Solid-State Transformation of an Additive Manufactured Inconel 625 Alloy at 700 °C
17 Sep 2021-Applied Sciences (Multidisciplinary Digital Publishing Institute)-Vol. 11, Iss: 18, pp 8643
TL;DR: In this paper, the authors used synchrotron-based in situ scattering and diffraction methods and ex situ electron microscopy to investigate the solid-state transformation of an AM Inconel 625 at 700 °C.
Abstract: Inconel 625, a nickel-based superalloy, has drawn much attention in the emerging field of additive manufacturing (AM) because of its excellent weldability and resistance to hot cracking. The extreme processing condition of AM often introduces enormous residual stress (hundreds of MPa to GPa) in the as-fabricated parts, which requires stress-relief heat treatment to remove or reduce the internal stresses. Typical residual stress heat treatment for AM Inconel 625, conducted at 800 °C or 870 °C, introduces a substantial precipitation of the δ phase, a deleterious intermetallic phase. In this work, we used synchrotron-based in situ scattering and diffraction methods and ex situ electron microscopy to investigate the solid-state transformation of an AM Inconel 625 at 700 °C. Our results show that while the δ phase still precipitates from the matrix at this temperature, its precipitation rate and size at a given time are both smaller when compared with their counterparts during typical heat treatment temperatures of 800 °C and 870 °C. A comparison with thermodynamic modeling predictions elucidates these experimental findings. Our work provides the rigorous microstructural kinetics data required to explore the feasibility of a promising lower-temperature stress-relief heat treatment for AM Inconel 625. The combined methodology is readily extendable to investigate the solid-state transformation of other AM alloys.
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29 Nov 2021
TL;DR: In this paper, the same authors used both in-house X-ray diffraction and electron backscatter diffraction (EBSD) to characterize nitrogen-atomized 17-4 precipitation-hardening martensitic stainless steel.
Abstract: Accurate phase fraction analysis is an essential element of the microstructural characterization of alloys and often serves as a basis to quantify effects such as heat treatment or mechanical deformation. Additive manufacturing (AM) of metals, due to the intrinsic nonequilibrium solidification and spatial variability, creates additional challenges for the proper quantification of phase fraction. Such challenges are exacerbated when the alloy itself is prone to deformation-induced phase transformation. Using commonly available in-house X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) and less commonly used synchrotron-based high-energy X-ray diffraction, we characterized nitrogen-atomized 17-4 precipitation-hardening martensitic stainless steel, a class of AM alloy that has received broad attention within the AM research community. On the same build, our measurements recovered the entire range of reported values on the austenite phase fractions of as-built AM 17-4 in literature, from ≈100% martensite to ≈100% austenite. Aided by Calphad simulation, our experimental findings established that our as-built AM 17-4 is almost fully austenitic and that in-house XRD and EBSD measurements are subject to significant uncertainties created by the specimen’s surface finish. Hence, measurements made using these techniques must be understood in their correct context. Our results carry significant implications, not only to AM 17-4 but also to AM alloys that are susceptible to deformation-induced structure transformation and suggest that characterizations with less accessible but bulk sensitive techniques such as synchrotron-based high energy X-ray diffraction or neutron diffraction may be required for proper understanding of these materials.
3 citations
01 Jan 2023
TL;DR: In this paper , the authors build a CALPHADCALPHAD-based ICMEICME framework to investigate the microstructural stability and mechanical properties using the Thermo-Calc softwareThermo-calc software.
Abstract: The superalloySuperalloys INCONEL 718Inconel 718 stands out for its excellent manufacturability and strength at ambient temperature. In most recent studies people tried to improve the mechanical propertiesMechanical properties of the alloy through adjusting different processing conditions such as solution annealing temperature, agingAging temperature and holding time, and the amount of intermediate cold work. Such studies could be expensive and time consuming. This study aims to build a CALPHADCALPHAD-based ICMEICME framework to investigate the microstructural stabilityMicrostructural stability and mechanical propertiesMechanical properties using the Thermo-Calc softwareThermo-Calc software. The evolution of precipitates is characterized using the TC-PRISMA precipitationPrecipitation module paired with the TCNI12 and MOBNI6 databases. The microstructureMicrostructures is simulated in terms of the nucleation and growth of the precipitates. The precipitationPrecipitation of the secondary phasesSecondary phase $${\gamma }{\mathrm{{\prime}}}$$ , $$\gamma \mathrm{{\prime}}\mathrm{{\prime}}$$ and $$\delta $$ is simulated under different agingAging temperatures and their contributions to yield strengthYield strength are quantified. A simplified yield strengthYield strength model is applied to predict the precipitate, grain boundary and solid solution strengthening. The quantified results show good agreement with the experiment.
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TL;DR: A review of the emerging research on additive manufacturing of metallic materials is provided in this article, which provides a comprehensive overview of the physical processes and the underlying science of metallurgical structure and properties of the deposited parts.
4,192 citations
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: The approach to metal-based additive manufacturing is applicable to a wide range of alloys and can be implemented using a range of additive machines, and provides a foundation for broad industrial applicability, including where electron-beam melting or directed-energy-deposition techniques are used instead of selective laser melting.
Abstract: Metal-based additive manufacturing, or three-dimensional (3D) printing, is a potentially disruptive technology across multiple industries, including the aerospace, biomedical and automotive industries. Building up metal components layer by layer increases design freedom and manufacturing flexibility, thereby enabling complex geometries, increased product customization and shorter time to market, while eliminating traditional economy-of-scale constraints. However, currently only a few alloys, the most relevant being AlSi10Mg, TiAl6V4, CoCr and Inconel 718, can be reliably printed; the vast majority of the more than 5,500 alloys in use today cannot be additively manufactured because the melting and solidification dynamics during the printing process lead to intolerable microstructures with large columnar grains and periodic cracks. Here we demonstrate that these issues can be resolved by introducing nanoparticles of nucleants that control solidification during additive manufacturing. We selected the nucleants on the basis of crystallographic information and assembled them onto 7075 and 6061 series aluminium alloy powders. After functionalization with the nucleants, we found that these high-strength aluminium alloys, which were previously incompatible with additive manufacturing, could be processed successfully using selective laser melting. Crack-free, equiaxed (that is, with grains roughly equal in length, width and height), fine-grained microstructures were achieved, resulting in material strengths comparable to that of wrought material. Our approach to metal-based additive manufacturing is applicable to a wide range of alloys and can be implemented using a range of additive machines. It thus provides a foundation for broad industrial applicability, including where electron-beam melting or directed-energy-deposition techniques are used instead of selective laser melting, and will enable additive manufacturing of other alloy systems, such as non-weldable nickel superalloys and intermetallics. Furthermore, this technology could be used in conventional processing such as in joining, casting and injection moulding, in which solidification cracking and hot tearing are also common issues.
1,670 citations
TL;DR: In this article, a unified approach to the analysis of small-angle scattering is presented that describes scattering from complex systems that contain multiple levels of related structural features, such as the overall radius of gyration and the substructural persistence length.
Abstract: A new approach to the analysis of small-angle scattering is presented that describes scattering from complex systems that contain multiple levels of related structural features. For example, a mass fractal such as a polymer coil contains two structural levels, the overall radius of gyration and the substructural persistence length. One structural level is described by a Guinier and an associated power-law regime. A function is derived that models both the Guinier exponential and structurally limited power-law regimes without introducing new parameters beyond those used in local fits. Account is made for both a low-q and a high-q limit to power-law scattering regimes. The unified approach can distinguish Guinier regimes buried between two power-law regimes. It is applicable to a wide variety of systems. Fits to data containing multiple power-law and exponential regimes using this approach have previously been reported. Here, arguments leading to the unified approach are given. The usefulness of this approach is demonstrated through comparison with model calculations using the Debye equation for polymer coils (mass fractal), equations for polydisperse spheres (Porod scattering) and randomly oriented ellipsoids of revolution with diffuse interfaces, as well as randomly oriented rod and disc-shaped particles.
1,243 citations
TL;DR: In this article, the precipitation of the metastable δ-Ni3Nb phase has been studied in two niobium bearing nickel base superalloys and the morphology and distribution of precipitates have been examined and the crystallographic orientation relationship between the austenite and the δ phases has been determined.
Abstract: The precipitation of the equilibrium δ-Ni3Nb phase has been studied in two niobium bearing nickel base superalloys—INCONEL 718 and INCONEL* 625—both of which are hardenable by the precipitation of the metastableγ″-Ni3Nb phase. The morphology and the distribution of precipitates have been examined and the crystallographic orientation relationship between the austenite and theδ phases has been determined. The nucleation of theδ phase at stacking faults within pre-existing δ" precipitates has been discussed.
383 citations