scholarly journals Microstructures and Isothermal Oxidation of the Alumina Scale Forming Nb1.7Si2.4Ti2.4Al3Hf0.5 and Nb1.3Si2.4Ti2.4Al3.5Hf0.4 Alloys

Materials ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 222 ◽  
Author(s):  
Mohammad Ghadyani ◽  
Claire Utton ◽  
Panos Tsakiropoulos
Keyword(s):  
Solid Solution ◽  
Internal Oxidation ◽  
Mixed Oxides ◽  
Alumina Scale ◽  
Isothermal Oxidation ◽  
Solid Solution Phase ◽  
High Entropy ◽  
Definition Of ◽  
Α Al2o3 ◽  
Range Of Values

Nb–silicide based alloy will require some kind of coating system. Alumina forming alloys that are chemically compatible with the Nb–silicide based alloy substrate could be components of such systems. The intermetallic alloys Nb1.7Si2.4Ti2.4Al3Hf0.5 and Nb1.3Si2.4Ti2.4Al3.5Hf0.4 were studied in the cast, heat treated and isothermally oxidised conditions at 800 and 1200 °C to find out if they are alumina scale formers. The alloys were designed using the alloy design methodology NICE and were required (i) not to have stable solid solution phase in their microstructures; (ii) not to pest and (iii) to form alumina scale. Their microstructures consisted of silicides and aluminides. Both alloys satisfied (i) and (ii) and formed thin scales at 800 °C. At 1200 °C the former alloy suffered from internal oxidation and formed alumina intermixed with Ti rich oxide beneath a thick “layered” scale of mixed oxides that contained Ti and/or Al and/or Si. There was no internal oxidation in the latter alloy that formed a thin continuous well adhering α-Al2O3 scale that was able to repair itself during oxidation at 1200 °C. In both alloys there was severe macrosegregation of Si, which in Nb1.3Si2.4Ti2.4Al3.5Hf0.4 was almost double that in Nb1.7Si2.4Ti2.4Al3Hf0.5. The severe macrosegregation of Si contributed to the formation of a “layered” structure in the former alloy that was retained at 800 and 1200 °C. Both alloys met the “standard definition” of High Entropy Alloys (HEAs). Compared with the range of values of the parameters valence band (VEC), δ and Δχ of bcc solid solution plus intermetallic(s) HEAs, only the Δχ of the alloy Nb1.7Si2.4Ti2.4Al3Hf0.5 was within the range and the parameters VEC and δ of both alloys respectively were outside and within the corresponding ranges. The alloy Nb1.3Si2.4Ti2.4Al3.5Hf0.4 exhibited strong correlations between the parameters Δχ, δ and VEC, and the range of values of each parameter was wider compared with the alloy Nb1.7Si2.4Ti2.4Al3Hf0.5. There was a strong correlation only between the parameters Δχ and δ of the latter alloy that was similar to that of the former alloy.

scholarly journals Microstructures and Isothermal Oxidation of the Alumina Scale Forming Nb1.45Si2.7Ti2.25Al3.25Hf0.35 and Nb1.35Si2.3Ti2.3Al3.7Hf0.35 Alloys

Materials ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 759 ◽  
Author(s):  
Mohammad Ghadyani ◽  
Claire Utton ◽  
Panos Tsakiropoulos
Keyword(s):  
Solid Solution ◽  
Cast Alloy ◽  
Alumina Scale ◽  
Isothermal Oxidation ◽  
Intermetallic Alloys ◽  
High Entropy ◽  
Heat Treated ◽  
Composite Silicide ◽  
Definition Of ◽  
Selection Of

Coating system(s) will be required for Nb-silicide based alloys. Alumina forming alloys that are chemically compatible with the Nb-silicide based alloy substrate could be components of such systems. The intermetallic alloys Nb1.45Si2.7Ti2.25Al3.25Hf0.35 (MG5) and Nb1.35Si2.3Ti2.3Al3.7Hf0.35 (MG6) were studied in the cast, heat treated and isothermally oxidised conditions at 800 and 1200 °C to find out if they are αAl2O3 scale formers. A (Al/Si)alloy versus Nb/(Ti + Hf)alloy map, which can be considered to be a map for Multi-Principle Element or Complex Concentrated Nb-Ti-Si-Al-Hf alloys, and a [Nb/(Ti + Hf)]Nb5Si3 versus [Nb/(Ti + Hf)]alloy map were constructed making use of the alloy design methodology NICE and data from a previously studied alloy, and were used to select the alloys MG5 and MG6 that were expected (i) not to pest, (ii) to form αAl2O3 scale at 1200 °C, (iii) to have no solid solution, (iv) to form only hexagonal Nb5Si3 and (v) to have microstructures consisting of hexagonal Nb5Si3, Ti5Si3, Ti5Si4, TiSi silicides, and tri-aluminides and Al rich TiAl. Both alloys met the requirements (i) to (v). The alumina scale was able to self-heal at 1200 °C. Liquation in the alloy MG6 at 1200 °C was linked with the formation of a eutectic like structure and the TiAl aluminide in the cast alloy. Key to the oxidation of the alloys was the formation (i) of “composite” silicide grains in which the Nb5Si3 core was surrounded by the Ti5Si4 and TiSi silicides, and (ii) of tri-aluminides with high Al/Si ratio, particularly at 1200 °C and very low Nb/Ti ratio forming in-between the “composite” silicide grains. Both alloys met the “standard definition” of high entropy alloys (HEAs). Compared with HEAs with bcc solid solution and intermetallics, the VEC values of both the alloys were outside the range of reported values. The parameters VEC,  and  of Nb-Ti-Si-Al-Hf coating alloys and non-pesting Nb-silicide based alloys were compared and trends were established. Selection of coating alloys with possible “layered” structures was discussed and alloy compositions were proposed.

scholarly journals On the Microstructure and Isothermal Ooxidation of Silica and Alumina Scale Forming Si-23Fe-15Cr-15Ti-1Nb and Si-25Nb-5Al-5Cr-5Ti (at.%) Silicide Alloys

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1091 ◽  
Author(s):  
Ofelia Hernández-Negrete ◽  
Panos Tsakiropoulos
Keyword(s):  
Internal Oxidation ◽  
Eutectic Reaction ◽  
Alumina Scale ◽  
Isothermal Oxidation ◽  
Primary Phase ◽  
Coating System ◽  
Al2o3 Scale ◽  
Binary Eutectic ◽  
Oxidation Resistant ◽  
Α Al2o3

An Nb-silicide based alloy will require some kind of coating system. Alumina and/or SiO2 forming alloys that are chemically compatible with the substrate could be components of such systems. In this work, the microstructures, and isothermal oxidation at 800 °C and 1200 °C of the alloys (at.%) Si-23Fe-15Cr-15Ti-1Nb (OHC1) and Si-25Nb-5Al-5Cr-5Ti (OHC5) were studied. The cast microstructures consisted of the (TM)6Si5, FeSi2Ti and (Fe,Cr)Si (OHC1), and the (Nb,Ti)(Si,Al)2, (Nb,Cr,Ti)6Si5, (Cr,Ti,Nb)(Si,Al)2 (Si)ss and (Al)ss (OHC5) phases. The same compounds were present in OHC1 at 1200 °C and the (Nb,Ti)(Si,Al)2 and (Nb,Cr,Ti)6Si5 in OHC5 at 1400 °C. In OHC1 the (TM)6Si5 was the primary phase, and the FeSi and FeSi2Ti formed a binary eutectic. In OHC5 the (Nb,Ti)(Si,Al)2 was the primary phase. At 800 °C both alloys did not pest. The scale of OHC1 was composed of SiO2, TiO2 and (Cr,Fe)2O3. The OHC5 formed a very thin and adherent scale composed of Al2O3, SiO2 and (Ti(1−x−y),Crx,Nby)O2. The scale on (Cr,Ti,Nb)(Si,Al)2 had an outer layer of SiO2 and Al2O3 and an inner layer of Al2O3. The scale on the (Nb,Cr,Ti)6Si5 was thin, and consisted of (Ti(1−x−y),Crx,Nby)O2 and SiO2 and some Al2O3 near the edges. In (Nb,Ti)(Si,Al)2 the critical Al concentration for the formation of Al2O3 scale was 3 at.%. For Al < 3 at.% there was internal oxidation. At 1200 °C the scale of OHC1 was composed of a SiO2 inner layer and outer layers of Cr2O3 and TiO2, and there was internal oxidation. It is most likely that a eutectic reaction had occurred in the scale. The scale of OHC5 was α-Al2O3. Both alloys exhibited good correlations with alumina forming Nb-Ti-Si-Al-Hf alloys and with non-pesting and oxidation resistant B containing Nb-silicide based alloys in maps of the parameters δ, Δχ and VEC.

Preparation of a Light-Weight MgCaAlLiCu High-Entropy Alloy

2017 ◽  
Vol 727 ◽  
pp. 132-135 ◽  
Author(s):  
Xing Hao Du ◽  
Rui Wang ◽  
Cai Chen ◽  
Bao Lin Wu ◽  
J.C. Huang
Keyword(s):  
Solid Solution ◽  
Tetragonal Symmetry ◽  
High Entropy Alloy ◽  
Solid Solution Phase ◽  
Light Weight ◽  
High Fracture ◽  
Compression Process ◽  
High Entropy ◽  
Symmetry Structure ◽  
Alloy Cast

In this paper, a light-weight equimolar MgCaAlLiCu high entropy alloy (HEA) is reported. The microstructure of the alloy cast in copper mould was composed mainly of a solid solution phase with tetragonal symmetry structure, presenting the high-entropy alloy nature. The alloy exhibited high fracture strength of 910 MPa during the room-temperature compression process. Based on thermodynamic calculation, the underlying reason for the formation of the solid solution in the MgCaAlLiCu alloy is given.

scholarly journals A facile synthesis of high entropy alloy nanoparticle–activated carbon nanocomposites for synergetic degradation of methylene blue

RSC Advances ◽  
2021 ◽  
Vol 11 (40) ◽  
pp. 24636-24646
Author(s):  
Yuyu Liu ◽  
Zheng Chen ◽  
Xiaoqin Yang ◽  
Jinyong Zhang ◽  
Zhonggang Sun ◽  
...  
Keyword(s):  
Solid Solution ◽  
Methylene Blue ◽  
Catalytic Performance ◽  
Solution Phase ◽  
High Entropy Alloy ◽  
Solid Solution Phase ◽  
Facile Synthesis ◽  
Carbon Nanocomposites ◽  
High Entropy ◽  
Time Required

CoCrFeMnNi HEA NPs–AC were synthesized facilely with FCC solid solution phase and outstanding catalytic performance. The time required to reduce MB concentration can be as short as 12 min with the kobs of 0.191 min−1 for the 10 wt% catalyst.

Non-equiatomic W10Mo27Cr21Ti22Al20 high-entropy alloy produced by mechanical alloying and spark plasma sintering: Phase evolution and mechanical properties

2022 ◽  
pp. 146442072110510
Author(s):  
Hamed Naser-Zoshki ◽  
Ali-Reza Kiani-Rashid ◽  
Jalil Vahdati-Khaki
Keyword(s):  
Mechanical Properties ◽  
Solid Solution ◽  
Mechanical Alloying ◽  
Spark Plasma Sintering ◽  
Elevated Temperatures ◽  
High Entropy Alloy ◽  
Solid Solution Phase ◽  
High Entropy ◽  
Plasma Sintering ◽  
Spark Plasma

In this work, non-equiatomic W10Mo27Cr21Ti22Al20 refractory high-entropy alloy (RHEA) was produced using mechanical alloying followed by spark plasma sintering. The phase formation, microstructure, and compressive mechanical properties of the alloy were studied. During mechanical alloying, a Body-centered cubic (BCC) solid solution phase with a particle size of less than 1 µm was obtained after 18 h ball milling. The microstructure of the sintered sample exhibits three distinct phases consisting of two solid solution phases BCC1 and BCC2 as well as fine TiCxOy precipitates distributed in them. The volume fractions of each phase were about 79%, 8%, and 13%, respectively. The sintered W10Mo27Cr21Ti22Al20 showed yield strengths of 2465, 1506, 405, and 290 MPa at room temperature 600, 1000, and 1200°C, respectively, which are about twice that of the same refractory high-entropy alloy produced by vacuum arc melting. At 1000 and 1200°C, the strength after yielding gradually increased to 970 and 718 MPa at a compressive strain of 60%. The studied refractory high-entropy alloy can have good potential in high-temperature applications due to its high specific strength at elevated temperatures compared to conventional Ni-based superalloys and most as-reported refractory high-entropy alloys.

scholarly journals Thermal Stability of MoNbTaVW High Entropy Alloy Thin Films

Coatings ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 941
Author(s):  
Ao Xia ◽  
Robert Franz
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Thermal Stability ◽  
Solid Solution ◽  
Electrical Conductivity ◽  
High Entropy Alloy ◽  
Solid Solution Phase ◽  
Body Centered Cubic ◽  
High Entropy ◽  
Thermal Stability Of

Refractory high entropy alloys are an interesting material class because of their high thermal stability, decent electrical conductivity, and promising mechanical properties at elevated temperature. In the present work, we report on the thermal stability of body-centered cubic MoNbTaVW solid solution thin films that were synthesized by cathodic arc deposition. After vacuum annealing up to 1600 °C, the morphology, chemical composition, crystal structure, and electrical conductivity, as well as the mechanical properties, were analyzed. The observed body-centered cubic MoNbTaVW solid solution phase is stable up to 1500 °C. The evolution of electrical and mechanical properties due to the annealing treatment is discussed based on the observed structural changes of the synthesized thin films.

Elemental effect on formation of solid solution phase in CoCrFeNiX and CoCuFeNiX (X = Ti, Zn, Si,Al) high entropy alloys

2019 ◽  
Vol 35 (14) ◽  
pp. 1700-1707
Author(s):  
Jil Joy ◽  
Mahesh Jadhav ◽  
Disna Sahane ◽  
Deepak Davis ◽  
Sheela Singh
Keyword(s):  
Solid Solution ◽  
Solution Phase ◽  
Solid Solution Phase ◽  
High Entropy Alloys ◽  
High Entropy

Carbothermal shock synthesis of high-entropy-alloy nanoparticles

Science ◽  
2018 ◽  
Vol 359 (6383) ◽  
pp. 1489-1494 ◽  
Author(s):  
Yonggang Yao ◽  
Zhennan Huang ◽  
Pengfei Xie ◽  
Steven D. Lacey ◽  
Rohit Jiji Jacob ◽  
...  
Keyword(s):  
Solid Solution ◽  
Ammonia Oxidation ◽  
Metal Salt ◽  
Shock Duration ◽  
High Entropy Alloy ◽  
Solid Solution Phase ◽  
Alloy Nanoparticles ◽  
Carbon Supports ◽  
High Entropy ◽  
Wide Range

The controllable incorporation of multiple immiscible elements into a single nanoparticle merits untold scientific and technological potential, yet remains a challenge using conventional synthetic techniques. We present a general route for alloying up to eight dissimilar elements into single-phase solid-solution nanoparticles, referred to as high-entropy-alloy nanoparticles (HEA-NPs), by thermally shocking precursor metal salt mixtures loaded onto carbon supports [temperature ~2000 kelvin (K), 55-millisecond duration, rate of ~105 K per second]. We synthesized a wide range of multicomponent nanoparticles with a desired chemistry (composition), size, and phase (solid solution, phase-separated) by controlling the carbothermal shock (CTS) parameters (substrate, temperature, shock duration, and heating/cooling rate). To prove utility, we synthesized quinary HEA-NPs as ammonia oxidation catalysts with ~100% conversion and >99% nitrogen oxide selectivity over prolonged operations.

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