Solidification microstructures of multielement carbides in the high entropy Zr-Nb-Hf-Ta-Cx system produced by arc melting

The solidification microstructures of the TiNbTaZr medium-entropy alloy and TiNbTaZrX (X = V, Mo, and W) high-entropy alloys (HEAs), including the TiNbTaZrMo bio-HEA, were investigated. Equiaxed dendrite structures were observed in the ingots that were prepared by arc melting, regardless of the position of the ingots and the alloy system. In addition, no significant difference in the solidification microstructure was observed in TiZrNbTaMo bio-HEAs between the arc-melted (AM) ingots and cold crucible levitation melted (CCLM) ingots. A cold shut was observed in the AM ingots, but not in the CCLM ingots. The interdendrite regions tended to be enriched in Ti and Zr in the TiNbTaZr MEA and TiNbTaZrX (X = V, Mo, and W) HEAs. The distribution coefficients during solidification, which were estimated by thermodynamic calculations, could explain the distribution of the constituent elements in the dendrite and interdendrite regions. The thermodynamic calculations indicated that an increase in the concentration of the low melting-temperature V (2183 K) leads to a monotonic decrease in the liquidus temperature (TL), and that increases in the concentration of high melting-temperature Mo (2896 K) and W (3695 K) lead to a monotonic increase in TL in TiNbTaZrXx (X = V, Mo, and W) (x = 0 − 2) HEAs.

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Microstructure and Mechanical Properties of VTaTiMoAlx Refractory High Entropy Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.898.638 ◽

2017 ◽

Vol 898 ◽

pp. 638-642 ◽

Cited By ~ 7

Author(s):

Dong Xu Qiao ◽

Hui Jiang ◽

Xiao Xue Chang ◽

Yi Ping Lu ◽

Ting Ju Li

Keyword(s):

Mechanical Properties ◽

Vacuum Arc ◽

High Entropy Alloys ◽

X Ray Diffraction ◽

Dendrite Structure ◽

X Ray ◽

High Entropy ◽

Arc Melting ◽

Vacuum Arc Melting ◽

Microstructure And Mechanical Properties

A series of refractory high-entropy alloys VTaTiMoAlx with x=0,0.2,0.6,1.0 were designed and produced by vacuum arc melting. The effect of added Al elements on the microstructure and mechanical properties of refractory high-entropy alloys were investigated. The X-ray diffraction results showed that all the high-entropy alloys consist of simple BCC solid solution. SEM indicated that the microstructure of VTaTiMoAlx changes from equiaxial dendritic-like structure to typical dendrite structure with the addition of Al element. The composition of different regions in the alloys are obtained by energy dispersive spectroscopy and shows that Ta, Mo elements are enriched in the dendrite areas, and Al, Ti, V are enriched in inter-dendrite areas. The yield strength and compress strain reach maximum (σ0.2=1221MPa, ε=9.91%) at x=0, and decrease with the addition of Al element at room temperature. Vickers hardness of the alloys improves as the Al addition.

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Microstructure and Mechanical Properties of Sintered and Heat-Treated HfNbTaTiZr High Entropy Alloy

Metals ◽

10.3390/met9121324 ◽

2019 ◽

Vol 9 (12) ◽

pp. 1324 ◽

Cited By ~ 4

Author(s):

Jaroslav Málek ◽

Jiří Zýka ◽

František Lukáč ◽

Jakub Čížek ◽

Lenka Kunčická ◽

...

Keyword(s):

Powder Metallurgy ◽

Dendritic Structure ◽

Cold Isostatic Pressing ◽

High Entropy Alloy ◽

High Entropy ◽

Arc Melting ◽

Powder Metallurgy Process ◽

Heat Treated ◽

Near Net Shape ◽

Metallurgy Process

High entropy alloys (HEAs) have attracted researchers’ interest in recent years. The aim of this work was to prepare the HfNbTaTiZr high entropy alloy via the powder metallurgy process and characterize its properties. The powder metallurgy process is a prospective solution for the synthesis of various alloys and has several advantages over arc melting (e.g., no dendritic structure, near net-shape, etc.). Cold isostatic pressing of blended elemental powders and subsequent sintering at 1400 °C for various time periods up to 64 h was used. Certain residual porosity, as well as bcc2 (Nb- and Ta-rich) and hcp (Zr- and Hf-rich) phases, remained in the bcc microstructure after sintering. The bcc2 phase was completely eliminated during annealing (1200 °C/1h) and subsequent water quenching. The hardness values of the sintered specimens ranged from 300 to 400 HV10. The grain coarsening during sintering was significantly limited and the maximum average grain diameter after 64 h of sintering was approximately 60 μm. The compression strength at 800 °C was 370 MPa and decreased to 47 MPa at 1200 °C. Porosity can be removed during the hot deformation process, leading to an increase in hardness to ~450 HV10.

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Synthesis of Spherical V-Nb-Mo-Ta-W High-Entropy Alloy Powder Using Hydrogen Embrittlement and Spheroidization by Thermal Plasma

Metals ◽

10.3390/met9121296 ◽

2019 ◽

Vol 9 (12) ◽

pp. 1296 ◽

Cited By ~ 7

Author(s):

Won-Hyuk Lee ◽

Ki Beom Park ◽

Kyung-Woo Yi ◽

Sung Yong Lee ◽

Kwangsuk Park ◽

...

Keyword(s):

Hydrogen Embrittlement ◽

Thermal Plasma ◽

Fine Powder ◽

Hydrogen Atmosphere ◽

Vacuum Arc ◽

Cubic Phase ◽

High Entropy Alloy ◽

High Entropy ◽

Inductively Coupled ◽

Arc Melting

V-Nb-Mo-Ta-W high-entropy alloy (HEA), one of the refractory HEAs, is considered as a next-generation structural material for ultra-high temperature uses. Refractory HEAs have low castability and machinability due to their high melting temperature and low thermal conductivity. Thus, powder metallurgy becomes a promising method for fabricating components with refractory HEAs. Therefore, in this study, we fabricated spherical V-Nb-Mo-Ta-W HEA powder using hydrogen embrittlement and spheroidization by thermal plasma. The HEA ingot was prepared by vacuum arc melting and revealed to have a single body-centered cubic phase. Hydrogen embrittlement which could be achieved by annealing in a hydrogen atmosphere was introduced to get the ingot pulverized easily to a fine powder having an angular shape. Then, the powder was annealed in a vacuum atmosphere to eliminate the hydrogen from the hydrogenated HEA, resulting in a decrease in the hydrogen concentration from 0.1033 wt% to 0.0003 wt%. The angular shape of the HEA powder was turned into a spherical one by inductively-coupled thermal plasma, allowing to fabricate spherical V-Nb-Mo-Ta-W HEA powder with a d50 value of 28.0 μm.

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Microstructure and Mechanical Properties of Co-Cr-Mo-Si-Y-Zr High Entropy Alloy

Metals ◽

10.3390/met10111456 ◽

2020 ◽

Vol 10 (11) ◽

pp. 1456

Author(s):

Karsten Glowka ◽

Maciej Zubko ◽

Paweł Świec ◽

Krystian Prusik ◽

Robert Albrecht ◽

...

Keyword(s):

Electron Microscopy ◽

Microstructure Analysis ◽

Vacuum Arc ◽

High Entropy Alloy ◽

High Entropy ◽

Arc Melting ◽

Vacuum Arc Melting ◽

Transmission Electron ◽

Multi Phase ◽

Principal Elements

Presented work was focused on obtaining new, up to our knowledge, non-described previously in the literature high entropy Co15Cr15Mo25Si15Y15Zr15 alloy to fill in the knowledge gap about the six-elemental alloys located in the adjacent to the center of phase diagrams. Material was obtained using vacuum arc melting. Phase analysis revealed the presence of a multi-phase structure. Scanning electron microscopy microstructure analysis revealed the existence of three different phases with partially dendritic structures. Chemical analysis showed that all phases consist of all six principal elements—however, with different proportions. Transmission electron microscopy microstructure analysis confirmed the presence of amorphous and nanocrystalline areas, as well as their mixture. For the studied alloy, any phase transformation and solid-state crystallization were not revealed in the temperature range from room temperature up to 1350 °C. Nanoindentation measurements revealed high nanohardness (13(2) GPa and 18(1) GPa for dendritic and interdendritic regions, respectively) and relatively low Young’s modulus (185(23) GPa and 194(9) GPa for dendritic and interdendritic regions, respectively) of the observed phases.

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Precipitation Hardenable High Entropy Alloy for Tooling Applications

MRS Advances ◽

10.1557/adv.2019.146 ◽

2019 ◽

Vol 4 (25-26) ◽

pp. 1427-1433

Author(s):

O. Stryzhyboroda ◽

U. Hecht ◽

V. T. Witusiewicz ◽

G. Laplanche ◽

A. Asabre ◽

...

Keyword(s):

Precipitation Hardening ◽

High Entropy Alloy ◽

Instrumented Indentation ◽

Cast State ◽

Alloy Development ◽

High Entropy ◽

Arc Melting ◽

Thermodynamic Computations ◽

Thermocalc Software ◽

Cast Microstructure

ABSTRACTWe present a high entropy alloy (HEA) from the system Al-Co-Cr-Fe-Ni with small additions of W, Mo, Si and C which was designed to allow for precipitation hardening by annealing in the temperature range from 600 to 900 °C. The alloy development was supported by thermodynamic computations using ThermoCalc software and the specimens were produced by arc melting. The microstructure of one selected sample in as-cast and annealed conditions was analysed using SEM/EDS, SEM/EBSD and TEM. The as-cast microstructure consists of spinodally decomposed BCC dendrites enveloped by FCC+Cr23C6 eutectic. Upon annealing at 700 °C for 24 h nanoscale precipitates form within the spinodal BCC as well as from FCC. Precipitation is exquisitely uniform leading to an increase in microhardness from 415 HV0.5 in the as-cast state to 560 HV0.5 after annealing. We investigated coarsening of this microstructure using varying holding time for a constant temperature of 700 °C. The microstructure evolution during coarsening and the corresponding mechanical properties obtained from instrumented indentation experiments are presented in this work.

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Microstructure and mechanical properties of RexNbMoTaW high-entropy alloys prepared by arc melting using metal powders

Journal of Alloys and Compounds ◽

10.1016/j.jallcom.2020.154301 ◽

2020 ◽

Vol 827 ◽

pp. 154301 ◽

Cited By ~ 6

Author(s):

Jian Zhang ◽

Yeyuan Hu ◽

Qinqin Wei ◽

Yuan Xiao ◽

Pingan Chen ◽

...

Keyword(s):

Mechanical Properties ◽

High Entropy Alloys ◽

Metal Powders ◽

High Entropy ◽

Arc Melting ◽

Microstructure And Mechanical Properties

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Mechanical Behavior of Novel Suction Cast Ti-Cu-Fe-Co-Ni High Entropy Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.790-791.503 ◽

2014 ◽

Vol 790-791 ◽

pp. 503-508 ◽

Cited By ~ 22

Author(s):

Sumanta Samal ◽

Sutanuka Mohanty ◽

Ajit Kumar Misra ◽

Krishanu Biswas ◽

B. Govind

Keyword(s):

Mechanical Properties ◽

Vacuum Arc ◽

High Entropy Alloys ◽

The Novel ◽

Electron Microscopic ◽

High Entropy ◽

Alloy Chemistry ◽

Arc Melting ◽

Vacuum Arc Melting ◽

Ductile Mode

The present investigation reports mechanical properties of novel multicomponent TixCuyFe20Co20Ni20 high entropy alloys (HEAs) with different alloy chemistry (x/y = 1/3, 3/7, 3/5, 9/11, 1, 11/9 and 3/2). The alloy cylinders were prepared by vacuum arc melting-cum-suction casting route. The detailed electron microscopic observations reveal the presence of three different solid solution phases; FCC (a1) phase, FCC (a2) phase and BCC (b) phase for all the investigated alloys, whereas ultrafine eutectic between FCC (a1) phase, and Ti2 (Co, Ni) - type Laves phase has been observed for the HEAs with x/y = 9/11, 1, 11/9 and 3/2. Room temperature compression test of the suction cast cylinders with aspect ratio of 2/1 has been conducted to obtain mechanical properties of the HEAs. The optimum combination of strength (~ 1.88 GPa) and plasticity (~ 21 %) is obtained for x/y = 9/11; indicating simultaneous improvement of strength as well as plasticity of the novel HEAs. Fractographic analysis of the fractured surfaces reveals mixed mode of fracture for x/y = 1/3, 3/7 and 3/5, ductile mode for x/y = 9/11 and 1, whereas brittle mode of fracture for x/y = 11/9 and 3/2.

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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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