The phase and structural transformations in equiatomic powder compositions of the Al-Cu-Ni-Fe-Cr system during mechanical alloying (MA), annealing and subsequent spark plasma sintering (SPS) had been studied by X-ray diffraction analysis, scanning and transmission electron microscopy, and differential scanning calorimetry. It has been established that the nanocrystalline high-entropy AlCuNiFeCr alloy synthesized during MA consists of a supersaturated solid solution with a bcc crystalline structure. After annealing and spark plasma sintering at 800 C, the alloy becomes three-phased, and consists mainly of one B2-ordered solid solution, one fcc solid solution (25 wt %), and of the (Сr, Fe) 23 C 6 phase (8 wt %). The Vickers hardness of the sintered AlCuNiFeCr alloy was 8.35 GPa, and the compressive strength at room temperature reached 1960 MPa.

In this work, solid-state mechanical alloying (MA) and cold spraying (CS) processes were applied to fabricate powder AlNiCoFeCrTi high-entropy alloy (HEA) and then to produce HE coatings on steel substrate. Shot-time MA for 3 h has been employed to synthesize nanostructured equiatomic AlNiCoFeCrTi HEA of metastable supersaturated substitutional solid solution with bcc crystal structure. Although alloying is not complete at this shot milling time, it goes to completion during thermal annealing to achieve the alloy formation. XRD study on mechanically alloyed high-entropy AlNiCoFeCrTi alloy after thermal annealing at 1200 °C for 1 h revealed the formation of a three-phase structure consisting of ordered bcc phase with fine precipitates of intermetallic σ-phase (FeCr) and titanium carbide TiC. The powder agglomerates resulted from annealing were grinded in a ball mill for 1 h. Nanostructured disordered bcc solid solution, TiC and σ-phases are noticed after milling. Coatings of 450 μm in mean thickness were deposited by the CS process using an air like a working gas, temperature and pressure of 450 °C and 0.9 MPa, respectively. The experimental results confirm that CS process can be used to produce HE coatings with low porosity. As a low-temperature deposition process, CS completely retained the HEA phase composition and nanostructure in the coating without any phase transformation. The AlFeNiCoCrTi HE coatings exhibit 10.3 ± 0.3 GPa in Vickers hardness.

Металлофиз. новейшие технол. / Metallofiz. Noveishie Tekhnol. 2014, т. 36, № 4, сс. 477-490 Оттиски доступны непосредственно от издателя Фотокопирование разрешено только в соответствии с лицензией 2014 ИМФ (Институт металлофизики им. Г. В. Курдюмова НАН Украины) Напечатано в Украине.

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