On the Microstructure and Properties of Nb-Ti-Cr-Al-B-Si-X (X = Hf, Sn, Ta) Refractory Complex Concentrated Alloys

We studied the effect of the addition of Hf, Sn, or Ta on the density, macrosegregation, microstructure, hardness and oxidation of three refractory metal intermetallic composites based on Nb (RM(Nb)ICs) that were also complex concentrated alloys (i.e., RM(Nb)ICs/RCCAs), namely, the alloys TT5, TT6, and TT7, which had the nominal compositions (at.%) Nb-24Ti-18Si-5Al-5B-5Cr-6Ta, Nb-24Ti-18Si-4Al-6B-5Cr-4Sn and Nb-24Ti-17Si-5Al-6B-5Cr-5Hf, respectively. The alloys were compared with B containing and B free RM(Nb)ICs. The macrosegregation of B, Ti, and Si was reduced with the addition, respectively of Hf, Sn or Ta, Sn or Ta, and Hf or Sn. All three alloys had densities less than 7 g/cm3. The alloy TT6 had the highest specific strength in the as cast and heat-treated conditions, which was also higher than that of RCCAs and refractory metal high entropy alloys (RHEAs). The bcc solid solution Nbss and the tetragonal T2 and hexagonal D88 silicides were stable in the alloys TT5 and TT7, whereas in TT6 the stable phases were the A15-Nb3Sn and the T2 and D88 silicides. All three alloys did not pest at 800 °C, where only the scale that was formed on TT5 spalled off. At 1200 °C, the scale of TT5 spalled off, but not the scales of TT6 and TT7. Compared with the B free alloys, the synergy of B with Ta was the least effective regarding oxidation at 800 and 1200 °C. Macrosegregation of solutes, the chemical composition of phases, the hardness of the Nbss and the alloys, and the oxidation of the alloys at 800 and 1200 °C were considered from the perspective of the Niobium Intermetallic Composite Elaboration (NICE) alloy design methodology. Relationships between properties and the parameters VEC, δ, and Δχ of alloy or phase and between parameters were discussed. The trends of parameters and the location of alloys and phases in parameter maps were in agreement with NICE.

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Refractory Metal (Nb) Intermetallic Composites, High Entropy Alloys, Complex Concentrated Alloys and the Alloy Design Methodology NICE—Mise-en-scène † Patterns of Thought and Progress

Materials ◽

10.3390/ma14040989 ◽

2021 ◽

Vol 14 (4) ◽

pp. 989

Author(s):

Panos Tsakiropoulos

Keyword(s):

Solid Solution ◽

Refractory Metal ◽

Design Methodology ◽

Alloy Design ◽

High Entropy Alloys ◽

Laves Phases ◽

High Entropy ◽

High Temperature Materials ◽

Mise En Scene ◽

Intermetallic Composite

The paper reflects on the usefulness of the alloy design methodology NICE (Niobium Intermetallic Composite Elaboration) for the development of new Nb-containing metallic ultra-high-temperature materials (UHTMs), namely refractory metal (Nb) intermetallic composites (RM(Nb)ICs), refractory high entropy alloys (RHEAs) and refractory complex concentrated alloys (RCCAs), in which the same phases can be present, specifically bcc solid solution(s), M5Si3 silicide(s) and Laves phases. The reasons why a new alloy design methodology was sought and the foundations on which NICE was built are discussed. It is shown that the alloying behavior of RM(Nb)ICs, RHEAs and RCCAs can be described by the same parameters. The practicality of parameter maps inspired by NICE for describing/understanding the alloying behavior and properties of alloys and their phases is demonstrated. It is described how NICE helps the alloy developer to understand better the alloys s/he develops and what s/he can do and predict (calculate) with NICE. The paper expands on RM(Nb)ICs, RHEAs and RCCAs with B, Ge or Sn, the addition of which and the presence of A15 compounds is recommended in RHEAs and RCCAs to achieve a balance of properties.

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The Effect of Boron on the Microstructure and Properties of Refractory Metal Intermetallic Composites (RM(Nb)ICs) Based on Nb-24Ti-xSi (x = 16, 17 or 18 at.%) with Additions of Al, Cr or Mo

Materials ◽

10.3390/ma14206101 ◽

2021 ◽

Vol 14 (20) ◽

pp. 6101

Author(s):

Tophan Thandorn ◽

Panos Tsakiropoulos

Keyword(s):

Refractory Metal ◽

Design Methodology ◽

Room Temperature ◽

High Entropy Alloys ◽

Scale Spallation ◽

High Entropy ◽

Specific Strength ◽

Arc Melting ◽

High Temperature Materials ◽

Heat Treated

This paper is about metallic ultra-high temperature materials, in particular, refractory metal intermetallic composites based on Nb, i.e., RM(Nb)ICs, with the addition of boron, which are compared with refractory metal high entropy alloys (RHEAs) or refractory metal complex concentrated alloys (RCCAs). We studied the effect of B addition on the density, macrosegregation, microstructure, hardness and oxidation of four RM(Nb)IC alloys, namely the alloys TT2, TT3, TT4 and TT8 with nominal compositions (at.%) Nb-24Ti-16Si-5Cr-7B, Nb-24Ti-16Si-5Al-7B, Nb-24Ti-18Si-5Al-5Cr-8B and Nb-24Ti-17Si-3.5Al-5Cr-6B-2Mo, respectively. The alloys made it possible to compare the effect of B addition on density, hardness or oxidation with that of Ge or Sn addition. The alloys were made using arc melting and their microstructures were characterised in the as cast and heat-treated conditions. The B macrosegregation was highest in TT8. The macrosegregation of Si or Ti increased with the addition of B and was lowest in TT8. The alloy TT8 had the lowest density of 6.41 g/cm3 and the highest specific strength at room temperature, which was also higher than that of RCCAs and RHEAs. The Nbss and T2 silicide were stable in the alloys TT2 and TT3, whereas in TT4 and TT8 the stable phases were the Nbss and the T2 and D88 silicides. Compared with the Ge or Sn addition in the same reference alloy, the B and Ge addition was the least and most effective at 800 °C (i.e., in the pest regime), when no other RM was present in the alloy. Like Ge or Sn, the B addition in TT2, TT3 and TT4 did not suppress scale spallation at 1200 °C. Only the alloy TT8 did not pest and its scales did not spall off at 800 and 1200 °C. The macrosegregation of Si and Ti, the chemical composition of Nbss and T2, the microhardness of Nbss and the hardness of alloys, and the oxidation of the alloys at 800 and 1200 °C were also viewed from the perspective of the alloy design methodology NICE and relationships with the alloy or phase parameters VEC, δ and Δχ. The trends of these parameters and the location of alloys and phases in parameter maps were found to be in agreement with NICE.

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Microstructure and Mechanical Properties of TaNbVTiAlx Refractory High-Entropy Alloys

Entropy ◽

10.3390/e22030282 ◽

2020 ◽

Vol 22 (3) ◽

pp. 282 ◽

Cited By ~ 1

Author(s):

Li Xiang ◽

Wenmin Guo ◽

Bin Liu ◽

Ao Fu ◽

Jianbo Li ◽

...

Keyword(s):

Mechanical Properties ◽

Solid Solution ◽

High Entropy Alloys ◽

Strengthening Effect ◽

High Entropy ◽

Solid Solution Strengthening ◽

Specific Strength ◽

Compression Properties ◽

Uniform Microstructure ◽

Solution Strengthening

A series of TaNbVTiAlx (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) refractory high-entropy alloys (RHEAs) with high specific strength and reasonable plasticity were prepared using powder metallurgy (P/M) technology. This paper studied their microstructure and compression properties. The results show that all the TaNbVTiAlx RHEAs exhibited a single BCC solid solution microstructure with no elemental segregation. The P/M TaNbVTiAlx RHEAs showed excellent room-temperature specific strength (207.11 MPa*cm3/g) and high-temperature specific strength (88.37 MPa*cm3/g at 900 °C and 16.03 MPa*cm3/g at 1200 °C), with reasonable plasticity, suggesting that these RHEAs have potential to be applied at temperatures >1200 °C. The reasons for the excellent mechanical properties of P/M TaNbVTiAl0.2 RHEA were the uniform microstructure and solid solution strengthening effect.

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Lattice distortion as an estimator of solid solution strengthening in high-entropy alloys

Materials Characterization ◽

10.1016/j.matchar.2021.110877 ◽

2021 ◽

pp. 110877

Author(s):

Ankit Roy ◽

Praveen Sreeramagiri ◽

Tomas Babuska ◽

Brandon Krick ◽

Pratik K. Ray ◽

...

Keyword(s):

Solid Solution ◽

Lattice Distortion ◽

High Entropy Alloys ◽

High Entropy ◽

Solid Solution Strengthening ◽

Solution Strengthening

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Machine learning-enabled identification of new medium to high entropy alloys with solid solution phases

Computational Materials Science ◽

10.1016/j.commatsci.2021.110623 ◽

2021 ◽

Vol 197 ◽

pp. 110623

Author(s):

Ujjawal Kumar Jaiswal ◽

Yegi Vamsi Krishna ◽

M.R. Rahul ◽

Gandham Phanikumar

Keyword(s):

Machine Learning ◽

Solid Solution ◽

High Entropy Alloys ◽

High Entropy

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A new infinite solid solution strategy to design eutectic high entropy alloys with B2 and BCC structure

Scripta Materialia ◽

10.1016/j.scriptamat.2021.113886 ◽

2021 ◽

Vol 199 ◽

pp. 113886

Author(s):

Xicong Ye ◽

Jinyan Xiong ◽

Xin Wu ◽

Chang Liu ◽

Dong Xu ◽

...

Keyword(s):

Solid Solution ◽

High Entropy Alloys ◽

Solution Strategy ◽

High Entropy ◽

Bcc Structure

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A review on phase prediction in high entropy alloys

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/09544062211008935 ◽

2021 ◽

pp. 095440622110089

Author(s):

Vinay Kumar Soni ◽

S Sanyal ◽

K Raja Rao ◽

Sudip K Sinha

Keyword(s):

Solid Solution ◽

Phase Formation ◽

Single Phase ◽

High Entropy Alloy ◽

High Entropy Alloys ◽

Modeling Tools ◽

High Entropy ◽

Recent Developments ◽

Phase Prediction ◽

The Stability

The formation of single phase solid solution in High Entropy Alloys (HEAs) is essential for the properties of the alloys therefore, numerous approach were proposed by many researchers to predict the stability of single phase solid solution in High Entropy Alloy. The present review examines some of the recent developments while using computational intelligence techniques such as parametric approach, CALPHAD, Machine Learning etc. for prediction of various phase formation in multicomponent high entropy alloys. A detail study of this data-driven approaches pertaining to the understanding of structural and phase formation behaviour of a new class of compositionally complex alloys is done in the present investigation. The advantages and drawbacks of the various computational are also discussed. Finally, this review aims at understanding several computational modeling tools complying the thermodynamic criteria for phase formation of novel HEAs which could possibly deliver superior mechanical properties keeping an aim at advanced engineering applications.

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Al, Cu and Zr Addition to High Entropy Alloys: The Effect on Recrystallization Temperature

Materials Science Forum ◽

10.4028/www.scientific.net/msf.941.1137 ◽

2018 ◽

Vol 941 ◽

pp. 1137-1142

Author(s):

Elena Colombini ◽

Andrea Garzoni ◽

Roberto Giovanardi ◽

Paolo Veronesi ◽

Angelo Casagrande

Keyword(s):

Solid Solution ◽

Grain Size ◽

Single Phase ◽

Boundary Energy ◽

Cold Deformation ◽

Recrystallization Temperature ◽

High Entropy Alloys ◽

High Entropy ◽

Ni Alloy ◽

Sluggish Diffusion

The equimolar Cr, Mn, Fe, Co and Ni alloy, first produced in 2004, was unexpectedly found to be single-phase. Consequently, a new concept of materials was developed: high entropy alloys (HEA) forming a single solid-solution with a near equiatomic composition of the constituting elements. In this study, an equimolar CoCrFeMnNi HEA was modified by the addition of 5 at% of either Al, Cu or Zr. The cold-rolled alloys were annealed for 30 minutes at high temperature to investigate the recrystallization kinetics. The evolution of the grain boundary and the grain size were investigated, from the as-cast to the recrystallized state. Results show that the recrystallized single phase FCC structures exhibits different twin grains density, grain size and recrystallization temperatures as a function of the at.% of modifier alloying elements added. In comparison to the equimolar CoCrFeMnNi, the addition of modifier elements increases significantly the recrystallization temperature after cold deformation. The sluggish diffusion (typical of HEA alloys), the presence of a solute in solid solution as well as the low twin boundary energy are responsible for the lower driving force for recrystallization.

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