THE STRUCTURE FORMATION AND HARDNESS OF COATINGS OF HIGH-ENTROPY ALLOYS OBTAINED BY ELECTROSPARK ALLOYING

Abstract

In this paper, the features of using high-entropy alloys (HEAs) as coating materials are considered. It is shown that electrospark alloying (ESA) allows creating high-quality coatings with a high operational life. For the study, AlCrFeCoNiCu_х cast alloys (x = 0; 2 mol) were used, which were obtained by the method of arc melting. Using ESA method on the Elitron-52A device, coatings were obtained from HEAs on steel 45. The phase composition, hardness and microstructure of cast alloys are compared with coatings based on them. It was shown that the initial state HEAs has an inhomogeneous structure characteristic of a cast alloy, crystallizes in the form of simple solid solutions based on phases with BCC and FCC structures, the AlCrFeCoNi alloy has a higher hardness (6229 MPa) in comparison with the AlCrFeCoNiCu₂ alloy (5814 GPa). Studies of the structural-phase state of samples showed that they consist of a coating, a transition zone, and a substrate with a ferrite-pearlite structure. An increase in the discharge energy W_р during the ESA contributes to an increase in the hardness, thickness, and continuity of the coatings. At W_p = 0.13 J, the thickness of the coatings is 20 μm, the continuity is 70%, with W_p = 4.6 J — up to 130 μm, the continuity is 100%. Аs opposed to cast alloys, high-entropy coatings have a high microhardness; at a discharge energy of 4.6 J, it is 6230 and 7320 MPa, respectively, for AlCrFeCoNiCu₂ and AlCrFeCoNi. The addition of copper in the electrode material increases the thickness of the coatings. It is shown that both solid alloys and coatings form simple solid solutions typical of high-entropy alloys. In contrast to the cast alloys, the coating characteristic homogeneous microstructure.