This study reports the structural evolution of multicomponent AlNiCoFeCrTi high-entropy alloy from elemental materials to nanocrystalline metastable solid solution during mechanical alloying (MA), and further, to equilibrium phases during subsequent thermal annealing. It was justified experimentally that shot-time mechanical milling of Al-Ni-Co-Fe-Cr-Ti powder mixture during 3 hours resulted in a single-phase nanocrystalline high-entropy alloy (HEA) with a structure of bcc solid solution. During thermal annealing of the bcc solid solution phase transformation take place, and grain growth of equilibrium phases occur. The phase composition of as-MA alloy transforms to fcc and bcc solid solutions with TiC precipitations' when the MA powder was annealed at 1200 °C for 1 h. X-ray diffraction and electron microscopy data show that the nanocrystalline powder microstructure is retained in the alloy with no grain growth. The AlNiCoFeCrTi HEA exhibit 7.1 GPa and 9.2±0.3 GPa in Vickers hardness after mechanical alloying and after thermal annealing, respectively.
Національний технічний університет України «Київський політехнічний інститут імені Ігоря Сікорського», Київ intermetallic σ-phase. An increase in V content from x = 0 to x = 1.5 changes the phase composition of the coatings and they consist of one bcc solid solution and σ-phases of different composition. With increasing content of V, the volume fraction of the σ-phase increases. The addition of V to AlCîNiFeCrTi shows the strengthening effect of the AlCîNiFeCrTiV 0-1.5 coatings and the Vickers hardness increased from 8,4 to 11 GPa.
The present study is primary addressed to structural evolution of multi-component AlCoNiFeCr highentropy alloy (HEA) from elemental materials to solid solution during mechanical alloying (MA), and further, to equilibrium phases during subsequent thermal annealing and pressure sintering. It was justified experimentally that MA of Al-Cu-Ni-Fe-Cr powder mixture during 5 hours resulted in a single-phase nanocrystalline HEA with a structure of ВCC solid solution. During thermal annealing recovery and recrystallization of the BCC solid solution take place at temperatures ranging from 130 to 500 °C, and phase transformation, and grain growth of equilibrium phases occur at higher temperatures. The phase composition transforms to BCC and FCC solid solutions when the MA powder was annealed at 600 °C for 1 h. The BCC and FCC solid solution structure can be maintained even after the alloy was annealed at 1000 °C. The alloy powder was consolidated by pressure sintering at 800 °C with 5 GPa pressure for half an hour. The sintered samples exhibit 9.2±0.3 GPa in Vickers hardness.
This study reports the investigation of high-entropy coatings obtained by electron-beam cladding in a vacuum of Al-Co-Ni-Fe-Cr-Ti-V x powder blend on a steel substrate. V was added to the Al-Cо-Ni-Fe-Cr-Ti equiatomic system and the effects of this added element on structure, phase composition and microhardness of AlCоNiFeCrTiV x high entropy coatings resulted from electron beam cladding were studied. The AlCоNiFeCrTiV 0 coatings consist of two solid solutions with ВСС1 and ВCC structure with different lattice parameters and a small volume fraction of -phase. It was shown that with increase in V content from x = 0 to x = 1.5, the phase composition of the coatings transforms from two solid solutions to a single ВCC solid solution and -phases of different composition. The phase volume fraction increased with an increase in the V content. The addition of V to AlCоNiFeCrTi shows the strengthening effect of the AlCоNiFeCrTiV 0.5-1.5 coatings and the Vickers hardness increased from 8,4 to 11 GPa. Microhardness of the coatings was affected by the sigma phase. The hardness enhancement can be likely attributed to the effect of solid solution strengthening and to the presence of -phase particles in the coating structure.
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