*Article* **Microstructural Changes in Ni-Al-Cr-Based Heat-Resistant Alloy with Re Addition**

**Nina A. Koneva 1, Elena L. Nikonenko 1, Alisa V. Nikonenko <sup>2</sup> and Natalya A. Popova 1,\***


**Abstract:** This paper presents scanning and transmission electron microscope investigations of the structure, phase composition, and morphology of a heat-resistant alloy modified by thermal treatment and additionally alloyed by rhenium. The rhenium alloy was obtained by using the directional crystallization technique. The structural investigations were carried out for two states of the alloy, i.e., (1) original (after the directional crystallization); (2) after the directional crystallization with 1150 ◦C annealing for 1 h and 1100 ◦C annealing for 480 h. It is shown that fcc-based γ- and γ -phases are primary in all states of the alloy. The γ -phase has an L12 structure, while γ-phase is a disordered phase. It was found that after directed crystallization, the volume fraction of the γ phase is ~85%, the fraction of the γ-phase is less than 10%. Annealing leads to an increase in the γ - phase up to 90%, the proportion of the γ-phase practically does not change. Rhenium is a phase-formation element. The investigations show that high-temperature annealing modifies the structural and phase conditions of the heat-resistant alloy.

**Keywords:** aluminum; nickel; superalloys; γ - and γ-phases; close-packed phases; rhenium

**Citation:** Koneva, N.A.; Nikonenko, E.L.; Nikonenko, A.V.; Popova, N.A. Microstructural Changes in Ni-Al-Cr-Based Heat-Resistant Alloy with Re Addition. *Crystals* **2021**, *11*, 89. https://doi.org/10.3390/cryst 11020089

Academic Editor: Wojciech Polkowski Received: 29 December 2020 Accepted: 18 January 2021 Published: 21 January 2021

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