Special Issue "Superalloys"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 December 2015)

Special Issue Editor

Guest Editor
Dr. Johan Moverare

Division of Engineering Materials, Department of Management & Engineering, Linköping University, SE-581 83 Linköping, Sweden
E-Mail
Phone: +46 13 281141
Interests: superalloys; thermomechanical fatigue; creep; oxidation; aging; material modelling

Special Issue Information

Dear Colleagues,

Superalloys are Ni- and Co-based high temperature alloys that can be found in many important industrial systems, e.g., for aerospace propulsion, energy generation, and chemical processing. Superalloys have outstanding high temperature strength and oxidation resistance, but are not cheap materials, and must therefore demonstrate value to the customers by some other means, and are therefore most often found in critical components in severe environments operating near the limits of their capability. As a consequence, good knowledge about superalloys is very important, and a lot of scientific works have been dedicated to these materials. Still, there are significant demands for improved high temperature materials to enable further technology advances, and therefore, the scientific and engineering interest for superalloys remains. This Special Issue focuses on advances in alloy development and processing, the characterization and modeling of high temperature behavior, and the physical metallurgy of superalloys.

Dr. Johan Moverare
Guest Editor

Manuscript Submission Information

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Keywords

  • superalloys
  • high temperature
  • ni-based alloys
  • co-based alloys
  • single crystals
  • creep
  • fatigue
  • oxidation

Published Papers (12 papers)

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Research

Open AccessArticle Investigation on Hot Deformation Behavior and Hot Processing Map of BSTMUF601 Super-Alloy
Metals 2016, 6(3), 70; doi:10.3390/met6030070
Received: 23 January 2016 / Revised: 9 March 2016 / Accepted: 15 March 2016 / Published: 19 March 2016
Cited by 2 | PDF Full-text (2308 KB) | HTML Full-text | XML Full-text
Abstract
Isothermal compression tests of BSTMUF601 super-alloy in the temperature range of 950 °C–1200 °C and at the strain rates of 0.2 s−1, 5 s−1, 10 s−1 were performed on a Gleeble-1500D thermo-mechanical simulator. Based on the hyperbolic sine
[...] Read more.
Isothermal compression tests of BSTMUF601 super-alloy in the temperature range of 950 °C–1200 °C and at the strain rates of 0.2 s−1, 5 s−1, 10 s−1 were performed on a Gleeble-1500D thermo-mechanical simulator. Based on the hyperbolic sine function, the unified constitutive equations and hot processing maps during the hot deformation process were established. The flow stress predicted by the constitutive equations shows good agreement with the corrected stress. Hot processing maps for hot working conditions were established based on exploring the effect of power dissipation efficiency and the instability coefficient associated with various kinds of temperatures and stain rates. Subsequently, power dissipation efficiency and the instability coefficient were interpreted based on hot processing maps under a series of strains, temperatures and strain rates. The results show that power dissipation efficiency increases gradually with the increasing temperature and the decreasing stain rate, and instability domains reduce first, then increase with the increase of true strain. The optimum hot working condition of BSTMUF601 super-alloy was obtained. Full article
(This article belongs to the Special Issue Superalloys)
Open AccessArticle Research on the Grain Boundary Liquation Mechanism in Heat Affected Zones of Laser Forming Repaired K465 Nickel-Based Superalloy
Metals 2016, 6(3), 64; doi:10.3390/met6030064
Received: 27 January 2016 / Revised: 24 February 2016 / Accepted: 29 February 2016 / Published: 15 March 2016
Cited by 1 | PDF Full-text (3311 KB) | HTML Full-text | XML Full-text
Abstract
The damaged K465 nickel-based superalloy parts were repaired by laser forming repair technology. The cracking characteristics and grain boundary liquation in heat affected zones were investigated by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that
[...] Read more.
The damaged K465 nickel-based superalloy parts were repaired by laser forming repair technology. The cracking characteristics and grain boundary liquation in heat affected zones were investigated by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that the cracks originated from the heat-affected zone and extended to the repaired zone. The calculation by Thermol-Cale software showed that the larger γ′ particles at grain boundaries partly dissolved in the γ phase, which made the solutes’ concentration at the γ′/γ interface meet the eutectic-type liquation reaction condition of γ + γ′ → L. Then, grain boundaries liquation occurred and liquid films appeared with the temperature increasing in a rapid heating process. However, the intragranular γ′ phase completely dissolved into the γ phase with no devotion to the liquid film. The dissolution of M5B3 borides at grain boundaries could promote grain boundary liquation. Full article
(This article belongs to the Special Issue Superalloys)
Open AccessArticle Characterisation of an Advanced Nickel Based Superalloy Post Cold Work by Swaging
Metals 2016, 6(3), 54; doi:10.3390/met6030054
Received: 21 December 2015 / Revised: 27 January 2016 / Accepted: 23 February 2016 / Published: 4 March 2016
Cited by 1 | PDF Full-text (9176 KB) | HTML Full-text | XML Full-text
Abstract
Cylindrical bars of the advanced nickel based superalloy RR1000 were subjected to swaging to induce approximately 30% cold work. Grain size analysis demonstrated a distinct modification to the microstructure whilst electron back scattered diffraction (EBSD) measurements confirmed the evolution of a relatively strong
[...] Read more.
Cylindrical bars of the advanced nickel based superalloy RR1000 were subjected to swaging to induce approximately 30% cold work. Grain size analysis demonstrated a distinct modification to the microstructure whilst electron back scattered diffraction (EBSD) measurements confirmed the evolution of a relatively strong <111> texture parallel with the longitudinal bar axis. Intragranular strain damage was identified. The effects of the swaging on bulk mechanical properties are illustrated across a range of test temperatures. Full article
(This article belongs to the Special Issue Superalloys)
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Open AccessArticle Formation and Dissolution of γ’ Precipitates in IN792 Superalloy at Elevated Temperatures
Metals 2016, 6(2), 37; doi:10.3390/met6020037
Received: 4 December 2015 / Revised: 22 January 2016 / Accepted: 1 February 2016 / Published: 17 February 2016
Cited by 1 | PDF Full-text (3756 KB) | HTML Full-text | XML Full-text
Abstract
Precipitation of γ’ phase in nickel-base superalloy IN792-5A was studied using in-situ Small Angle Neutron Scattering (SANS). It was found that additional precipitates are formed after reheating above 600 °C when the material is previously fast cooled (100 K/min) from 900 °C. The
[...] Read more.
Precipitation of γ’ phase in nickel-base superalloy IN792-5A was studied using in-situ Small Angle Neutron Scattering (SANS). It was found that additional precipitates are formed after reheating above 600 °C when the material is previously fast cooled (100 K/min) from 900 °C. The size distribution and volume fraction of the additional γ’ precipitates as well as of the already present medium-size precipitates in dependence on temperature were evaluated. The small precipitates can influence mechanical properties of the alloy, which exhibits an anomaly in the temperature dependence of the yield stress. Volume fraction of all precipitate populations above 900 °C was estimated as well. Full article
(This article belongs to the Special Issue Superalloys)
Figures

Open AccessArticle Evolution of the Annealing Twin Density during δ-Supersolvus Grain Growth in the Nickel-Based Superalloy Inconel™ 718
Metals 2016, 6(1), 5; doi:10.3390/met6010005
Received: 1 November 2015 / Revised: 14 December 2015 / Accepted: 17 December 2015 / Published: 24 December 2015
Cited by 3 | PDF Full-text (5422 KB) | HTML Full-text | XML Full-text
Abstract
Grain growth experiments were performed on Inconel™ 718 to investigate the possible correlation of the annealing twin density with grain size and with annealing temperature. Those experiments were conducted at different temperatures in the δ supersolvus domain and under such conditions that only
[...] Read more.
Grain growth experiments were performed on Inconel™ 718 to investigate the possible correlation of the annealing twin density with grain size and with annealing temperature. Those experiments were conducted at different temperatures in the δ supersolvus domain and under such conditions that only capillarity forces were involved in the grain boundary migration process. In the investigated range, there is a strong inverse correlation of the twin density with the average grain size. On the other hand, the twin density at a given average grain size is not sensitive to annealing temperature. Consistent with previous results for pure nickel, the twin density evolution in Inconel™ 718 is likely to be mainly controlled by the propagation of the pre-existing twins of the growing grains; i.e., the largest ones of the initial microstructure. Almost no new twin boundaries are created during the grain growth process itself. Therefore, the twin density at a given average grain size is mainly dependent on the twin density in the largest grains of the initial microstructure and independent of the temperature at which grains grow. Based on the observations, a mean field model is proposed to predict annealing twin density as a function of grain size during grain growth. Full article
(This article belongs to the Special Issue Superalloys)
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Open AccessArticle Effect of Cold Rolling and Heat Treatment on the Mechanical Properties of GH4169 Alloy Sheet at Room Temperature
Metals 2016, 6(1), 1; doi:10.3390/met6010001
Received: 31 October 2015 / Revised: 14 December 2015 / Accepted: 15 December 2015 / Published: 23 December 2015
Cited by 1 | PDF Full-text (3451 KB) | HTML Full-text | XML Full-text
Abstract
The mechanical properties of GH4169 alloy sheet after cold rolling (at 0%, 10%, 30%, 50% and 70%) and solid solution were investigated. The textures and Taylor factors were characterized using electron backscattering diffraction (EBSD). The fractions of δ phase were measured by X-ray
[...] Read more.
The mechanical properties of GH4169 alloy sheet after cold rolling (at 0%, 10%, 30%, 50% and 70%) and solid solution were investigated. The textures and Taylor factors were characterized using electron backscattering diffraction (EBSD). The fractions of δ phase were measured by X-ray diffraction. The contributions of δ phase, grain size, texture, and work hardening on the mechanical properties were also discussed. The results showed increases in the yield strength (YS) (0.2%) as well as the ultimate tensile strength (UTS) of GH4169 superalloy sheet after cold rolling, when rolling reduction was increased. In contrast, following solid solution treatment, YS and UTS were increased then subsequently decreased. The changes of yield strength of GH4169 superalloy were attributed to the texture and work hardening, followed by the grain refinement and precipitation of δ phase. When the rolling reduction was below 30%, the influence of δ phase was greater than grain refinement and when the rolling reduction was larger than 50%, the controversial results occur. The precipitation of δ phase promoted the improvement of yield strength, the relationship between the fraction of δ phase and improved yield strength satisfactory fit to the following equation: σδ = 15.9Wδ + 59.7. Full article
(This article belongs to the Special Issue Superalloys)
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Open AccessArticle Continuous Casting of Incoloy800H Superalloy Billet under an Alternating Electromagnetic Field
Metals 2016, 6(1), 2; doi:10.3390/met6010002
Received: 28 October 2015 / Revised: 10 December 2015 / Accepted: 15 December 2015 / Published: 23 December 2015
PDF Full-text (3850 KB) | HTML Full-text | XML Full-text
Abstract
We experimentally investigate the influence of an alternating electromagnetic field on the surface and internal qualities of Incoloy800H superalloy billets. The electromagnetic continuous casting experiments for Incoloy800H superalloy were successfully conducted and the billets (0.1 m × 0.1 m × 1.2 m) were
[...] Read more.
We experimentally investigate the influence of an alternating electromagnetic field on the surface and internal qualities of Incoloy800H superalloy billets. The electromagnetic continuous casting experiments for Incoloy800H superalloy were successfully conducted and the billets (0.1 m × 0.1 m × 1.2 m) were obtained. We figure out that the high frequency (20.4 kHz) electromagnetic field which is applied in the mould region can improve the surface quality of Incoloy800H superalloy billet remarkably; the depth of oscillation mark decreases from 1.2 mm (without electromagnetic field) to 0.3 mm (with electromagnetic field). The internal quality of the billet was studied using a variety of characterization techniques. The low frequency (5 Hz) electromagnetic field which is applied in the second cooling region can improve the internal quality; the region of the equiaxed grain increases from 2.45% (without electromagnetic field) to 41.45% (with electromagnetic field). Furthermore, macro- and micro-segregation are suppressed and the TiN inclusion number is decreased as well. Full article
(This article belongs to the Special Issue Superalloys)
Figures

Open AccessArticle Hot Ductility Loss in a Fe-Ni-Based Superalloy
Metals 2015, 5(4), 2428-2434; doi:10.3390/met5042428
Received: 31 October 2015 / Revised: 29 November 2015 / Accepted: 15 December 2015 / Published: 21 December 2015
PDF Full-text (538 KB) | HTML Full-text | XML Full-text
Abstract
High temperature tensile tests have been conducted on samples of a Fe-Ni based superalloy, Incoloy A-286, and significant ductility loss has been observed at 1220 °C. Titanium-rich, thin-film-like phase has been found on the inter-granular facets of fracture surfaces. It appears that sulfur
[...] Read more.
High temperature tensile tests have been conducted on samples of a Fe-Ni based superalloy, Incoloy A-286, and significant ductility loss has been observed at 1220 °C. Titanium-rich, thin-film-like phase has been found on the inter-granular facets of fracture surfaces. It appears that sulfur content of Ti-rich phase was higher than that of the matrix. At 1220 °C, liquation of Ti-rich phases has resulted in thin-film-like morphology along the grain boundary and caused the ductility loss during tensile deformation. Full article
(This article belongs to the Special Issue Superalloys)
Figures

Open AccessFeature PaperArticle Relationships between Microstructural Parameters and Time-Dependent Mechanical Properties of a New Nickel-Based Superalloy AD730™
Metals 2015, 5(4), 2236-2251; doi:10.3390/met5042236
Received: 5 November 2015 / Revised: 20 November 2015 / Accepted: 23 November 2015 / Published: 27 November 2015
Cited by 4 | PDF Full-text (1773 KB) | HTML Full-text | XML Full-text
Abstract
High temperature creep and dwell-fatigue properties of the new nickel-based superalloy AD730™ have been investigated. Three microstructures have been studied in creep (850 °C and 700 °C) and dwell-fatigue (700 °C stress control with trapezoidal signals, and dwell times ranging from 1 s
[...] Read more.
High temperature creep and dwell-fatigue properties of the new nickel-based superalloy AD730™ have been investigated. Three microstructures have been studied in creep (850 °C and 700 °C) and dwell-fatigue (700 °C stress control with trapezoidal signals, and dwell times ranging from 1 s to 3600 s): a coarse grains microstructure, a fine grains one, and single crystalline samples. The aim of this study is to assess the influence of the grain size on creep and creep-fatigue properties. It is demonstrated that fine and coarse grains microstructures perform similarly in creep at 700 °C, showing that the creep properties at this temperature are controlled by the intragranular precipitation. Moreover, both the coarse grains and the fine grains microstructures show changes in creep deformation mechanisms depending on the applied stress in creep at 700 °C. At higher creep temperatures, the coarse grains microstructure performs better and almost no effect is observed by suppressing grain boundaries. During dwell-fatigue tests at 700 °C, a clear effect of the mechanical cycling has been evidenced on the time to failure on both the coarse and the fine grains microstructures. At high applied stresses, a beneficial effect of the cyclic unloading to the lifetime has been observed whereas at lower applied stresses, mechanical cycling is detrimental compared to the pure creep lifetime due to the development of a fatigue damage. Complex creep-fatigue interactions are hence clearly evidenced and they depend on the pure creep behavior reference. Full article
(This article belongs to the Special Issue Superalloys)
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Open AccessArticle Cyclic Oxidation of High Mo, Reduced Density Superalloys
Metals 2015, 5(4), 2165-2185; doi:10.3390/met5042165
Received: 31 October 2015 / Revised: 13 November 2015 / Accepted: 18 November 2015 / Published: 24 November 2015
Cited by 2 | PDF Full-text (1496 KB) | HTML Full-text | XML Full-text
Abstract
Cyclic oxidation was characterized as part of a statistically designed, 12-alloy compositional study of 2nd generation single crystal superalloys as part of a broader study to co-optimize density, creep strength, and cyclic oxidation. The primary modification was a replacement of 5 wt. %
[...] Read more.
Cyclic oxidation was characterized as part of a statistically designed, 12-alloy compositional study of 2nd generation single crystal superalloys as part of a broader study to co-optimize density, creep strength, and cyclic oxidation. The primary modification was a replacement of 5 wt. % W by 7% or 12% Mo for density reductions of 2%–7%. Compositions at two levels of Mo, Cr, Co, and Re were produced, along with a midpoint composition. Initially, polycrystalline vacuum induction samples were screened in 1100 °C cyclic furnace tests using 1 h cycles for 200 h. The behavior was primarily delimited by Cr content, producing final weight changes of −40 mg/cm2 to −10 mg/cm2 for 0% Cr alloys and −2 mg/cm2 to +1 mg/cm2 for 5% Cr alloys. Accordingly, a multiple linear regression fit yielded an equation showing a strong positive Cr effect and lesser negative effects of Co and Mo. The results for 5% Cr alloys compare well to −1 mg/cm2, and +0.5 mg/cm2 for Rene′ N4 and Rene′ N5 (or Rene′ N6), respectively. Scale phases commonly identified were Al2O3, NiAl2O4, NiTa2O6, and NiO, with (Ni,Co)MoO4 found only on the least resistant alloys having 0% Cr and 12% Mo. Scale microstructures were complex and reflected variations in the regional spallation history. Large faceted NiO grains and fine NiTa2O6 particles distributed along NiAl2O4 grain boundaries were typical distinctive features. NiMoO4 formation, decomposition, and volatility occurred for a few high Mo compositions. A creep, density, phase stability, and oxidation balanced 5% Cr, 10% Co, 7% Mo, and 3% Re alloy was selected to be taken forward for more extensive evaluations in single crystal form. Full article
(This article belongs to the Special Issue Superalloys)
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Open AccessArticle Investigation of the Undercoolability of Ni-Based Alloys Using High Temperature Thermal Analysis
Metals 2015, 5(4), 1971-1983; doi:10.3390/met5041971
Received: 21 August 2015 / Revised: 16 October 2015 / Accepted: 20 October 2015 / Published: 26 October 2015
Cited by 1 | PDF Full-text (1157 KB) | HTML Full-text | XML Full-text
Abstract
During the single crystal (SX) solidification of turbine blades, grain defects can form in the platform regions which have abruptly varying cross-sections. A high undercoolability of a Ni-based alloy prevents the growth of stray grains in the thermally undercooled platform area. To evaluate
[...] Read more.
During the single crystal (SX) solidification of turbine blades, grain defects can form in the platform regions which have abruptly varying cross-sections. A high undercoolability of a Ni-based alloy prevents the growth of stray grains in the thermally undercooled platform area. To evaluate the undercoolability of different Ni-based alloys, temperature measurements were conducted using the same thermal conditions in an Al2O3-SiO2 investment casting shell mold system. Furthermore, the results were compared with stray grains in directionally solidified components. Full article
(This article belongs to the Special Issue Superalloys)
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Open AccessArticle Microstructures and Wear Performance of PTAW Deposited Ni-Based Coatings with Spherical Tungsten Carbide
Metals 2015, 5(4), 1984-1996; doi:10.3390/met5041984
Received: 26 August 2015 / Revised: 26 September 2015 / Accepted: 20 October 2015 / Published: 26 October 2015
Cited by 2 | PDF Full-text (1669 KB) | HTML Full-text | XML Full-text
Abstract
The Ni-based coatings with different content of spherical tungsten carbide were deposited by plasma transfer arc welding (PTAW) method on 304 austenitic stainless steel sheets in this study. The microstructure and wear property of spherical tungsten carbide particle reinforced composite coatings were investigated
[...] Read more.
The Ni-based coatings with different content of spherical tungsten carbide were deposited by plasma transfer arc welding (PTAW) method on 304 austenitic stainless steel sheets in this study. The microstructure and wear property of spherical tungsten carbide particle reinforced composite coatings were investigated by means of optical microscope, scanning electron microscope (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA) and sliding wear test. It is shown that the fraction of spherical tungsten carbides has an important influence on microstructure of Ni-based overlay. The Ni40 overlay consists of γ-Ni dendrites with interdendritic Ni-based eutectics, borides and carbides improving the wear resistance. In the case of composite coatings with different content of tungsten carbide, many new phases are observed, such as Ni2W4C and NiW. In addition, there are a large number of irregular structures in composite coatings, such as acicular structure and irregular stripe organization. The results of sliding wear test indicate that the mass loss of coatings is influenced by the content of tungsten carbide. The mass loss decreases with the increase of tungsten carbide fraction. At high load, the abrasive resistance of composite coating with 60 wt. % tungsten carbide is improved about 50-fold compared to that of Ni40 overlay. Full article
(This article belongs to the Special Issue Superalloys)
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