Observation of a refractory metal matrix containing Zr-Ti-rich precipitates in a Mo0.5NbTa0.5TiZr high entropy alloy

Whitfield, Tamsin; Pickering, Ed; Talbot, CEP; Jones, C.N.; Stone, H.J.; Jones, Nicholas Blurton

doi:10.1016/j.scriptamat.2020.01.028

Cited by 26 publications

(7 citation statements)

References 32 publications

(53 reference statements)

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“…The enrichment in refractory metal elements and reduction in Al is likely to stabilise a bcc structure [ 21 ]. In addition, since the formation of the nanoscale microstructure is primarily driven by the miscibility gap between Zr and refractory metals, the very low Zr content of the matrix phase is unlikely to result in such a phase separation [ 10 , 22 , 23 ]. These assertions are supported by other reports of the phase chemistries and structures identified in other RSA.…”

Section: Resultsmentioning

confidence: 99%

“…Hence, it is believed that following cooling to room temperature the composition of the matrix phase in AlMo 0.5 NbTa 0.5 TiZr meant that it maintained a bcc structure, unlike the matrix phase of AlMo 0.5 NbTa 0.5 TiZr 0.5, which was shown to have a B2 structure following cooling from the exposure temperature. The formation of the B2 phase also indicates that sufficient Al concentration must have been retained within the matrix of AlMo 0.5 NbTa 0.5 TiZr 0.5 to facilitate ordering [ 6 , 8 , 9 , 21 , 23 , 25 ]. The final, important, difference between these two studies was present within the microstructures following exposure at 800 °C.…”

Section: Resultsmentioning

confidence: 99%

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Microstructural Degradation of the AlMo0.5NbTa0.5TiZr Refractory Metal High-Entropy Superalloy at Elevated Temperatures

Whitfield

Stone

Jones

et al. 2021

Entropy

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Refractory metal high-entropy superalloys (RSA), which possess a nanoscale microstructure of B2 and bcc phases, have been developed to offer high temperature capabilities beyond conventional Ni-based alloys. Despite showing a number of excellent attributes, to date there has been little consideration of their microstructural stability, which is an essential feature of any material employed in high temperature service. Here, the stability of the exemplar RSA AlMo0.5NbTa0.5TiZr is studied following 1000 h exposures at 1200, 1000 and 800 °C. Crucially, the initial nanoscale cuboidal B2 + bcc microstructure was found to be unstable following the thermal exposures. Extensive intragranular precipitation of a hexagonal Al-Zr-rich intermetallic occurred at all temperatures and, where present, the bcc and B2 phases had coarsened and changed morphology. This microstructural evolution will concomitantly change both the mechanical and environmental properties and is likely to be detrimental to the in-service performance of the alloy.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Microstructural Degradation of the AlMo0.5NbTa0.5TiZr Refractory Metal High-Entropy Superalloy at Elevated Temperatures

Whitfield

Stone

Jones

et al. 2021

Entropy

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“…Mo0.5NbTa0.5TiZr RHEA, an ordered precipitate formed in the Ti-Zr rich matrix without Al disorder precipitates forming [38].…”

Section: Microstructure and Phasesmentioning

confidence: 99%

“…Another study was done on an ReTaWNbMo RHEA, and it was shown that as-cast alloys had a BCC crystal structure after annealing, but with increasing annealing temperature (673 K (400 • C), 873 K (600 • C), 1073 K (800 • C), and 1273 K (1000 • C)), coarse dendrites were transformed into equiaxed grains [37]. When Al was added to the Mo 0.5 NbTa 0.5 TiZr RHEA, an ordered precipitate formed in the Ti-Zr rich matrix without Al disorder precipitates forming [38].…”

Section: Mechanical Behaviormentioning

confidence: 99%

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

et al. 2021

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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.

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“…However, despite significant global research activity, several key challenges remain in the development of commercially viable RSAs. Among these challenges, it is generally accepted that greater control over the microstructural formation is required in order to produce materials with a ductile bcc matrix phase and stable superlattice precipitates [2,5,[7][8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

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

Whitfield

Wise

Pickering

et al. 2021

Metals

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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 Ti5NbxZr95−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.

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Observation of a refractory metal matrix containing Zr-Ti-rich precipitates in a Mo0.5NbTa0.5TiZr high entropy alloy

Cited by 26 publications

References 32 publications

Microstructural Degradation of the AlMo0.5NbTa0.5TiZr Refractory Metal High-Entropy Superalloy at Elevated Temperatures

Microstructural Degradation of the AlMo0.5NbTa0.5TiZr Refractory Metal High-Entropy Superalloy at Elevated Temperatures

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

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

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