Editorial

3 pages, 153 KiB

Open AccessEditorial

Ni- and Co-Based Superalloys and their Coatings

by Jonathan Cormier

Metals 2018, 8(12), 1055; https://doi.org/10.3390/met8121055 - 12 Dec 2018

Cited by 2 | Viewed by 2266

Nickel- and Cobalt-based superalloys are state-of-the art materials for the manufacturing of components in the hottest sections of aero-engines and land-based power generation gas turbines. [...] Full article

(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)

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3668 KiB

Open AccessArticle

Experimental and Numerical Modeling of the Stress Rupture Behavior of Nickel-Based Single Crystal Superalloys Subject to Multi-Row Film Cooling Holes

by Yuanming Xu, Weikang Sun, Wei Dai, Chunyan Hu, Xinling Liu and Weifang Zhang

Metals 2017, 7(9), 340; https://doi.org/10.3390/met7090340 - 01 Sep 2017

Cited by 12 | Viewed by 4198

Abstract

The stress rupture behavior of nickel-base single crystal superalloys is a primary issue facing aero-engine design, which has been studied for more than 40 years. To a large degree, it is the existence of film cooling holes with the introduction of air cooling [...] Read more.

The stress rupture behavior of nickel-base single crystal superalloys is a primary issue facing aero-engine design, which has been studied for more than 40 years. To a large degree, it is the existence of film cooling holes with the introduction of air cooling techniques that adds the extra challenge to the problem. Using both experimental and numerical methods, we explore here the stress rupture behavior of nickel base single crystal plate specimens subject to multi-row film cooling holes. As the numerical simulation part, finite element analysis using Abaqus was performed. Numerical results reveal that the existence of film-holes causes stress concentration and transforms local stress from uniaxial to multi-axial. For the stress distribution of different types of specimens, we defined a stress multiaxiality factor to quantitatively characterize the degree of the stress complexity and examined its effect on the rupture behaviors of the specimens along with the true stress concentration factor. The test was also carried out and results indicated that the creep rupture lives of one- and two-row specimens turn out to be longer than those of non-hole specimen. However, the three- and four-row configuration showed the opposite trend. Among the geometric parameters of film-hole configuration, film-hole row spacing is a predominant one influencing the creep rupture properties. Numerical results agree well with the fracture positions and shapes of specimens. Full article

(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)

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4733 KiB

Open AccessArticle

The Effect of Nb/Ti Ratio on Hardness in High-Strength Ni-Based Superalloys

by Hiromu Hisazawa, Yoshihiro Terada, Fauzan Adziman, David J. Crudden, David M. Collins, David E.J. Armstrong and Roger C. Reed

Metals 2017, 7(3), 71; https://doi.org/10.3390/met7030071 - 23 Feb 2017

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Abstract

The age-hardening behaviour and microstructure development of high strength Ni-based superalloys ABD-D2, D4, and D6 with varying Nb/Ti ratios have been studied. The studied alloys have large volume fractions and multimodal size distributions of the γ′ precipitates, making them sensitive to cooling conditions [...] Read more.

The age-hardening behaviour and microstructure development of high strength Ni-based superalloys ABD-D2, D4, and D6 with varying Nb/Ti ratios have been studied. The studied alloys have large volume fractions and multimodal size distributions of the γ′ precipitates, making them sensitive to cooling conditions following solution heat treatment. Differential scanning calorimetry was conducted with a thermal cycle that replicated a processing heat treatment. The hardness of these alloys was subsequently evaluated by nanoindentation. The Nb/Ti ratio was not observed to influence the size and distribution of primary and secondary γ′ precipitates; however, the difference in those of tertiary γ′ and precipitate morphology were observed. The nanoindentation hardness for all alloys reduces once they have been solution-heat-treated. The alloys exhibited specific peak hardness. The alloy with the greatest Nb content was found to have the best increase in hardness among the alloys studied due to its large tertiary γ′ precipitate. Full article

(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)

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2638 KiB

Open AccessArticle

Sputtering Power Effects on Growth and Mechanical Properties of Cr₂AlC MAX Phase Coatings

by Muhammad Naveed, Aleksei Obrosov, Andrzej Zak, Wlodzimierz Dudzinski, Alex A. Volinsky and Sabine Weiß

Metals 2016, 6(11), 265; https://doi.org/10.3390/met6110265 - 05 Nov 2016

Cited by 25 | Viewed by 6294

Abstract

Coating growth and mechanical properties of nanolamellar Cr₂AlC coatings at various sputtering power were investigated in the present study. Cr₂AlC coating was deposited on the IN 718 superalloy and (100) Si wafers by DC magnetron sputtering at different sputtering [...] Read more.

Coating growth and mechanical properties of nanolamellar Cr₂AlC coatings at various sputtering power were investigated in the present study. Cr₂AlC coating was deposited on the IN 718 superalloy and (100) Si wafers by DC magnetron sputtering at different sputtering powers. The structure and properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nanoindentation. It was found that coatings had columnar structure with nanocrystalline substructure. Deposition rate increased with the sputtering power. XRD results showed the presence of the Cr₂AlC MAX phase, intermetallic AlCr₂ and Cr₇C₃ carbide phases, along with the change in preferential coating growth orientation. TEM observations confirmed the occurrence of these phases, and the SAED patterns demonstrated significant texture of the coatings. Hardness values were measured in the range between 11–14 GPa, showing a slight increase with the sputtering power. Full article

(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)

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6662 KiB

Open AccessFeature PaperArticle

Transmission Electron Microscopy of a CMSX-4 Ni-Base Superalloy Produced by Selective Electron Beam Melting

by Alireza B. Parsa, Markus Ramsperger, Aleksander Kostka, Christoph Somsen, Carolin Körner and Gunther Eggeler

Metals 2016, 6(11), 258; https://doi.org/10.3390/met6110258 - 28 Oct 2016

Cited by 23 | Viewed by 7021

Abstract

In this work, the microstructures of superalloy specimens produced using selective electron beam melting additive manufacturing were characterized. The materials were produced using a CMSX-4 powder. Two selective electron beam melting processing strategies, which result in higher and lower effective cooling rates, are [...] Read more.

In this work, the microstructures of superalloy specimens produced using selective electron beam melting additive manufacturing were characterized. The materials were produced using a CMSX-4 powder. Two selective electron beam melting processing strategies, which result in higher and lower effective cooling rates, are described. Orientation imaging microscopy, scanning transmission electron microscopy and conventional high resolution transmission electron microscopy are used to investigate the microstructures. Our results suggest that selective electron beam melting processing results in near equilibrium microstructures, as far as γ′ volume fractions, the formation of small amounts of TCP phases and the partitioning behavior of the alloy elements are concerned. As expected, higher cooling rates result in smaller dendrite spacings, which are two orders of magnitude smaller than observed during conventional single crystal casting. During processing, columnar grains grow in <100> directions, which are rotated with respect to each other. There are coarse γ/γ′ microstructures in high angle boundary regions. Dislocation networks form low angle boundaries. A striking feature of the as processed selective electron beam melting specimens is their high dislocation density. From a fundamental point of view, this opens new possibilities for the investigation of elementary dislocation processes which accompany solidification. Full article

(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)

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3117 KiB

Open AccessArticle

Effects of the Hot Isostatic Pressing Process on Crack Healing of the Laser Repair-Welded CM247LC Superalloy

by Keng-Tu Hsu, Huei-Sen Wang, Hou-Guang Chen and Po-Chun Chen

Metals 2016, 6(10), 238; https://doi.org/10.3390/met6100238 - 10 Oct 2016

Cited by 17 | Viewed by 7124

Abstract

This study investigated the effects of the hot isostatic pressing process on the crack healing, microstructure, and mechanical properties of the laser repair-welded CM247LC precipitation-hardened superalloy. To ensure the strength of the repair-welded area, this study used the direct re-melting approach, and simulated [...] Read more.

This study investigated the effects of the hot isostatic pressing process on the crack healing, microstructure, and mechanical properties of the laser repair-welded CM247LC precipitation-hardened superalloy. To ensure the strength of the repair-welded area, this study used the direct re-melting approach, and simulated the repair welding with the filler addition, which has a chemical composition matching that of the base superalloy. As expected, different types of cracks, including the solidification crack in the weld fusion zone and various types of liquidation cracks in the heat-affected zone, were observed. Through a proper hot isostatic pressing healing process, all cracks in the weld fusion zone and the heat-affected zone of the repair-welded pieces were healed. At the same time, some nano- and micro-sized carbides tended to form discontinuously along the healed crack trace. A micro-hardness test was conducted in the repair-welded area, and the results were similar to that of the as-cast material. Full article

(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)

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6798 KiB

Open AccessArticle

Constitutive Model Based on Dynamic Recrystallization Behavior during Thermal Deformation of a Nickel-Based Superalloy

by Peng Zhang, Cen Yi, Gang Chen, Heyong Qin and Chuanjie Wang

Metals 2016, 6(7), 161; https://doi.org/10.3390/met6070161 - 13 Jul 2016

Cited by 46 | Viewed by 6515

Abstract

The thermal deformation and dynamic recrystallization (DRX) behavior of a nickel-based superalloy were investigated by the thermal compression test. The experimental results show that the process parameters have great influence on the flow stress of the superalloy. In addition, there is an inflection [...] Read more.

The thermal deformation and dynamic recrystallization (DRX) behavior of a nickel-based superalloy were investigated by the thermal compression test. The experimental results show that the process parameters have great influence on the flow stress of the superalloy. In addition, there is an inflection point on the DRX softening stage of the work-hardening rate versus stress curve. DRX under the conditions of higher temperatures and lower strain rates easily occurs when the strain reaches a critical level. Based on the classical dislocation density theory and the DRX kinetics models, a two-stage constitutive model considering the effect of work hardening-dynamic recovery and DRX is developed for the superalloy. Comparisons between the predicted and experimental data indicate that the values predicted by the proposed constitutive model are in good agreement with the experimental results. Full article

(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)

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Graphical abstract

5481 KiB

Open AccessFeature PaperArticle

Contact Properties and Wear Behaviour of Nickel Based Superalloy René 80

by Mario Lavella

Metals 2016, 6(7), 159; https://doi.org/10.3390/met6070159 - 12 Jul 2016

Cited by 30 | Viewed by 6459

Abstract

A superalloy traditionally offers excellent mechanical strength, resistance to thermal creep deformation, good surface stability and resistance to corrosion or oxidation. However, a superalloy often also needs performance in terms of fretting resistance. Experimental results regarding fretting wear and contact properties of the [...] Read more.

A superalloy traditionally offers excellent mechanical strength, resistance to thermal creep deformation, good surface stability and resistance to corrosion or oxidation. However, a superalloy often also needs performance in terms of fretting resistance. Experimental results regarding fretting wear and contact properties of the superalloy René 80 are illustrated and discussed. The widespread applications of superalloys in jointing with friction as in the jointing of a turbine blade, is the main motivation for characterizing their fretting behaviour. The fretting experiments were performed at 100 Hz for two temperatures (600, 800 °C), and two sliding amplitudes (30, 60 µm). These temperatures and strokes are typical at the medium stage of a low-pressure gas turbine. Wear volume and the contact properties such as friction coefficient and tangential contact stiffness were measured and analysed. Results show that the lowest friction coefficient was measured at the temperature of 800 °C. This temperature hence appears to be an optimum working condition for the fretting wear of René 80. With regard to wear mechanism, a fundamental role of the sliding amplitude was found. In particular, the ratio between the sliding amplitude and the characteristic contact length has a significant influence upon the oxide growth on contact surfaces. Full article

(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)

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