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Centrifugal Metallothermic SHS of Cast Co–Cr–Fe–Ni–Mn–(Х) Alloys (2)

Release time: 2021-04-09 11:11:11  Hits: 24

The most widely studied HEAs are Co–Cr–Fe– Ni–Mn systems. These equiatomic alloys are represented by a disordered fcc solid-solution structure [3], which makes them attractive for research. It is common knowledge also that the fcc structure is thermodynamically stable at temperatures of more than 900°C [25]. In general, the single-phase structure of this alloy is stable and, therefore, it is widely used as a “model” HEA. It should be noted that the CoCrFeNiMn alloy exhibits high mechanical properties-sufficiently high plasticity at room temperatures and an elongation to failure of 70–80% [25]-which is the second reason for research interest [25‒28].

 

However, the widespread implementation of CoCrFeNiMn alloys requires carrying out studies aimed at revealing the regularities of structure formation. Obviously, an optimal set of properties of HEAs is achieved by the required structure consisting of, for example, plastic solid-solution matrix and dispersion precipitates of strengthening phase. Nowadays, HEAs are widely studied; however, the regularities of effect of the content of alloying elements and the heat treatment on the structure and properties of these alloys are as of yet imperfectly understood and come to a focus of primary tasks. There is an urgent need for additional studies aimed at creating new metal materials based on complex alloyed HEAs, as well as developing effective technologies for their production with a given composition and a set of structural elements.

 

In this regard, studies on improving the strength of HEAs [28, 29] while reducing their specific weight, owing to the careful selection of components and their concentrations [19, 20], seem to be promising. Furthermore, the density of HEAs can be reduced by an economical alloying with light elements such as Al, Ti, Si, B, etc. The complex of alloying components that was introduced can significantly increase the strength, oxidation resistance, and creep resistance. Possible strengthening mechanisms in these alloys and methods for their controlling by quantitative variations of chemical composition remain poorly investigated due to the large amount of possible combinations. It can be argued that the whole range of such materials based on HEAs and their properties are not fully studied. Therefore, the development of new structurally strengthened materials based on HEAs is of great interest, making it possible to expand the possible applications of HEAs at elevated temperatures.

 

For the most part, the studies of HEAs are focused on defining the relationship between the microstructure and the measured properties. Significantly less attention is being given to studying and developing new effective methods for creating HEAs. The presence of a long list of components in the alloy makes the process of acquisition a difficult scientific and technological task. The most important technological factor of obtaining polymetallic high-entropy alloys is providing a high degree of homogenization of chemical composition. It is also essential to provide a sufficiently high cooling rate of alloy in liquid and solid states in order to suppress diffusion processes leading to the uncontrolled formation of chemical compounds.

 

The aim of this work is to study the possibilities of preparing CoCrFeNiMn–(Х) HEAs by the centrifugal metallothermic SHS method [30–32], as well as to test chemical and technological modes for modifying alloys during synthesis (in situ) by introducing the alloying components into the starting exothermic mixtures.


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