THE EFFECT OF BORON CONTENT ON THE STRUCTURE AND MECHANICAL PROPERTIES OF ELECTRON-BEAM HIGH-ENTROPY AlNiCoFeCrTiBх COATINGS

S.O. Nakonechnyi*,
 
A.I. Yurkova,
 
P.I. Loboda,
 
Lan Jinlong
 

National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, 37, Prosp. Beresteiskyi, Kiev, 03056, Ukraine
sergeynuts@gmail.com
Powder Metallurgy - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2023, #05/06
http://www.materials.kiev.ua/article/3597

Abstract

High–entropy coatings produced by electron-beam deposition of multicomponent Al–Ni–Cо–Fe–Cr–Ti–Bx (х = 0, 0.25, 0.5, and 1 mol) powder mixtures onto steel substrates in vacuum were examined. The effect of boron content on the phase composition, structure, and strength properties of the AlNiCoFeCrTiBx coatings was studied employing X-ray diffraction, microstructural analysis, and micromechanical tests. The AlNiCoFeCrTi and AlNiCoFeCrTiB0.25 coatings showed a typical dendritic and interdendritic structure and consisted of two substitutional solid solutions with a body-centered cubic (bcc) structure, differing in lattice parameters. An increase in the boron content to 0.5 mol changed the phase composition and led to the formation of in-situ titanium diboride TiB2 as fine inclusions and chromium boride Cr2B as elongated inclusions in the coatings besides the two bcc solid solutions (bcc1 and bcc2). When 1 mol of boron was added, the coatings remained four-phase, while the amount and sizes of TiB2 Cr2B inclusions increased. Moreover, with 1 mol of boron, the ratio between the bcc1 and bcc2 phases increased toward bcc2 because of the removal of Cr and Ti atoms. Mechanical tests showed that the microhardness and yield stress of the AlNiCoFeCrTiBx coatings produced by electron-beam deposition increased by 1.6 times when boron content raised to 1 mol: from 8.8 and 2.4 GPa for the AlNiCoFeCrTi coatings to 14.2 and 4 GPa for the AlNiCoFeCrTiB coatings. The significant enhancement in the strength characteristics (hardness and yield stress) of high-entropy coatings with greater boron content can be attributed to the solid-solution hardening effect of interstitial boron atoms and to the strengthening effect of boride phase inclusions.


BORON, CHROMIUM BORIDE, COATINGS, ELECTRON-BEAM DEPOSITION, HIGH-ENTROPY ALLOY, MECHANICAL PROPERTIES, PHASE COMPOSITION, STRUCTURE, TITANIUM DIBORIDE