Editorial

4 pages, 205 KiB

Open AccessEditorial

Special Issue “Advanced Refractory Alloys”: Metals, MDPI

by Oleg N. Senkov, Panagiotis (Panos) Tsakiropoulos and Jean-Philippe Couzinié

Metals 2022, 12(2), 333; https://doi.org/10.3390/met12020333 - 14 Feb 2022

Cited by 5 | Viewed by 1701

Metallic materials with extreme and often unusual combinations of properties are always in high demand in the competitive world market [...] Full article

(This article belongs to the Special Issue Advanced Refractory Alloys)

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8 pages, 4053 KiB

Open AccessEditor’s ChoiceArticle

Effect of V and Ti on the Oxidation Resistance of WMoTaNb Refractory High-Entropy Alloy at High Temperatures

by Shuaidan Lu, Xiaoxiao Li, Xiaoyu Liang, Wei Yang and Jian Chen

Metals 2022, 12(1), 41; https://doi.org/10.3390/met12010041 - 25 Dec 2021

Cited by 14 | Viewed by 2983

Abstract

Alloying with V and Ti elements effectively improves the strength of WMoTaNb refractory high entropy alloys (RHEAs) at elevated temperatures. However, their effects on the oxidation resistance of WMoTaNb RHEAs are unknown, which is vitally important to their application at high temperatures. In [...] Read more.

Alloying with V and Ti elements effectively improves the strength of WMoTaNb refractory high entropy alloys (RHEAs) at elevated temperatures. However, their effects on the oxidation resistance of WMoTaNb RHEAs are unknown, which is vitally important to their application at high temperatures. In this work, the effect of V and Ti on the oxidation behavior of WMoTaNb RHEA at 1000 °C was investigated using a thermogravimetric system, X-ray diffraction and scanning electron microscopy. The oxidation of all alloys was found to obey a power law passivating oxidation at the early stage. The addition of V aggravates the volatility of V₂O₅, MoO₃ and WO₃, and leads to disastrous internal oxidation. The addition of Ti reduces the mass gain in forming the full coverage of passivating scale and prolongs the passivation duration of alloys. Full article

(This article belongs to the Special Issue Advanced Refractory Alloys)

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34 pages, 8955 KiB

Open AccessFeature PaperArticle

On the Microstructure and Properties of the Nb-23Ti-5Si-5Al-5Hf-5V-2Cr-2Sn (at.%) Silicide-Based Alloy—RM(Nb)IC

by Nikos Vellios, Paul Keating and Panos Tsakiropoulos

Metals 2021, 11(11), 1868; https://doi.org/10.3390/met11111868 - 20 Nov 2021

Cited by 13 | Viewed by 2069

Abstract

The microstructure, isothermal oxidation, and hardness of the Nb-23Ti-5Si-5Al-5Hf-5V-2Cr-2Sn alloy and the hardness and Young’s moduli of elasticity of its Nb_ss and Nb₅Si₃ were studied. The alloy was selected using the niobium intermetallic composite elaboration (NICE) alloy design methodology. [...] Read more.

The microstructure, isothermal oxidation, and hardness of the Nb-23Ti-5Si-5Al-5Hf-5V-2Cr-2Sn alloy and the hardness and Young’s moduli of elasticity of its Nb_ss and Nb₅Si₃ were studied. The alloy was selected using the niobium intermetallic composite elaboration (NICE) alloy design methodology. There was macrosegregation of Ti and Si in the cast alloy. The Nb_ss, αNb₅Si₃, γNb₅Si₃, and HfO₂ phases were present in the as-cast or heat-treated alloy plus TiN in the near-the-surface areas of the latter. The vol.% of Nb_ss was about 80%. There were Ti- and Ti-and-Hf-rich areas in the solid solution and the 5-3 silicide, respectively, and there was a lamellar microstructure of these two phases. The V partitioned to the Nb_ss, where the solubilities of Al, Cr, Hf, and V increased with increasing Ti concentration. At 700, 800, and 900 °C, the alloy did not suffer from catastrophic pest oxidation; it followed parabolic oxidation kinetics in the former two temperatures and linear oxidation kinetics in the latter, where its mass change was the lowest compared with other Sn-containing alloys. An Sn-rich layer formed in the interface between the scale and the substrate, which consisted of the Nb₃Sn and Nb₆Sn₅ compounds at 900 °C. The latter compound was not contaminated with oxygen. Both the Nb_ss and Nb₅Si₃ were contaminated with oxygen, with the former contaminated more severely than the latter. The bulk of the alloy was also contaminated with oxygen. The alloying of the Nb_ss with Sn increased its elastic modulus compared with Sn-free solid solutions. The hardness of the alloy, its Nb_ss, and its specific room temperature strength compared favourably with many refractory metal-complex-concentrated alloys (RCCAs). The agreement of the predictions of NICE with the experimental results was satisfactory. Full article

(This article belongs to the Special Issue Advanced Refractory Alloys)

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22 pages, 10857 KiB

Open AccessArticle

Effect of Re on the Microstructure and Mechanical Properties of NbTiZr and TaTiZr Equiatomic Alloys

by Oleg N. Senkov, Stéphane Gorsse, Robert Wheeler, Eric J. Payton and Daniel B. Miracle

Metals 2021, 11(11), 1819; https://doi.org/10.3390/met11111819 - 12 Nov 2021

Cited by 6 | Viewed by 2038

Abstract

The microstructure, phase composition, and mechanical properties of NbTiZr, TaTiZr, Re_0.3NbTiZr, and Re_0.3TaTiZr are reported. The alloys were produced by vacuum arc melting and hot isostatically pressed (HIP’d) at 1400 °C for 3 h under 276 MPa hydrostatic pressure [...] Read more.

The microstructure, phase composition, and mechanical properties of NbTiZr, TaTiZr, Re_0.3NbTiZr, and Re_0.3TaTiZr are reported. The alloys were produced by vacuum arc melting and hot isostatically pressed (HIP’d) at 1400 °C for 3 h under 276 MPa hydrostatic pressure of high-purity argon prior to testing. NbTiZr had a single-phase BCC crystal structure, while TaTiZr had a Ti- and Zr-rich BCC matrix phase and Ta-rich nanometer-sized BCC precipitates, at volume fractions of 0.49 and 0.51, respectively. Re_0.3NbTiZr consisted of a BCC matrix phase and Re-rich precipitates with a FCC crystal structure and the volume fraction of 0.14. The microstructure of Re_0.3TaTiZr consisted of a Zr-rich BCC matrix phase and coarse, Re and Ta rich, BCC particles, which volume fraction was 0.47. NbTiZr and TaTiZr had a room temperature (RT) yield stress of 920 MPa and 1670 MPa, respectively. While, 10 at.% Re additions increased the RT yield stress to 1220 MPa in Re_0.3NbTiZr and 1715 MPa in Re_0.3TaTiZr. Re also considerably improved the RT ductility of TaTiZr, from about 2.5% to 10% of true strain. The positive strengthening effect from the Re additions was retained at high (800–1200 °C) temperatures. Full article

(This article belongs to the Special Issue Advanced Refractory Alloys)

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12 pages, 3243 KiB

Open AccessArticle

A Novel Alloy Development Approach: Biomedical Equiatomic Ta-Nb-Ti Alloy

by Maximilian Regenberg, Janett Schmelzer, Georg Hasemann, Jessica Bertrand and Manja Krüger

Metals 2021, 11(11), 1778; https://doi.org/10.3390/met11111778 - 04 Nov 2021

Cited by 2 | Viewed by 1714

Abstract

In the present manuscript, we report on the properties of an equiatomic Ta-Nb-Ti alloy as the basis for a novel, biomedical, multi-component alloy development. The alloy was produced using an arc melting furnace under Ar atmosphere, metallographically prepared, and investigated respectively. Furthermore, the [...] Read more.

In the present manuscript, we report on the properties of an equiatomic Ta-Nb-Ti alloy as the basis for a novel, biomedical, multi-component alloy development. The alloy was produced using an arc melting furnace under Ar atmosphere, metallographically prepared, and investigated respectively. Furthermore, the alloy produced, as well as samples of elemental Ta, Nb, alloy Co-28Cr-6Mo, and alloy Ti-6Al-4V, were prepared with defined 1200 grit SiC grinding paper. The topography of the surfaces was evaluated using confocal microscopy and contact angle measurements subsequently. Afterwards, the biocompatibility of the novel alloy Ta-Nb-Ti was evaluated by means of cell (osteoblast) attachment as well as monocyte inflammatory response analysis. First results indicate competitive osteoblast attachment, as well as comparable expressions of fibrosis markers in comparison to conventionally used biomedical materials. In addition, the Ta-Nb-Ti alloy showed a markedly reduced inflammatory capacity, indicating a high potential for use as a prospective biomedical material. Full article

(This article belongs to the Special Issue Advanced Refractory Alloys)

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13 pages, 7701 KiB

Open AccessArticle

Effects of Zr Content on the Microstructure and Performance of TiMoNbZr_x High-Entropy Alloys

by Gengbiao Chen, Yi Xiao, Xixi Ji, Xiubing Liang, Yongle Hu, Zhihai Cai, Jian Liu and Yonggang Tong

Metals 2021, 11(8), 1315; https://doi.org/10.3390/met11081315 - 19 Aug 2021

Cited by 9 | Viewed by 2370

Abstract

TiMoNbZr_x refractory high-entropy alloys were prepared by vacuum arc melting, and the influence of the Zr alloying element and its content on the phases, microstructure, mechanical properties, and wear resistance of TiMoNbZr_x alloys was explored. It was found that the alloys [...] Read more.

TiMoNbZr_x refractory high-entropy alloys were prepared by vacuum arc melting, and the influence of the Zr alloying element and its content on the phases, microstructure, mechanical properties, and wear resistance of TiMoNbZr_x alloys was explored. It was found that the alloys after Zr addition were composed of a single BCC phase. Upon increasing the Zr content, the grain size of the as-cast alloy decreased first and then increased, and TiMoNbZr_0.5 exhibited the smallest grain size. Adding an appropriate amount of Zr increased the strength and hardness of the alloys. TiMoNbZr_0.5 exhibited the best wear resistance, with a friction coefficient of about 0.33. It also displayed the widest wear scar, the shallowest depth, and the greatest degree of wear on the grinding ball because of the formation of an oxide film during wear. Full article

(This article belongs to the Special Issue Advanced Refractory Alloys)

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12 pages, 3513 KiB

Open AccessFeature PaperArticle

Orientation Dependence of High Cycle Fatigue Behavior of a <111> Oriented Single-Crystal Nickel-Based Superalloy

by Bin Hu, Yanling Pei, Shengkai Gong and Shusuo Li

Metals 2021, 11(8), 1248; https://doi.org/10.3390/met11081248 - 06 Aug 2021

Cited by 3 | Viewed by 1862

Abstract

High cycle fatigue failure has been recognized as one of the major forms of failure of aero-engine blades. This paper presents the high cycle fatigue testing of a Ni-based superalloy near <111> orientation at 800 °C. The fracture morphology and dislocation configuration were [...] Read more.

High cycle fatigue failure has been recognized as one of the major forms of failure of aero-engine blades. This paper presents the high cycle fatigue testing of a Ni-based superalloy near <111> orientation at 800 °C. The fracture morphology and dislocation configuration were analyzed in detail by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to indicate the influence of orientation deviation degree on the high cycle fatigue properties. The results show that the orientation deviation significantly affects the initiation of the slip systems, which is closely related to fatigue performance. The best fatigue life appears on the precise <111> orientation, and the deformation behavior is controlled by multiple sets of equivalent <110> {111} slip systems. With the increase in orientation deviation, the fatigue properties of the alloy degenerate significantly. On the boundary of <111>-<001>, two groups of <110> {111} slip systems with the maximum Schmid shear stress dominate the deformation behavior. On the other hand, on the <111>-<011> boundary, the formation of stacking faults and rapid cutting of γ’ precipitates results in a negative effect on the fatigue life. Full article

(This article belongs to the Special Issue Advanced Refractory Alloys)

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15 pages, 4450 KiB

Open AccessFeature PaperArticle

An Investigation of the Miscibility Gap Controlling Phase Formation in Refractory Metal High Entropy Superalloys via the Ti-Nb-Zr Constituent System

by Tamsin E. Whitfield, George J. Wise, Ed J. Pickering, Howard J. Stone and Nicholas G. Jones

Metals 2021, 11(8), 1244; https://doi.org/10.3390/met11081244 - 05 Aug 2021

Cited by 8 | Viewed by 2835

Abstract

Refractory metal high entropy superalloys (RSAs) have been heralded as potential new high temperature structural materials. They have nanoscale cuboidal bcc+B2 microstructures that are thought to form on quenching through a spinodal decomposition process driven by the Ta-Zr or Nb-Zr miscibility gaps, followed [...] Read more.

Refractory metal high entropy superalloys (RSAs) have been heralded as potential new high temperature structural materials. They have nanoscale cuboidal bcc+B2 microstructures that are thought to form on quenching through a spinodal decomposition process driven by the Ta-Zr or Nb-Zr miscibility gaps, followed by ordering of one of the bcc phases. However, it is difficult to isolate the role of different elemental interactions within compositionally complex RSAs. Therefore, in this work the microstructures produced by the Nb-Zr miscibility gap within the compositionally simpler Ti-Nb-Zr constituent system were investigated. A systematic series of alloys with compositions of Ti5Nb_xZr_95−x (x = 25–85 at.%) was studied following quenching from solution heat treatment and long duration thermal exposures at 1000, 900 and 700 °C for 1000 h. During exposures at 900 °C and above the alloys resided in a single bcc phase field. At 700 °C, alloys with 40–75 at.% Nb resided within a three phase bcc + bcc + hcp phase field and a large misfit, 4.7–5%, was present between the two bcc phases. Evidence of nanoscale cuboidal microstructures was not observed, even in slow cooled samples. Whilst it was not possible to conclusively determine whether a spinodal decomposition occurs within this ternary system, these insights suggest that Nb-Zr interactions may not play a significant role in the formation of the nanoscale cuboidal RSA microstructures during cooling. Full article

(This article belongs to the Special Issue Advanced Refractory Alloys)

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9 pages, 3584 KiB

Open AccessFeature PaperArticle

Tensile Creep Properties of Cr-Si Alloys at 980 °C in Air—Influence of Ge and Mo Addition

by Petra Pfizenmaier, Anke Silvia Ulrich, Mathias C. Galetz and Uwe Glatzel

Metals 2021, 11(7), 1072; https://doi.org/10.3390/met11071072 - 03 Jul 2021

Cited by 4 | Viewed by 1604

Abstract

The tensile creep behavior of Cr-Si alloys with Cr ≥ 91 at.% was investigated in air at 980 °C with a constant load of 50–100 MPa. Additionally, the influence of substitutional alloying additions of 2 at.% Ge and Mo, leading to ternary alloys [...] Read more.

The tensile creep behavior of Cr-Si alloys with Cr ≥ 91 at.% was investigated in air at 980 °C with a constant load of 50–100 MPa. Additionally, the influence of substitutional alloying additions of 2 at.% Ge and Mo, leading to ternary alloys was studied. The addition of Ge or Mo results in an improvement in creep strength, with the highest strength achieved with addition of Mo. For longer creep exposure times a strong effect is observed, because of severe nitrogen uptake from the air, depending on alloy composition. Based on the results a novel mechanism for the impact of chromium nitride formation on the creep behavior is proposed. Full article

(This article belongs to the Special Issue Advanced Refractory Alloys)

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