In‐situ Observation of γ' Phase Transformation Dynamics during Selective Laser Melting of CMSX‐4
About: This article is published in Advanced Engineering Materials.The article was published on 2021-05-03 and is currently open access. It has received 5 citations till now. The article focuses on the topics: Selective laser melting & Phase (matter).
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TL;DR: In this article , the authors provide an overview of the research on metal PBF and DED using in-situ synchrotron X-ray imaging, diffraction and smallangle scattering, highlighting the state of the art, the instrumentation, the challenges and the gaps in knowledge that need to be filled.
11 citations
TL;DR: In this article , a review of the evolution of Ni-based superalloy microstructures during powder bed fusion (PBF) processes is presented, with an expressed goal of directing the research community toward the tools necessary for a thorough investigation of the processing-microstructure-property relationships in PBFNi-based microalloy parts to enable microstructural engineering.
Abstract: Abstract Metal additive manufacturing (AM) has unlocked unique opportunities for making complex Ni-based superalloy parts with reduced material waste, development costs, and production lead times. Considering the available AM methods, powder bed fusion (PBF) processes, using either laser or electron beams as high energy sources, have the potential to print complex geometries with a high level of microstructural control. PBF is highly suited for the development of next generation components for the defense, aerospace, and automotive industries. A better understanding of the as-built microstructure evolution during PBF of Ni-based superalloys is important to both industry and academia because of its impacts on mechanical, corrosion, and other technological properties, and, because it determines post-processing heat treatment requirements. The primary focus of this review is to outline the individual phase formations and morphologies in Ni-based superalloys, and their correlation to PBF printing parameters. Given the hierarchal nature of the microstructures formed during PBF, detailed descriptions of the evolution of each microstructural constituent are required to enable microstructure control. Ni-based superalloys microstructures commonly include γ, γ′, γ′′, $$\delta$$ δ , TCP, carbides, nitrides, oxides, and borides, dependent on their composition. A thorough characterization of these phases remains challenging due to the multi-scale microstructural hierarchy alongside with experimental challenges related to imaging secondary phases that are often nanoscale and (semi)-coherent. Hence, a detailed discussion of advanced characterization techniques is the second focus of this review, to enable a more complete understanding of the microstructural evolution in Ni-based superalloys printed using PBF. This is with an expressed goal of directing the research community toward the tools necessary for a thorough investigation of the processing-microstructure-property relationships in PBF Ni-based superalloy parts to enable microstructural engineering.
10 citations
TL;DR: In this article, high-energy X-ray diffraction experiments were carried out to illuminate the formation and evolution of microstructural features during laser powder bed fusion, and the diffraction patterns yielded results regarding texture, lattice defects, recrystallization, and chemical segregation.
Abstract: 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.
10 citations
3 citations
TL;DR: In this article , the influence of substrate pre-heating and a complex scan pattern on the strain and internal stress progression during the manufacturing of Inconel 625 parts is investigated, and phase transitions during melting and solidification of an intermetallic γ-TiAl based alloy are examined.
Abstract: The high flux combined with the high energy of the monochromatic synchrotron radiation available at modern synchrotron facilities offers vast possibilities for fundamental research on metal processing technologies. Especially in the case of laser powder bed fusion (LPBF), an additive manufacturing technology for the manufacturing of complex-shaped metallic parts, in situ methods are necessary to understand the highly dynamic thermal, mechanical, and metallurgical processes involved in the creation of the parts. At PETRA III, Deutsches Elektronen-Synchrotron, a customized LPBF system featuring all essential functions of an industrial LPBF system, is used for in situ x-ray diffraction research. Three use cases with different experimental setups and research questions are presented to demonstrate research opportunities. First, the influence of substrate pre-heating and a complex scan pattern on the strain and internal stress progression during the manufacturing of Inconel 625 parts is investigated. Second, a study on the nickel-base superalloy CMSX-4 reveals the formation and dissolution of γ' precipitates depending on the scan pattern in different part locations. Third, phase transitions during melting and solidification of an intermetallic γ-TiAl based alloy are examined, and the advantages of using thin platelet-shaped specimens to resolve the phase components are discussed. The presented cases give an overview of in situ x-ray diffraction experiments at PETRA III for research on the LPBF technology and provide information on specific experimental procedures.
2 citations
References
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TL;DR: It is shown how advanced thermodynamic calculations have become more accessible since: - A more user-friendly windows version of Thermo-Calc, TCW, has been developed, and there is an increasing amount of thermodynamic databases for different materials available.
Abstract: Software for calculation of phase diagrams and thermodynamic properties have been developed since the 1970's. Software and computers have now developed to a level where such calculations can be used as tools for material and process development. In the present paper some of the latest software developments at Thermo-Calc Software are presented together with application examples. It is shown how advanced thermodynamic calculations have become more accessible since: - A more user-friendly windows version of Thermo-Calc, TCW, has been developed. - There is an increasing amount of thermodynamic databases for different materials available. - Thermo-Calc can be accessed from user-written software through several different programming interfaces are available which enables access to the thermodynamic software from a user-written software. Accurate data for thermodynamic properties and phase equilibria can then easily be incorporated into software written in e.g. C++, Matlab and FORTRAN. Thermo-Calc Software also produces DICTRA, a software for simulation of diffusion controlled phase transformations. Using DICTRA it is possible to simulate processes such as homogenization, carburising, microsegregation and coarsening in multicomponent alloys. The different models in the DICTRA software are briefly presented in the present paper together with some application examples.
3,186 citations
TL;DR: In this article, a review of the relationship between process characteristics, material consolidation and the resulting materials and component properties is presented, with a special focus on the relationship of process characteristics and material consolidation.
Abstract: Selective electron beam melting (SEBM) belongs to the additive manufacturing technologies which are believed to revolutionise future industrial production. Starting from computer-aided designed data, components are built layer by layer within a powder bed by selectively melting the powder with a high power electron beam. In contrast to selective laser melting (SLM), which can be used for metals, polymers and ceramics, the application field of the electron beam is restricted to metallic components since electric conductivity is required. On the other hand, the electron beam works under vacuum conditions, can be moved at extremely high velocities and a high beam power is available. These features make SEBM especially interesting for the processing of high-performance alloys. The present review describes SEBM with special focus on the relationship between process characteristics, material consolidation and the resulting materials and component properties.
642 citations
TL;DR: The high-speed synchrotron hard X-ray imaging and diffraction techniques used to monitor the laser powder bed fusion (LPBF) process of Ti-6Al-4V in situ and in real time demonstrate that many scientifically and technologically significant phenomena in LPBF, including melt pool dynamics, powder ejection, rapid solidification, and phase transformation, can be probed with unprecedented spatial and temporal resolutions.
Abstract: We employ the high-speed synchrotron hard X-ray imaging and diffraction techniques to monitor the laser powder bed fusion (LPBF) process of Ti-6Al-4V in situ and in real time. We demonstrate that many scientifically and technologically significant phenomena in LPBF, including melt pool dynamics, powder ejection, rapid solidification, and phase transformation, can be probed with unprecedented spatial and temporal resolutions. In particular, the keyhole pore formation is experimentally revealed with high spatial and temporal resolutions. The solidification rate is quantitatively measured, and the slowly decrease in solidification rate during the relatively steady state could be a manifestation of the recalescence phenomenon. The high-speed diffraction enables a reasonable estimation of the cooling rate and phase transformation rate, and the diffusionless transformation from β to α
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phase is evident. The data present here will facilitate the understanding of dynamics and kinetics in metal LPBF process, and the experiment platform established will undoubtedly become a new paradigm for future research and development of metal additive manufacturing.
490 citations
TL;DR: A mechanism map for predicting the evolution of melt features, changes in melt track morphology from a continuous hemi-cylindrical track to disconnected beads with decreasing linear energy density and improved molten pool wetting with increasing laser power is developed.
Abstract: The laser–matter interaction and solidification phenomena associated with laser additive manufacturing (LAM) remain unclear, slowing its process development and optimisation. Here, through in situ and operando high-speed synchrotron X-ray imaging, we reveal the underlying physical phenomena during the deposition of the first and second layer melt tracks. We show that the laser-induced gas/vapour jet promotes the formation of melt tracks and denuded zones via spattering (at a velocity of 1 m s−1). We also uncover mechanisms of pore migration by Marangoni-driven flow (recirculating at a velocity of 0.4 m s−1), pore dissolution and dispersion by laser re-melting. We develop a mechanism map for predicting the evolution of melt features, changes in melt track morphology from a continuous hemi-cylindrical track to disconnected beads with decreasing linear energy density and improved molten pool wetting with increasing laser power. Our results clarify aspects of the physics behind LAM, which are critical for its development. Additive manufacturing of metals is now widely available, but the interaction of the metal powder with the laser remains unclear. Here, the authors use X-rays to image melt features and pore behaviour during laser melting of powders.
468 citations
TL;DR: In situ X-ray imaging and finite element simulations are used to show how detrimental pores form under printing conditions and develop a strategy to suppress them and provide insight into the physics of laser-metal interaction.
Abstract: Laser powder bed fusion additive manufacturing is an emerging 3D printing technique for the fabrication of advanced metal components. Widespread adoption of it and similar additive technologies is hampered by poor understanding of laser-metal interactions under such extreme thermal regimes. Here, we elucidate the mechanism of pore formation and liquid-solid interface dynamics during typical laser powder bed fusion conditions using in situ X-ray imaging and multi-physics simulations. Pores are revealed to form during changes in laser scan velocity due to the rapid formation then collapse of deep keyhole depressions in the surface which traps inert shielding gas in the solidifying metal. We develop a universal mitigation strategy which eliminates this pore formation process and improves the geometric quality of melt tracks. Our results provide insight into the physics of laser-metal interaction and demonstrate the potential for science-based approaches to improve confidence in components produced by laser powder bed fusion. Laser-matter interactions during laser powder bed fusion additive manufacturing remain poorly understood. Here, the authors combine in situ X-ray imaging and finite element simulations to show how detrimental pores form under printing conditions and develop a strategy to suppress them.
377 citations