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17 pages, 5012 KiB

Open AccessArticle

Oxidation and Microstructural Behaviors of Ni-Based Alloys Strengthened by (Ta, Hf)C Carbides at 1250 °C in Air

by Patrice Berthod, Dame Assane Kane and Lionel Aranda

Crystals 2021, 11(2), 159; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11020159 - 05 Feb 2021

Cited by 2 | Viewed by 1681

Two alloys based on nickel and designed to be reinforced by MC carbides thanks to the presence of Hf and Ta were produced by casting. They were subjected to 50 h-long isothermal exposure at 1250 °C in synthetic air with thermogravimetric monitoring of [...] Read more.

Two alloys based on nickel and designed to be reinforced by MC carbides thanks to the presence of Hf and Ta were produced by casting. They were subjected to 50 h-long isothermal exposure at 1250 °C in synthetic air with thermogravimetric monitoring of the oxidation progress. In the as-cast state, they contain both significant quantities of (Hf,Ta)C carbides. Their verified melting start temperatures, close to 1300 °C, allowed performing the planned oxidation test. The two alloys demonstrated a chromia-forming behavior with limited mass gain rates. However, they also showed a rather low resistance to oxide spallation at cooling, which is in proportion with the Ta/Hf ratio. After 50 h at 1250 °C, the morphology of the carbides had significantly evolved, from their initial script-like shape to a fragmented and coalesced state. The results are promising, but the use of these alloys at 1250 °C needs further improvements on the mechanical level. Full article

(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)

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12 pages, 1925 KiB

Open AccessArticle

Origins of a Low-Sulfur Superalloy Al₂O₃ Scale Adhesion Map

by James Smialek

Crystals 2021, 11(1), 60; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11010060 - 13 Jan 2021

Cited by 9 | Viewed by 1938

Abstract

Low-sulfur single-crystal Ni-base superalloys have demonstrated excellent cyclic oxidation resistance due to improved Al₂O₃ scale adhesion. This derives from preventing deleterious interfacial sulfur segregation that occurs at common ppm levels of S impurity. Multiple hydrogen-annealing desulfurization treatments were employed to [...] Read more.

Low-sulfur single-crystal Ni-base superalloys have demonstrated excellent cyclic oxidation resistance due to improved Al₂O₃ scale adhesion. This derives from preventing deleterious interfacial sulfur segregation that occurs at common ppm levels of S impurity. Multiple hydrogen-annealing desulfurization treatments were employed to produce a continuum of levels demonstrating this oxidative transition, using 1 h cyclic oxidation at 1100 °C for 500 h to 1000 h. The sulfur content was determined by glow discharge mass spectrometry. The complete gravimetric database of 25 samples is revealed and correlated with sulfur content. Maximum adhesion (i.e., no weight loss) was achieved at ≤ 0.3 ppmw S, significant spallation (20–30 mg/cm²) above 2 ppmw, with transitional behavior between 0.3 and 2 ppmw S. A map suggested that adhesion was enabled when the total sulfur reservoir was less than one S atom per Ni interface atom. Equilibrium models further suggest that segregation may be minimized (~1% at 0.2 ppmw bulk), regardless of section thickness. 1st order adhesion effects have thus been demonstrated for PWA 1480 having no Y, Zr, or Hf reactive element dopants and no possibility of confounding reactive element effects. The results are compared with 2nd generation PWA 1484, Rene’N5, N6, and CMSX-4^® SLS, all having Hf dopants. Full article

(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)

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14 pages, 5679 KiB

Open AccessArticle

Effect of Transition Metals Oxides on the Physical and Mechanical Properties of Sintered Tungsten Heavy Alloys

by Ayman H. Elsayed, Mohamed A. Sayed, Osama M. Dawood and Walid M. Daoush

Crystals 2020, 10(9), 825; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10090825 - 17 Sep 2020

Cited by 3 | Viewed by 2614

Abstract

The addition of transition element oxides to tungsten heavy alloys (WHAs) fabricated by powder metallurgy technique provides new materials with higher density and electrical conductivity, which may be adequate in some applications such as kinetic energy penetrators. Additionally, materials with higher electrical conductivity [...] Read more.

The addition of transition element oxides to tungsten heavy alloys (WHAs) fabricated by powder metallurgy technique provides new materials with higher density and electrical conductivity, which may be adequate in some applications such as kinetic energy penetrators. Additionally, materials with higher electrical conductivity are required for electrical contact applications such as electrical discharge machining (EDM) electrode materials. WHAs were fabricated by compacting its mixed constituents followed by sintering. Ni, Co and Fe are used as binding phases of the tungsten particles and oxides of Zr, Ti and Y are used as oxide dispersing strengthening (ODS) agents of the sintered materials. The results show that all of the chosen factors (i.e., pressure of compaction process, temperature of sintering, type of binding material and type of oxide) have clear effects on all properties of ODS tungsten heavy alloy specimens. The density and electrical conductivity increase with the increase in sintering temperature. Hardness and compression strength were also measured to evaluate the mechanical properties of sintered samples. Full article

(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)

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13 pages, 10437 KiB

Open AccessArticle

High-Temperature Mechanical Properties of IN718 Alloy: Comparison of Additive Manufactured and Wrought Samples

by Trunal Bhujangrao, Fernando Veiga, Alfredo Suárez, Edurne Iriondo and Franck Girot Mata

Crystals 2020, 10(8), 689; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10080689 - 09 Aug 2020

Cited by 39 | Viewed by 5479

Abstract

Wire Arc Additive Manufacturing (WAAM) is one of the most appropriate additive manufacturing techniques for producing large-scale metal components with a high deposition rate and low cost. Recently, the manufacture of nickel-based alloy (IN718) using WAAM technology has received increased attention due to [...] Read more.

Wire Arc Additive Manufacturing (WAAM) is one of the most appropriate additive manufacturing techniques for producing large-scale metal components with a high deposition rate and low cost. Recently, the manufacture of nickel-based alloy (IN718) using WAAM technology has received increased attention due to its wide application in industry. However, insufficient information is available on the mechanical properties of WAAM IN718 alloy, for example in high-temperature testing. In this paper, the mechanical properties of IN718 specimens manufactured by the WAAM technique have been investigated by tensile tests and hardness measurements. The specific comparison is also made with the wrought IN718 alloy, while the microstructure was assessed by scanning electron microscopy and X-ray diffraction analysis. Fractographic studies were carried out on the specimens to understand the fracture behavior. It was shown that the yield strength and hardness of WAAM IN718 alloy is higher than that of the wrought alloy IN718, while the ultimate tensile strength of the WAAM alloys is difficult to assess at lower temperatures. The microstructure analysis shows the presence of precipitates (laves phase) in WAAM IN718 alloy. Finally, the effect of precipitation on the mechanical properties of the WAAM IN718 alloy was discussed in detail. Full article

(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)

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9 pages, 5089 KiB

Open AccessArticle

Influence of Phosphorus Addition on the Stress Rupture Properties of Direct Aged IN706 Superalloy

by Sha Zhang, Anwen Zhang, Chaochao Xue, Dan Jia, Weiwei Zhang, Weiyang Wang, Xin Xin and Wenru Sun

Crystals 2020, 10(8), 641; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10080641 - 24 Jul 2020

Cited by 3 | Viewed by 2098

Abstract

This study investigated the influence of phosphorus (P) addition on the stress rupture properties of direct aged IN706 superalloy. The results showed that P slightly improved the stress rupture life of the superalloy when added in the range between 0.002% and 0.008%; however, [...] Read more.

This study investigated the influence of phosphorus (P) addition on the stress rupture properties of direct aged IN706 superalloy. The results showed that P slightly improved the stress rupture life of the superalloy when added in the range between 0.002% and 0.008%; however, it significantly reduced the stress rupture life when added in the range between 0.013% and 0.017%. Microstructure characterization indicated that the precipitation of γ′, γ″, and η phases was not significantly affected by the addition of P. Phosphides precipitated in the alloy containing 0.017% P after aging at 980 °C for 10 min. Compared to a similar study previously made on IN706 superalloy, it was found that the optimum P concentration in the as-solutioned state for improving the stress rupture properties was not definite. Furthermore, the relationship between the amount of P segregated at the grain boundary and the role of P on the stress rupture properties was discussed. Full article

(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)

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14 pages, 6223 KiB

Open AccessArticle

Processing, Microstructures and Mechanical Properties of a Ni-Based Single Crystal Superalloy

by Qingqing Ding, Hongbin Bei, Xinbao Zhao, Yanfei Gao and Ze Zhang

Crystals 2020, 10(7), 572; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10070572 - 03 Jul 2020

Cited by 24 | Viewed by 4943

Abstract

A second-generation Ni-based superalloy has been directionally solidified by using a Bridgman method, and the key processing steps have been investigated with a focus on their effects on microstructure evolution and mechanical properties. The as-grown microstructure is of a typical dendrite structure with [...] Read more.

A second-generation Ni-based superalloy has been directionally solidified by using a Bridgman method, and the key processing steps have been investigated with a focus on their effects on microstructure evolution and mechanical properties. The as-grown microstructure is of a typical dendrite structure with microscopic elemental segregation during solidification. Based on the microstructural evidence and the measured phase transformation temperatures, a step-wise solution treatment procedure is designed to effectively eliminate the compositional and microstructural inhomogeneities. Consequently, the homogenized microstructure consisting of γ/γ′ phases (size of γ′ cube is ~400 nm) have been successfully produced after a two-step (solid solution and aging) treatment. The mechanical properties of the resulting alloys with desirable microstructures at room and elevated temperatures are measured by tensile tests. The strength of the alloy is comparable to commercial monocrystalline superalloys, such as DD6 and CMSX-4. The fracture modes of the alloy at various temperatures have also been studied and the corresponding deformation mechanisms are discussed. Full article

(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)

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17 pages, 9766 KiB

Open AccessArticle

Microstructure Heredity of Inconel 718 Nickel-Based Superalloy during Preheating and Following Deformation

by Jianguo Wang, Dong Liu, Xiao Ding, Haiping Wang, Hai Wang, Jingqing Chen and Yanhui Yang

Crystals 2020, 10(4), 303; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10040303 - 15 Apr 2020

Cited by 6 | Viewed by 2721

Abstract

Preheating and compression tests of Inconel 718 superalloy double cone specimens were carried out to investigate the microstructure heredity during hot working. Optical microscopy, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were used to characterize the microstructure [...] Read more.

Preheating and compression tests of Inconel 718 superalloy double cone specimens were carried out to investigate the microstructure heredity during hot working. Optical microscopy, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were used to characterize the microstructure evolution. The results show that intense microstructure heredity can be found at the temperature 960~990 °C. During the preheating process, δ phase precipitation or grain growth could increase the fraction of high angle grain boundary (HAGBs) and Σ3ⁿ boundaries. Otherwise, the generation or spread of annealing twin could increase the fraction of LAGBs, Volume fraction of recrystallized grains was evaluated at the whole hot working process. At the temperature of 960~990 °C, the volume fraction of recrystallized grains increases with effective strain increasing. At the super solution temperature of δ phase, the volume fraction of recrystallized grains decreases and then increases with the increase of the effective strain. The unimodal grain size distribution and fully recrystallized grains can be obtained at low strains at 960~990 °C. The twin boundary length fraction of deformed specimens is always lower than that of preheated ones. Discontinuous dynamic recrystallization (DDRX) was considered as the dominant nucleation mechanism, and continuous dynamic recrystallization (CDRX) was strengthened with the increasing grain size. Twin introduced deformation will be the main deformation mode for alloy 718 with larger grain. Full article

(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)

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Review

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15 pages, 1400 KiB

Open AccessEditor’s ChoiceReview

A Review of the Latest Developments in the Field of Refractory High-Entropy Alloys

by Muthe Srikanth, A. Raja Annamalai, A. Muthuchamy and Chun-Ping Jen

Crystals 2021, 11(6), 612; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst11060612 - 28 May 2021

Cited by 48 | Viewed by 7311

Abstract

This review paper provides insight into current developments in refractory high-entropy alloys (RHEAs) based on previous and currently available literature. High-temperature strength, high-temperature oxidation resistance, and corrosion resistance properties make RHEAs unique and stand out from other materials. RHEAs mainly contain refractory elements [...] Read more.

This review paper provides insight into current developments in refractory high-entropy alloys (RHEAs) based on previous and currently available literature. High-temperature strength, high-temperature oxidation resistance, and corrosion resistance properties make RHEAs unique and stand out from other materials. RHEAs mainly contain refractory elements like W, Ta, Mo, Zr, Hf, V, and Nb (each in the 5–35 at% range), and some low melting elements like Al and Cr at less than 5 at%, which were already developed and in use for the past two decades. These alloys show promise in replacing Ni-based superalloys. In this paper, various manufacturing processes like casting, powder metallurgy, metal forming, thin-film, and coating, as well as the effect of different alloying elements on the microstructure, phase formation, mechanical properties and strengthening mechanism, oxidation resistance, and corrosion resistance, of RHEAs are reviewed. Full article

(This article belongs to the Special Issue Recent Advances in Metallurgy and Properties of Superalloys)

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