Single-Crystal Ni-Based Alloys

Topic Information

Dear Colleagues,

Single-crystal alloys are the biggest technological advancement since the emergence of high-temperature superalloys in 1940s, with a number of applications in, among others, aerospace and power generation. The manufacturing process is carefully carried out to control the thermal gradient and remove the grain boundary so as to produce a single crystalline form. This leads to excellent mechanical performance (long creep and fatigue life) and resistance to chemical degradation (oxidation and corrosion), especially at high temperatures close to their melting points. However, the manufacture of single-crystal nickel-based alloys via investment casting can introduce some unexpected, undesirable grain boundaries or other metallurgical defects which break the single-crystal form and enormously degrade the mechanical performance under high-temperature and high-pressure operating conditions. To mitigate those defects, the manufacture processing conditions should be precisely controlled using both computational and experimental approaches. Consequently, understanding the compositional–metallurgical process is of great importance to prevent and ultimately eliminate the defects of single-crystal alloys. We would like to invite academics and researchers to contribute to this Special Issue on “Single-Crystal Ni-Based Alloys”, which is intended to serve as a unique multidisciplinary forum covering broad aspects of science, technology, and the application of single crystal Ni-based alloys. The potential topics include but are not limited to:

• Materials design of single-crystal Ni-based alloys;
• Processing and process modelling of single-crystal Ni-based alloys;
• Integrated computational materials engineering (ICME)/high-fidelity modelling;
• Solidification and defect control of single-crystal Ni-based alloys; 
• Materials characterisation of single-crystal Ni-based alloys using advanced techniques; 
• Physical metallurgy of single-crystal Ni-based alloys.

Prof. Dr. Hongbiao Dong
Dr. Chinnapat Panwisawas
Prof. Dr. Paul A. Withey
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Crystals crystals	2.4	4.2	2011	11.1 Days	CHF 2100
Metals metals	2.6	4.9	2011	17.8 Days	CHF 2600

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Published Papers (9 papers)

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16 pages, 4686 KiB  

Open AccessFeature PaperArticle

A Sharp-Interface Model of the Diffusive Phase Transformation in a Nickel-Based Superalloy

by Lukas Munk, Silvia Reschka, Hans Jürgen Maier, Peter Wriggers and Stefan Löhnert

Metals 2022, 12(8), 1261; https://doi.org/10.3390/met12081261 - 27 Jul 2022

Cited by 2 | Viewed by 1855

Abstract

A sharp-interface model employing the extended finite element method is presented. It is designed to capture the prominent $\gamma$-${\gamma }^{\prime }$ phase transformation in nickel-based superalloys. The novel combination of crystal plasticity and sharp-interface theory outlines a good modeling alternative to approaches [...] Read more.

A sharp-interface model employing the extended finite element method is presented. It is designed to capture the prominent $\gamma$-${\gamma }^{\prime }$ phase transformation in nickel-based superalloys. The novel combination of crystal plasticity and sharp-interface theory outlines a good modeling alternative to approaches based on the Cahn–Hilliard equation. The transformation is driven by diffusion of solute ${\gamma }^{\prime }$-forming elements in the $\gamma$-phase. Boundary conditions for the diffusion problem are computed by the stress-modified Gibbs–Thomson equation. The normal mass balance of solute atoms at the interface yields the normal interface velocity, which is integrated in time by a level set procedure. In order to capture the influence of dislocation glide and climb on interface motion, a crystal plasticity model is assumed to describe the constitutive behaviour of the $\gamma$-phase. Cuboidal equilibrium shapes and Ostwald ripening can be reproduced. According to the model, in low ${\gamma }^{\prime }$ volume-fraction alloys with separated ${\gamma }^{\prime }$-precipitates, interface movement does not have a significant effect on tensile creep behaviour at various lattice orientations. Full article

(This article belongs to the Topic Single-Crystal Ni-Based Alloys)

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12 pages, 3582 KiB  

Open AccessArticle

Temperature Field Evolution of Seeding during Directional Solidification of Single-Crystal Ni-Based Superalloy Castings

by Songsong Hu, Yunsong Zhao, Weimin Bai, Xinming Wang, Fucheng Yin, Wenchao Yang and Lin Liu

Metals 2022, 12(5), 817; https://doi.org/10.3390/met12050817 - 9 May 2022

Cited by 3 | Viewed by 2534

Abstract

By combined numerical simulations and unidirectional solidification experiments, the temperature field evolution of seeding for nickel-based single-crystal superalloys was studied. At the steady state, the position of the mushy zone in the seed moves down as the melt is poured into the mold. [...] Read more.

By combined numerical simulations and unidirectional solidification experiments, the temperature field evolution of seeding for nickel-based single-crystal superalloys was studied. At the steady state, the position of the mushy zone in the seed moves down as the melt is poured into the mold. The holding time required for the temperature field of the seed segment to reach the steady state is less for seeds with casting than for those without casting. The holding time required to completely eliminate randomly oriented broken dendrites in the melt-back zone is much longer than that required for the temperature field to achieve a steady state. A short incubation stage is required before the temperature field evolution process; then, the migration rate of the isotherm gradually increases until it is the vicinity of the withdrawal rate. Finally, the effect of temperature field evolution on the formation of stray grains in seed segments is discussed. Full article

(This article belongs to the Topic Single-Crystal Ni-Based Alloys)

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11 pages, 3076 KiB  

Open AccessEditor’s ChoiceArticle

Compositions of Gamma and Gamma Prime Phases in an As-Cast Nickel-Based Single Crystal Superalloy Turbine Blade

by KeeHyun Park and Paul Withey

Crystals 2022, 12(2), 299; https://doi.org/10.3390/cryst12020299 - 20 Feb 2022

Cited by 8 | Viewed by 5962

Abstract

The core and the interdendritic regions of an as-cast nickel based single crystal turbine blade were observed by electron microscopy to understand the microstructural development during an investment casting process. The dendrite core region shows an irregular morphology of gamma prime in gamma [...] Read more.

The core and the interdendritic regions of an as-cast nickel based single crystal turbine blade were observed by electron microscopy to understand the microstructural development during an investment casting process. The dendrite core region shows an irregular morphology of gamma prime in gamma due to a relatively short casting time, which prevented the development of gamma prime expected in a solution heat-treated microstructure. By comparison, the interdendritic region comprises three different regions composed of: several elongated gamma prime particles, relatively tiny and irregular gamma prime, and gamma prime with relatively regular morphology. The chemical analysis of these phases showed that, regardless of the analysis point in the core or the interdendritic region, almost the same compositions were acquired in the regular type of gamma and gamma prime phases. This result suggests that if the gamma prime forms in the gamma matrix, the composition of gamma prime is almost uniform regardless of the region and prevailing general chemical composition. In contrast, the composition of the elongated gamma prime in the interdendritic region was slightly different depending on the analysis point even within the same elongated particle. Full article

(This article belongs to the Topic Single-Crystal Ni-Based Alloys)

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12 pages, 65124 KiB  

Open AccessArticle

Modeling of the Effect of Secondary Orientation on the Micro Deformation Behavior of Ni-Based Single Crystal Superalloys

by Wencong Wei, Jinxia Song, Jiawei Zhang, Shijin Nie, Lin Li, Chengbo Xiao and Furong Liu

Metals 2022, 12(2), 217; https://doi.org/10.3390/met12020217 - 24 Jan 2022

Viewed by 2487

Abstract

In this paper, a supercell modeling of secondary orientation was established using 90 cubic mosaic units made up of γ’ phase embedded in γ matrix, in accordance with an actual structure of Ni-based single crystal superalloys (NSCS). The effects of secondary orientation on [...] Read more.

In this paper, a supercell modeling of secondary orientation was established using 90 cubic mosaic units made up of γ’ phase embedded in γ matrix, in accordance with an actual structure of Ni-based single crystal superalloys (NSCS). The effects of secondary orientation on the deformation behavior and microstructure evolution of NSCS under uniaxial tensile were studied by a three-dimensional molecular dynamics (MD) simulation. Simulation results showed that secondary orientation had a significant effect on mechanical properties of NSCS, that is, a big fluctuation was found in tensile strength which dropped down almost 50% from a peak (corresponding to the secondary orientations of 18° and 45°) to a trough (those of 34° and 63°). Mechanisms of secondary orientation affecting the deformation behavior were further discussed systematically. The deformation of NSCS under uniaxial tensile was a process tending towards amorphization of microstructure, together with the dislocation formation, merging and break-up. On a micro viewpoint, this work for us will be useful to apprehend the tensile deformation conduct of NSCS. Full article

(This article belongs to the Topic Single-Crystal Ni-Based Alloys)

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15 pages, 30288 KiB  

Open AccessEditor’s ChoiceArticle

Influence of Cooling Scenarios on the Evolution of Microstructures in Nickel-Based Single Crystal Superalloys

by Zhengxing Feng, Zhixun Wen, Guangxian Lu and Yanchao Zhao

Crystals 2022, 12(1), 74; https://doi.org/10.3390/cryst12010074 - 6 Jan 2022

Cited by 6 | Viewed by 2348

Abstract

The reprecipitation and evolution of γ’ precipitates during various cooling approaches from supersolvus temperature are studied experimentally and via phase field simulation in nickel-based single crystal superalloys. The focus of this paper is to explore the influence of cooling methods on the evolution [...] Read more.

The reprecipitation and evolution of γ’ precipitates during various cooling approaches from supersolvus temperature are studied experimentally and via phase field simulation in nickel-based single crystal superalloys. The focus of this paper is to explore the influence of cooling methods on the evolution of the morphology and the distribution of γ’ precipitates. It is demonstrated that small and uniform spherical shape γ’ particles formed with air cooling method. When the average cooling rate decreases, the particle number decreases while the average matrix and precipitate channel widths increase. The shape of γ’ precipitates which changed from spherical to cubic and irregular characteristics due to the elastic interaction and elements diffusion are observed with the decrease of the average cooling rate. The phase field simulation results are in good agreement with the experimental results in this paper. The research is a benefit for the study of the rejuvenation heat treatment in re-service nickel-based superalloys. Full article

(This article belongs to the Topic Single-Crystal Ni-Based Alloys)

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12 pages, 6464 KiB  

Open AccessArticle

Study on the Evolution of the γ′ Phase and Grain Boundaries in Nickel-Based Superalloy during Interrupted Continuous Cooling

by Haiping Wang, Dong Liu, Jianguo Wang, Yanhui Yang, Haodong Rao, Hai Wang, Jungang Nan and Longxiang Wang

Crystals 2021, 11(12), 1464; https://doi.org/10.3390/cryst11121464 - 26 Nov 2021

Cited by 6 | Viewed by 2358

Abstract

The formation of the irregular γ′ precipitates in the nickel-based superalloy Waspaloy was investigated during the continuous cooling, which is relevant to the cooling rates and interrupted temperature. The morphology of the γ′ precipitates was observed to change from a dispersed sphere to [...] Read more.

The formation of the irregular γ′ precipitates in the nickel-based superalloy Waspaloy was investigated during the continuous cooling, which is relevant to the cooling rates and interrupted temperature. The morphology of the γ′ precipitates was observed to change from a dispersed sphere to the flower-like one with the decreasing of the cooling rates. It was found that there are three modes of transportation of the solute atoms involved in relation to the γ′ precipitates: dissolution from the small γ′ precipitates to the γ matrix, diffusion to the large γ′ precipitates from the matrix, and the short distance among γ′ precipitates close to each other. Meanwhile, the slower cooling rates tend to result in the serrated grain boundaries, and the wavelength between successive peaks (λ) and the maximum amplitude (A) are larger with the decreasing of the cooling rates. The content of the low ΣCSL boundaries increases with the decreasing of the cooling rates, which is of great benefit in improving the creep property of the Waspaloy. Full article

(This article belongs to the Topic Single-Crystal Ni-Based Alloys)

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13 pages, 10142 KiB  

Open AccessArticle

Quantitative Characterization of the γ’ Phase Distribution in the Large-Scale Area of the Second-Generation Nickel-Based Single Crystal Blade DD5

by Weihao Wan, Dongling Li, Qingqing Zhou, Qiang Zeng, Xin Xue, Hui Shi and Haizhou Wang

Crystals 2021, 11(11), 1399; https://doi.org/10.3390/cryst11111399 - 17 Nov 2021

Cited by 3 | Viewed by 2035

Abstract

Nickel-based single crystal superalloy blades have excellent high-temperature performance as the hot end part of the aero-engine turbine. The most important strengthening phase in the single crystal blade is the γ’ phase, and its morphology and size distribution directly affect the high [...] Read more.

Nickel-based single crystal superalloy blades have excellent high-temperature performance as the hot end part of the aero-engine turbine. The most important strengthening phase in the single crystal blade is the γ’ phase, and its morphology and size distribution directly affect the high temperature performance of the single crystal blade. In this work, scanning electron microscopy (SEM) was used to obtain the microscopic images of the γ’ phase in multiple large continuous fields of view in the transverse sections of single crystal blades, and the quantitative statistical characterization of the γ’ phase was performed by image segmentation method based on deep learning. The 20 μm × 20 μm region was selected from the primary dendrite arm, the secondary dendrite arm, and the interdendrite to statistically analyze the γ’ phases. The statistical results show that the average size of the γ’ phase at the position of the interdendrite is significantly larger than the average size of the γ’ phase at the position of the dendrite; the sizes of the γ’ phase at the primary dendrite arm, the secondary dendrite arm and the interdendrite all obey the normal distribution; about 3.17 × 10⁷ γ’ phases are counted in 20 positions in the 5 transverse sections of the single crystal blade in a total area of 5 mm², and the size, geometric morphology and area fraction of all γ’ phases are respectively counted. In this work, the quantitative parameters of the γ’ phases at 4 different positions of the section of the single crystal superalloy DD5 blade were compared, the size and area fraction of the γ’ phases at the leading edge and the trailing edge were smaller, and the shape of the γ’ phase of the leading edge and the trailing edge is closer to the cube. Full article

(This article belongs to the Topic Single-Crystal Ni-Based Alloys)

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16 pages, 10787 KiB  

Open AccessArticle

Hot Deformation Behavior and Processing Map of GH901 Superalloy

by Rui Ma, Lulu Li, Ruixue Zhai, Xiangnan Meng and Jun Zhao

Metals 2021, 11(11), 1808; https://doi.org/10.3390/met11111808 - 10 Nov 2021

Cited by 5 | Viewed by 1844

Abstract

During the forging process GH901 superalloys easily produce cracks and defects, such as coarse crystals in tissues, which affect the performance of the alloy. Using GH901 nickel-based alloy, high-temperature compression tests at deformation temperatures of 990, 1040, 1090 and 1140 °C were carried [...] Read more.

During the forging process GH901 superalloys easily produce cracks and defects, such as coarse crystals in tissues, which affect the performance of the alloy. Using GH901 nickel-based alloy, high-temperature compression tests at deformation temperatures of 990, 1040, 1090 and 1140 °C were carried out in a Thermecmastor-Z thermal simulator, with strain rates 0.001, 0.01, 0.1 and 1 s⁻¹. Next, the isothermal forging process of a GH901 disc was simulated using DEFORM finite element simulation software. The results showed that with the increase in deformation temperatures and the decrease in strain rates, the flow stress clearly decreased. The flow stress constitutive model of GH901 superalloy under ${\epsilon }_{0.3}$ and the flow stress constitutive model for strain compensation were obtained. The processing map was built, and a reasonable range of thermal processing was obtained. Meanwhile, the isothermal forging simulation verified the reliability of the thermal processing range of the alloy. Full article

(This article belongs to the Topic Single-Crystal Ni-Based Alloys)

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17 pages, 6018 KiB  

Open AccessArticle

General View of Rhenium-Rich Particles along Defect Grain Boundaries Formed in Nickel-Based Single-Crystal Superalloy Turbine Blades: Formation, Dissolution and Comparison with Other Phases

by KeeHyun Park and Paul Withey

Crystals 2021, 11(10), 1201; https://doi.org/10.3390/cryst11101201 - 6 Oct 2021

Cited by 7 | Viewed by 2880 | Correction

Abstract

Nickel-based single-crystal superalloy turbine blades have been widely used in engines of aircrafts or power plants, but some defect grains are often found on the surface of the blade after full heat treatment or even after casting. Rhenium-rich particles, as well as an [...] Read more.

Nickel-based single-crystal superalloy turbine blades have been widely used in engines of aircrafts or power plants, but some defect grains are often found on the surface of the blade after full heat treatment or even after casting. Rhenium-rich particles, as well as an intermediate layer, were almost always detected along any defect grain boundary region, if it existed, from a low-angle grain boundary to a high-angle boundary. The particles were also found on the top surface of the base material. The composition and morphology of the particles were different from the most common topologically close packed phases or a fine particle with similar morphology detected at the boundary region between a recrystallized grain and a matrix grain. An additional heat treatment could completely dissolve the fine particles. Furthermore, any rhenium-rich particles were not re-formed after achieving uniform distribution of the alloying elements. Full article

(This article belongs to the Topic Single-Crystal Ni-Based Alloys)

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