CC BY
52iSHS 2019
Moscow, Russia
CENTRIFUGAL ASSISTED SHS SURFACING OF CoCrFeNiMnAlx HIGH
ENTROPY ALLOY ON Ti ALLOY SUBSTRATE
V. N. Sanin*", D. M. Ikornikov", O. A. Golosova", D. E. Andreev", and V. I. Yukhvid"
aMerzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of
Sciences, Chernogolovka, Moscow, 142432 Russia
*e-mail: svn@ism.ac.ru
DOI: 10.24411/9999-0014A-2019-10144
High-entropy alloys (HEAs) are newly developed multicomponent alloys wherein the configurational entropy (CE) is higher than the fusion entropy of most common metals [1]. These alloys draw increasing scientific interest, especially regarding the fundamental aspects of massive solid-solution (SS) phases and the basic role of CE therein [2-5]. These efforts are well motivated, as the HEA concept was originally based on CE maximization (i.e., by increasing the number of equiatomically proportioned alloying elements). However, this strategy has led so far to only a few successful single-phase alloys [6-9] and the role of CE in these successful cases is being debated. Instead, most of the investigated alloys pertaining to this class develop complex, multiphase microstructures and low tensile ductility, providing limited prospects for future applications. Even for the present success stories such as Co20Cr20Fe20Mn20Ni20, the most promising HEA with a highly stable and ductile single-phase SS, the specific composition tolerance window, the weak high-temperature behavior, and the expensive alloying (e.g., Ni) are still pending challenges. Considering that the overall applicability of a new material class is strongly linked to the versatility of the properties it can deliver in exchange for the practical and economical complexities created by its bulk processing, the above-mentioned difficulties and uncertainties call for a critical assessment of the versatility versus complexity balance in HEA.
The main aim of this work is to provide such an analysis as well as new perspectives to improve on the aforementioned limiting aspects of apply properties. Thus, in what follows, taking the reported Co20Cr20Fe20Mn20Ni20 alloy as the starting point, we investigate the possibility of forming the coating in-situ SHS (SHS-surfacing) of HEAs Co20Cr20Fe20Mn20Ni20) on a metal substrate (Ti alloy).
The compositional design, centrifugal casting (SHS processing routes), and microstructure/property relations of synthesized HEA/Ti substrate composite will pointed out. The HEA surfacing on Ti alloy substrate was carried out by a relatively new method called the SHS surfacing, which is one of the technological directions of metallothermic SHS (SHS metallurgy) [10]. This is a low-energy consuming technique due to the use of internal energy released in high-caloric combustion reactions. Recently, cast high-entropy transition metal alloys were first prepared [11]. The use of highly exothermic SHS compounds of the thermite type makes it possible to produce melts of combustion products (at temperature above 2500°C) and, as a consequence, to obtain cast products (ingots). Cast coatings can be formed directly during synthesis process (in-situ SHS) on a metal plate (substrate) placed in the bottom part of refractory mold (Fig. 1).
However, the surfacing on substrates consisting of active metals will inevitably lead to the formation of not only a mechanical connection between the layers but also the formation of new structural components based on active metal and alloy components. That is why in the frame of this work special attention was paid to the study of the area of section of the formed layer material consisting of titanium alloy VT20 (Russian trademark) and cast HEA.
XV International Symposium on Self-Propagating High-Temperature Synthesis
Fig. 1. (a) Schema of initial sample and (b) outward appearance of sample after SHS surfacing (cross cutting).
Figure 2 and 3 shows the structure of transition zone between deposited coating layer and Ti substrate. Analysis of the microstructure of the deposited layer (Figs. 2a, 2b) revealed three zones where the base material (Ti) gradient distributed over the height of the deposited layer. Figure 2c shows that the hardness of coating is higher by 3 times than that of substrate.
M
Spectrum Al Ti Cr Mn Fe Co Ni
1 1.1 98.9
2 8.3 55.5 7.2 4.7 8.1 8.6 7.6
3 13.7 24.4 11.9 7.9 13.7 14.9 13.5
(b)
(c)
Fig. 2. (a) SEM image of coating/Ti substrate composite, (b) EDS data of transition zone, and (c) dependence of microhardness on height of coating.
Fig. 3. EDX maps of boundary layer of the SHS coating.
The analysis of the obtained data allows drawing a conclusion about the prospects of the materials under investigation and the method of their production for the formation of volumetric
■SHS 2019 Moscow, Russia
materials and coating of them. The production of metallic composite materials based on the
new principle of formation of polymetallic alloys can significantly expand the basis for the
creation of new materials and facilitate the creation of new technological models.
The research was supported by the Russian Foundation for Basic Research, (project
no. 19-08-01108).
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