Nanocomposites and nanomaterials

Nanostructured AlCoFeCrVNi and AlCoFeCrVTi  high-entropy alloys resulted from mechanical alloying and sintering
Yurkova A.I., Chernyavsky V.V., Kushnir V.V. 
High-Temperature Materials and Powder MetallurgyDepartment, Igor Sikorsky Kyiv Polytechnic Institute,
Prospect Peremogy, 37, Kyiv-03056, Ukraine. 
E-mail: vadikv13@gmail.com 

This study reports the structural evolution of AlCoFeCrVNi and AlCoFeCrVTi high-entropy alloys [1] from elemental materials to solid solution phases during mechanical alloying (MA) [2, 3], and further, to equilibrium phases during high pressure sintering [3]. 
The phase and structural transformations in equiatomic powder compositions of the Al-Co-Fe-Cr-V-Ni(Ti) systems during mechanical alloying (MA) and subsequent sintering under high pressure 5 GPa were studied by X-ray diffraction analysis and scanning electron microscopy. It was established that the nanocrystalline AlCoFeCrVNi(Ti) synthesized by MA consists of a metastable supersaturated bcc and fcc solid solutions. It has been shown that the alloying process between different alloy components begins with the crystallites refinement to nanosizes and occurs heterogeneously due to different melting points of the components, and therefore to different binding energies between atoms and their different diffusion activity [1, 2]. High pressure sintering at a relatively low temperature 800 C was found to contribute to the maintenance of the nanostructured state and phase composition in compact specimens of AlCoFeCrVNi(Ti) alloys obtained during MA. In both alloys metastable solid solutions during sintering transform into more stable ones with the increasing of fcc solid solution content compared to the bcc one.

1.	Murty B.S., Yeh J-W., Ranganathan S., Bhattacharjee P.P. High-Entropy Alloys, 2nd Edition. Elsevie, 2019,  388 p. 
2.	Yurkova O.I., Cherniavsky V.V., V. Bolbut, and et. al. Structure formation and mechanical properties of the high-entropy AlCuNiFeCr alloy prepared by mechanical alloying and spark plasma sintering // J. Alloys and Compounds.-2019.-786.-P. 139-148.
3.	Yurkova A.I., Chernyavskii V.V.,  Gorban V.F. Structure and Mechanical Properties of High-Entropy AlCuNiFeTi and AlCuNiFeCr Alloys Produced by Mechanical Activation Followed by Pressure Sintering // Powder Metallurgy and Metal Ceramics..  2016.-55, Issue 3.-P. 152–163.