process chain.
A.Spierings studied mechanical engineering at ETH in Zurich with a focus on lightweight / aerospace engineering and business administration. Initially he was active in technical project controlling and business development, and since 2002 in research and development.
He has a PhD in additive manufacturing on “Powder spreadability and characterization of Sc- and Zr-modified Al-alloys processed by SLM”.
A.Spierings has been leading the SLM research group at inspire-innovation centre for additive manufacturing (icams) since 2005. The group focusses on quality management systems for AM, addressing hereby the complete processing chain from materials (powders, alloys), processes (simulation, monitoring) and machine components to industrial applications.
Mesoscopic Simulation for AM process development and microstructure design
Carolin Körner, Professor and Head to the Chair of Materials Science and Engineering for Metals, Friedrich-Alexander-University Erlangen-Nürnberg, Germany
Additive manufacturing (AM) is inducing some kind of next industrial revolution. Components develop layer by layer in a powder bed by selective beam melting according to 3D model data. This technique allows manufacturing of highly complex components and is especially interesting for high performance materials that are difficult to process in conventional technologies. Nevertheless, AM is challenged by material quality issues such as porosity, binding faults, surface roughness, selective evaporation, texture, etc.
In this contribution, the variety of physical phenomena important during powder bed based AM of metallic alloys is discussed based on mesoscopic simulation also taking into account the effect of individual powder particles. We show the influence of the powder properties, such as bulk density or size distribution, on the consolidation process and stochastic appearing faults. Examples show the influence of the processing parameters and the consolidation strategy on phenomena such as selective evaporation or texture evolution. In summary we show, how mesoscopic simulation improves process understanding and represents the basis for further process development.
PhD in the field of laser material interaction phenomena
Habilitation for Materials Science 2007 (FAU)
Since 2011: Head of the Chair Metals Science and Technology at the University of Erlangen-Nuremberg.
Since 2013: Head of the business area “Additive manufacturing” at New Material Fürth GmbH (Fürth)
Work areas: additive manufacturing, pressure die casting and investment casting, process modelling