In situ investigation of the rapid solidification behavior of intermetallic γ-TiAl-based alloys using high-energy X-ray diffraction
About: This article is published in Advanced Engineering Materials.The article was published on 2021-07-03 and is currently open access. It has received 5 citations till now. The article focuses on the topics: Intermetallic.
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TL;DR: In this paper , the authors proposed a counterintuitive strategy to mitigate cold cracking, by taking advantage of the high cooling rate rather than suppressing it, which led to the formation of a massive ductile β phase.
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
TL;DR: In this article , high-energy X-ray diffraction was employed to investigate how this thermodynamic equilibration manifested itself in the resulting phase distribution, the ordering behavior of the disordered α and β phase, both evidenced in the powder, and the change of the γ lattice parameters during heating of a Ti-46.3Al-2.2W−0.2B powder up to 850°C.
Abstract: Powder production by gas atomization of γ‐TiAl based alloys typically yields a highly nonequilibrium material regarding the occurring phases and their microstructural appearance. In particular, the equilibration of the powder and the associated phase transformations during heating are of great importance for the subsequently applied densification techniques. The present work employs in situ high‐energy X‐ray diffraction to investigate how this thermodynamic equilibration manifests itself in the resulting phase distribution, the ordering behavior of the disordered α and β phase, both evidenced in the powder, and the change of the γ lattice parameters during heating of a Ti–46.3Al–2.2W–0.2B (at%) powder up to 850 °C. Complementary microstructural characterization of the gas‐atomized powder and the heat‐treated material condition reveals that the temperature exposure predominately affects the dendritic parts of the microstructure, especially when the α phase is transformed into γ phase with small embedded grains of α2 and βo.
TL;DR: In this article , the Nb and B nanoparticles modified TiAl4822 composite powder with a nominal composition of Ti-47.53Al-1.98Cr-2.81Nb-0.15B were prepared via ball milling.
Abstract: Ball milling treatment is a low-cost and achievable large-scale production method for preparing the composite powder used for the laser powder bed fusion (LPBF) process. For the ball-milled composite powder, good powder spreadability and composition homogeneity are essential for obtaining the LPBF-fabricated part with good forming quality. In this article, the Nb and B nanoparticles modified TiAl4822 composite powder with a nominal composition of Ti-47.53Al-1.98Cr-2.81Nb-0.15B are prepared via ball milling. It is found that the physical properties of the composite powder are more sensitive to the milling time than the milling speed and ball-to-powder ratio. Long-time milling is inclined to cause the formation of broken particles, poor powder flowability, and high oxygen contamination. Besides, the process maps between the ball milling energy E t and particle size distribution width, the static angle of repose, composition inhomogeneity, and oxygen content are established, respectively. Results show that when the applied E t is insufficient or excessive, the degree of sphericity or composition homogeneity always worsens. In these cases, deposition defects such as line or area defects are more prone to occur, due to the enhanced particle rearrangement resistance induced by the addition of nanoparticles.
TL;DR: In this article , a high-frequency thermal cycling was designed to control the solid-state phase transformations in layer-by-layer additive manufacturing (AM) for fine-grain titanium aluminide alloys.
References
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TL;DR: In this paper, a structure refinement method was described which does not use integrated neutron powder intensities, single or overlapping, but employs directly the profile intensities obtained from step-scanning measurements of the powder diagram.
Abstract: A structure refinement method is described which does not use integrated neutron powder intensities, single or overlapping, but employs directly the profile intensities obtained from step-scanning measurements of the powder diagram. Nuclear as well as magnetic structures can be refined, the latter only when their magnetic unit cell is equal to, or a multiple of, the nuclear cell. The least-squares refinement procedure allows, with a simple code, the introduction of linear or quadratic constraints between the parameters.
14,360 citations
TL;DR: Calibration methods and software have been developed for single crystal diffraction experiments, using both approaches for calibrate, and apply corrections, to obtain accurate angle and intensity information.
Abstract: Detector systems introduce distortions into acquired data. To obtain accurate angle and intensity information, it is necessary to calibrate, and apply corrections. Intensity non-linearity, spatial distortion, and non-uniformity of intensity response, are the primary considerations. It is better to account for the distortions within scientific analysis software, but often it is more practical to correct the distortions to produce ‘idealised’ data. Calibration methods and software have been developed for single crystal diffraction experiments, using both approaches. For powder diffraction experiments the additional task of converting a two-dimensional image to a one-dimensional spectrum is used to allow Rietveld analysis. This task may be combined with distortion correction to produce intensity information and error estimates. High-pressure experiments can introduce additional complications and place new demands on software. Flexibility is needed to be able to integrate different angular regions se...
4,426 citations
TL;DR: A set of general guidelines for structure refinement using the Rietveld (whole profile) method has been formulated by the International Union of Crystallography Commission on Powder Diffraction.
Abstract: A set of general guidelines for structure refinement using the Rietveld (whole-profile) method has been formulated by the International Union of Crystallography Commission on Powder Diffraction. The practical rather than the theoretical aspects of each step in a typical Rietveld refinement are discussed with a view to guiding newcomers in the field. The focus is on X-ray powder diffraction data collected on a laboratory instrument, but features specific to data from neutron (both constant-wavelength and time-of-flight) and synchrotron radiation sources are also addressed. The topics covered include (i) data collection, (ii) background contribution, (iii) peak-shape function, (iv) refinement of profile parameters, (v) Fourier analysis with powder diffraction data, (vi) refinement of structural parameters, (vii) use of geometric restraints, (viii) calculation of e.s.d.'s, (ix) interpretation of R values and (x) some common problems and possible solutions.
1,808 citations
TL;DR: In this article, a general survey of engineering γ-TiAl based alloys is given, but concentrates on β-solidifying alloys which show excellent hot-workability and balanced mechanical properties when subjected to adapted heat treatments.
Abstract: After almost three decades of intensive fundamental research and development activities, intermetallic titanium aluminides based on the ordered γ-TiAl phase have found applications in automotive and aircraft engine industry. The advantages of this class of innovative high-temperature materials are their low density and their good strength and creep properties up to 750 °C as well as their good oxidation and burn resistance. Advanced TiAl alloys are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments. The background of these heat treatments is at least twofold, i.e., concurrent increase of ductility at room temperature and creep strength at elevated temperature. This review gives a general survey of engineering γ-TiAl based alloys, but concentrates on β-solidifying γ-TiAl based alloys which show excellent hot-workability and balanced mechanical properties when subjected to adapted heat treatments. The content of this paper comprises alloy design strategies, progress in processing, evolution of microstructure, mechanical properties as well as application-oriented aspects, but also shows how sophisticated ex situ and in situ methods can be employed to establish phase diagrams and to investigate the evolution of the micro- and nanostructure during hot-working and subsequent heat treatments.
791 citations
15 May 1999-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors examined gamma titanium-aluminide alloys, from the perspective of their balance of engineering properties, state of maturity, and prospects for impacting industrial needs.
Abstract: In the late 1970s and early 1980s, intermetallic phases emerged from being alloys of laboratory curiosity, or precipitate structures to be avoided or controlled in many ‘real metals’, to being widely investigated alloys, especially as prospective structural materials. After nearly two decades of sustained world-wide research, selected materials are emerging with a balance of properties which improves engineered systems, while others are introducing compelling research questions and prospects for significantly improved materials. This manuscript briefly examines selected intermetallic alloys and how they compete with other structural materials. The examination focuses on gamma titanium–aluminide alloys, from the perspective of their balance of engineering properties, state of maturity, and prospects for impacting industrial needs. A variety of engineering and business challenges remain to be solved, some of which are discussed.
484 citations