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65XV International Symposium on Self-Propagating High-Temperature Synthesis
SHS OF AlxCoCrFeNi HIGH-ENTROPY ALLOYS F. Kaya" and B. Derm*"
aIstanbul Technical University, Metallurgical and Materials Engineering Department, Maslak, Istanbul, 34469 Turkey *e-mail: [email protected]
DOI: 10.24411/9999-0014A-2019-10057
High-entropy alloys (HEAs) are new advanced materials group with properties that can meet the demands of the contemporary engineering disciplines. HEAs are simply defined as solid solution alloys containing more than four principal elements in equal or near-equal molar proportions and each principal element having a molar concentration between 5 and 35 at % [1, 2]. AlxCoCrFeNi system is one of the mostly studied HEAs which has excellent mechanical and chemical properties such as hardness, corrosion resistance, compressive strength, and abrasion resistance at both low and high temperatures [1-5]. AlxCoCrFeNi alloys could be potentially used for many application areas such as jet/turbine engine components, gear parts and hard facing applications; piping, pumps, mixing equipment for excessive corrosive chemical plants sea-based maritime structures as well as catalysts applications [1, 2, 6, 7].
AlxCoCrFeNi HEAs are usually produced by two different production methods: arc melting and mechanical alloying which are laboratory scale production methods rather than a mass production method and performed by using expensive metallic raw materials in a very long process time [1, 2]. In order for HEAs to replace the contemporary engineering materials, they are needed to be produced by cheaper, faster and easier techniques such as SHS method.
In the present paper, AlxCoCrFeNi alloys were produced by aluminothermic type synthesis method from their oxides (i.e. Co3O4, &2O3, NiO, Fe2O3). Prior to the experiments, some thermochemical modelling studies were done to estimate the required amounts of the input materials, the adiabatic temperature of the SHS reactions, as well as the phase diagrams of HEAs by FactSage™ (Fig. 1).
0.35
0.30
0.2s 0.20 0.1S 0.10 0.0s
' - _ SLAG
Ni(Liquid alloy) ^^
Cfl(Uqttid"aII5y) ^—— — Fe(Llquld alloy)
^^^ GAS
:__^.........
19 20 21 22 23 24 25 26 27 28 29 30
AI addition, g
(a) (b)
Fig. 1. Thermochemical calculations of a SHS thermite type reaction for (a) the product change and (b) the adiabatic temperature change by Al addition.
After thermochemical modelling, the oxide materials and reductant Al were dried and mixed for 60 min. After realizing the SHS experiments in Cu crucibles, the samples were remelted in a vacuum arc melter for homogenizing and rod casting (Fig. 2a). X-ray diffraction analysis
ÏSHS2019
Moscow, Russia
(XRD) was carried out using CuXa radiation in order to determine the crystalline phases (Fig. 2b). It was seen that the sample was crystalline, having (110), (200), and (211) diffraction peaks of a BCC phase. Therefore, it was concluded that the as-received sample was a BCC solid solution, which was in accordance with literature findings.
(a)
* BCC
o O _I_L
40 50 60
[2Theta]
(b)
Fig. 2. (a) Rod casted sample of AlCoCrFeNi HEA, (b) XRD spectrum of the sample.
XRD results were also compared with thermochemical calculations. Table 1 shows that one selected composition scenario by model calculations agreed with experimental result and thus, an equimolar AlCoCrFeNi HEA was produced successfully.
Table 1. Chemical analysis of the sample.
Al Co Cr Fe Ni
FactSageTM (mol %) 20.86 19.52 20.36 19.47 19.77
FactSage™ (wt %) 11 22 21 21 23
XRD (wt %) 11.70 23.05 21.04 21.38 22.80
The research was supported by the Scientific and Technological Research Council of Turkey
(TUBITAK, project no. 119M086).
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