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Special Issue "Additive Manufacturing of High Temperature Alloys"

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A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Additive Manufacturing".

Deadline for manuscript submissions: 20 March 2024 | Viewed by 9000

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Special Issue Editors

Dr. Vera Popovich

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Guest Editor

Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands
Interests: additive manufacturing; smart materials; mechanical behavior; damage and fracture of engineering materials
Special Issues, Collections and Topics in MDPI journals

Dr. Ehsan Hosseini

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Guest Editor

Empa, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600 Dübendorf, Switzerland
Interests: additive manufacturing; thermomechanical modeling; microstructure simulation; high-temperature alloys; creep; fatigue

Special Issue Information

Dear Colleagues,

High-temperature alloys, such as superalloys, are some of the most commonly employed alloys for metal additive manufacturing and have a wide range of applications in aircraft, gas turbines, turbocharger rotors, and a variety of other energy and aerospace applications.

Additive manufacturing (AM) is considered an attractive manufacturing technique for components with complex geometries due to the near-net shape production capability. Despite the many advantages of AM methods, including design flexibility, producing functionally graded parts, and a significantly lower buy-to-fly ratio, aspects such as the development of high residual stresses and, possibly, the formation of detrimental phases and defects in additively manufactured parts are a matter of concern. Thus, one of the main challenges preventing the widespread use of the AM method for the production of critical parts is the uncertainty in the resultant properties, such as quality, reproducibility, and predictability of mechanical and functional performance. AM process condition optimization and post-processing heat treatments are then often employed to reduce these detrimental effects and enhance the properties.

It is our pleasure to invite you to submit contributions that may take into account any of high-temperature alloy aspects involved in additive manufacturing. For this open-access Special Issue, we particularly welcome original research articles and review papers focused on (i) the relationship between AM process parameters, evolution of resulting microstructure, and functional properties; (ii) the effect of various heat treatments; (iii) mechanical performance and environmental effects (high temperature, hydrogen or corrosive environment); (iv) the development of functionally graded or multimaterials AM; (v) modeling and design for performance optimization; and (vi) powder and alloy design.

Dr. Vera Popovich
Dr. Ehsan Hosseini
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

high-temperature alloys
additive manufacturing (AM)
laser powder bed fusion (L-PBF)
electron beam powder bed fusion (EB-LBF), direct metal deposition (DMD), alloy and product design
post-process treatment
microstructural characterization
mechanical and functional properties
modeling

Published Papers (7 papers)

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Research

Open AccessArticle

Structure and Properties Evolution of AZhK Superalloy Prepared by Laser Powder Bed Fusion Combined with Hot Isostatic Pressing and Heat Treatment

and

Metals 2023, 13(8), 1397; https://doi.org/10.3390/met13081397 - 04 Aug 2023

Viewed by 377

Abstract

The structure and properties of samples obtained by the laser powder bed fusion (LPBF) method from the AZhK alloy, intended for the manufacture of heavily loaded body parts with operating temperatures up to 800 °C, have been studied. The optimal mode of LPBF, ensuring the attainment of the minimal residual porosity of 0.02%, was identified for the superalloy AZhK. Additionally, the evolution of the microstructure of LPBF samples after hot isostatic pressing (HIP) and heat treatment (HT) was studied using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The macrostructure of LPBF samples is represented by columnar grains oriented in the direction of predominant heat dissipation, perpendicular to the build plate. At the microlevel, the structure consists of colonies of columnar dendrites. Nb₄AlC₃ and Nb₆C₄ carbides, as well as the Mo₂Hf Laves phase, are precipitated in the interdendritic region as a result of doping element segregation. The low strength of the LPBF samples (σ = 967 ± 10 MPa) is caused by the fact that there are no reinforcing particles and by high internal stress due to high crystallization speed. HIP and HT were found to have a favorable effect on the structure and properties of the LPBF samples. The post-treatment resulted in uniform distribution of γ′-phase precipitates sized up to 250 nm in the matrix bulk and carbides at grain boundaries, as well as Laves phase dissolution. Therefore, the strength characteristics were significantly improved: by 45% at room temperature and by 50% at elevated temperatures. High strength and ductility were attained (at 20 °C, σ²⁰ = 1396 ± 22 MPa and δ = 19.0 ± 3.0 %; at 650 °C, σ⁶⁵⁰ = 1240 ± 25 MPa and δ = 15.8 ± 1.5%; at 750 °C, σ⁷⁵⁰ = 1085 ± 23 MPa and δ = 9.1 ± 2.3%). An ejector-type part was fabricated, and its geometric parameters coincided with those in the electronic models. After conducting computed tomography, it was found that there are no defects in the form of non-fusion and microcracks within the volume of the part; however, it was observed that the pore size is ≥20 μm. Full article

(This article belongs to the Special Issue Additive Manufacturing of High Temperature Alloys)

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Open AccessArticle

Effect of Laser Power on the Recrystallization Temperature of an Additively Manufactured IN718

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Metals 2023, 13(8), 1355; https://doi.org/10.3390/met13081355 - 28 Jul 2023

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Abstract

Over the past few decades, there has been much research on additive manufacturing in both the academic and the industrial spheres to overcome the limitations of conventional manufacturing methods, thereby enabling the production of complex designs for improved performance. To achieve this purpose, it is crucial to meticulously set suitable laser parameters within the context of microstructural characteristics, including type and fraction of defects, texture development, residual stress, and grain size, etc. In the present study, we focused on recrystallization behavior, a type of relaxation process for accumulated thermal stress during the L-PBF process, as a function of laser power applied on the L-PBF process. The laser power has significant effects on the amount of recrystallized grain, directly related to the recrystallization temperature. Within the range of laser power used in this study, a downward trend was observed in the recrystallization temperature as the laser power increased from 370 W to 390 W. This trend suggests that higher laser power leads to a faster cooling rate, influenced by the volume of melt pool as well as the amount of heat dissipation from the melt pool, resulting in higher thermal stress during the process. Full article

(This article belongs to the Special Issue Additive Manufacturing of High Temperature Alloys)

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Open AccessArticle

Microstructure and Mechanical Properties of Hastelloy X Fabricated Using Directed Energy Deposition

Yoon-Sun Lee

and

Ji-Hyun Sung

Metals 2023, 13(5), 885; https://doi.org/10.3390/met13050885 - 03 May 2023

Cited by 1 | Viewed by 1011

Abstract

Laser-aided additive manufacturing is used for complex shapes and Ni-based superalloy parts. This study aimed to optimize the additive manufacturing process of Hastelloy X alloy to obtain its excellent mechanical properties without pores or cracks in the additively manufactured parts. The additively manufactured Hastelloy X was analyzed by comparing porosity, microstructure, and mechanical properties in as-built and post-heat treatment conditions. In addition, the pores existing inside the as-built specimen considerably decreased after the hot isostatic press (HIP) treatment. Furthermore, cell/columnar microstructures were observed owing to a fast cooling rate in the as-built condition. However, after heat treatment, dendrite structures disappeared, and recrystallized equiaxed grains were observed. The tensile test results showed that there was mechanical anisotropy along the vertical and horizontal directions, and as the microstructure changed to equiaxed grains after heat treatment, the mechanical anisotropy decreased, and the high-temperature properties improved. Full article

(This article belongs to the Special Issue Additive Manufacturing of High Temperature Alloys)

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Open AccessArticle

Hydrogen Embrittlement of Inconel 718 Manufactured by Laser Powder Bed Fusion Using Sustainable Feedstock: Effect of Heat Treatment and Microstructural Anisotropy

Naveen Karuthodi Mohandas

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Metals 2023, 13(2), 418; https://doi.org/10.3390/met13020418 - 17 Feb 2023

Viewed by 1924

Abstract

This study investigated the in-situ gaseous (under 150 bar) hydrogen embrittlement behaviour of additively manufactured (AM) Inconel 718 produced from sustainable feedstock. Here, sustainable feedstock refers to the Inconel 718 powder produced by vacuum induction melting inert gas atomisation of failed printed parts or waste from CNC machining. All Inconel 718 samples, namely AM-as-processed, AM-heat-treated and conventional samples showed severe hydrogen embrittlement. Additionally, it was found that despite its higher yield strength (1462 ± 8 MPa) and the presence of δ phase, heat-treated AM Inconel 718 demonstrates 64% lower degree of hydrogen embrittlement compared to the wrought counterpart (Y.S. 1069 ± 4 MPa). This was linked to the anisotropic microstructure induced by the AM process, which was found to cause directional embrittlement unlike the wrought samples showing isotropic embrittlement. In conclusion, this study shows that AM Inconel 718 produced from recycled feedstock shows better hydrogen embrittlement resistance compared to the wrought sample. Furthermore, the unique anisotropic properties, seen in this study for Inconel 718 manufactured by laser powder bed fusion, could be considered further in component design to help minimise the degree of hydrogen embrittlement. Full article

(This article belongs to the Special Issue Additive Manufacturing of High Temperature Alloys)

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Open AccessArticle

Influence of Replacing Molybdenum with Tungsten on the Creep Fracture Property of Waspaloy Nickel-Based Alloy

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Metals 2022, 12(11), 1842; https://doi.org/10.3390/met12111842 - 28 Oct 2022

Cited by 1 | Viewed by 831

Abstract

Alloys meeting the requirements of “700 °C and above” advanced ultra-super-critical technology, with higher thermal efficiency, have been developed in recent years. Here, a new wrought Ni-based superalloy with excellent high-temperature creep strength based on Waspaloy has been developed and is proposed as a candidate material for application in 700 °C class advanced ultra-super-critical steam turbine blades. In this new alloy, the Molybdenum (Mo) in Waspaloy is partially replaced by Tungsten (W). Creep tests have shown that this new Ni-based alloy has a 70 MPa higher creep-rupture strength than that of Waspaloy at 700 °C by extrapolating the experimental data. Detailed creep-rupture mechanisms have been analyzed by means of scanning electron microscopy, transmission electron microscopy, and chemical phase analysis with a view to devising potential approaches for performance improvements. The results showed that the partial replacement of Mo by W had negligible effect on the composition of carbides precipitated in the alloy. Instead, the amount of the γ′ phase was significantly increased, and mismatch between the γ and γ′ phases was reduced. In this way, the stability of the γ′ phase was increased, its coarsening rate was reduced, and its critical shear stress was increased. As a result, the high-temperature creep-fracture strength of the new alloy was increased. Full article

(This article belongs to the Special Issue Additive Manufacturing of High Temperature Alloys)

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Open AccessArticle

Mechanical Properties and Fracture Behavior of Laser Powder-Bed-Fused GH3536 Superalloy

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Metals 2022, 12(7), 1165; https://doi.org/10.3390/met12071165 - 08 Jul 2022

Cited by 1 | Viewed by 1239

Abstract

Heat treatment (HT) is an important approach to tune the structure and mechanical properties of as-printed or hot-isostatic-pressed (HIPed) additive manufacturing materials. Due to the carbide precipitates extensively existing after HT with air cooling, this paper studies the microstructure and mechanical behavior of laser powder-bed-fused (L-PBFed) GH3536 superalloy with laminar carbide precipitates at grain boundaries. By comparing with air-cooling samples and water-quenched samples, the results revealed that air cooling often introduced precipitates at grain boundaries, which impede the plastic deformation and are prone to lead to severe transgranular cracks on the fracture surface, contributing to a higher strain-hardening rate but lower ductility of HTed sample. Water quench can largely eliminate the grain-boundary precipitates, contributing to an optimized ductility even with smaller grain size. This work provides more details on the precipitate-deformation relation after HT. Full article

(This article belongs to the Special Issue Additive Manufacturing of High Temperature Alloys)

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Open AccessArticle

Laser Preheating for Hot Crack Reduction in Direct Metal Deposition of Inconel 738LC

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Metals 2022, 12(4), 614; https://doi.org/10.3390/met12040614 - 02 Apr 2022

Cited by 3 | Viewed by 1971

Abstract

Welding of precipitation-hardenable nickel-based super alloys that contain large amounts of Al and Ti is challenging due to their high susceptibility to hot cracking. For metal additive manufacturing (AM) by powder bed fusion (PBF) or direct metal deposition (DMD), various welding process adjustments may prevent the formation of cracks. The aim of this study is the development and experimental characterization of a laser preheating process for DMD of Inconel 738LC. Metallographic cross-sections of multiple test specimens were analyzed to quantify the effect of initial substrate temperature, specimen geometry, deposition parameters, and scanning strategy on the resulting crack density. The results show that increased substrate temperature by laser preheating and reduced specimen size leads to crack-free deposited structures. Therefore, the proposed preheating process may be applied for part fabrication or repair by DMD to reduce or even completely prevent the risk of hot cracking. Full article

(This article belongs to the Special Issue Additive Manufacturing of High Temperature Alloys)

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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Hydrogen embrittlement resistance of additively manufactured 316L stainless steel from recycled sources
Authors: M. Vanazzi1; L.E. Mondora1,2; G. Acquistapace2; N. Mohandas3; M. Scurria4; M. Giovanardi4; Y. Wilkens5; T. Brune5; V. Popovich3
Affiliation: 1. f3nice Srl, Via G. Uberti 12, 20129 Milano (MI), Italy. 2. Valland SpA, Via Roccoli 252, 23010 Piantedo (SO), Italy. 3. Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands. 4. TEC Eurolab Srl, Viale Europa 40, 41011 Campogalliano (MO), Italy. 5. SMS group GmbH, Ohlerkirchweg 66, 41069 Moenchengladbach, Germany
Abstract: To establish a more sustainable approach towards the production and storage of energy, hydrogen has been proposed as the ultimate candidate. Indeed, thanks to several remarkable properties (i.e., high availability, good energy density, greenness in the production and usage) hydrogen stands as an efficient energy source as well as an energy vector. Due to the very demanding operative conditions, however, new material solutions are required to reach a significant deployment of hydrogen-based technologies. In this framework, Additive Manufacturing (AM) or 3D printing has been considered. AM technologies allow the manufacturing of innovative materials with unusual properties, because of the peculiar process-induced microstructure. In the case of metallic materials, superior mechanical properties can be sometimes achieved. In this work, the 316L stainless steel produced by Laser-based Powder Bed Fusion (LB-PBF) has been characterized for hydrogen-related applications. Specimens have been manufactured from 100% recycled material, according to a proprietary process by f3nice. As-printed samples have been pre-charged with gaseous hydrogen at 100 bar pressure and 300 °C, from 5 to 18 days, and subsequently analyzed to check the hydrogen content inside the material. Afterwards, tensile and high-cycles fatigue tests have been performed to investigate the hydrogen-induced degradation mechanisms of the pre-charged material. The resulting properties have been compared to the asprinted counterpart, showing the high-level of compatibility of LB-PBF 316L stainless steel in hydrogen gas. Concerning the tensile tests, no embrittlement was observed. The yield strength does not change after the hydrogen exposure (from 464 ± 3 MPa to 472 ± 5 MPa), while the elongation to rupture remains in the acceptance range (i.e., well above 30%). The fatigue tests present similar outcome. The number of cycles to failure moves from 389.000 ± 107.000 to 477.000 ± 127.000. To conclude, in the present study a highly sustainable hydrogen-resistant 316L stainless steel was printed. The 100% recycled metal has been successfully characterized for hydrogen-related applications, showing good resistance towards hydrogen embrittlement phenomena. These promising results represent a major step forward towards the adoption of metal additive manufacturing from recycled material in relevant industry fields.

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