We have studied the structure and mechanical properties of eutectic alloys β-NiAl + γ-Re of the ternary system Ni − Al − Re. We have established that the best combination of mechanical characteristics, determined by local loading with a rigid indentor, is exhibited by the alloy containing 2.5 at.% Re, the structure of which consists of the eutectic β-NiAl + γ-Re. Rhenium inclusions can inhibit movement of cracks in the material, and also can play the role of traps for cracks. Brittle intercrystallite fracture is characteristic of the alloy consisting of one-phase intermetallic NiAl. Mixed fracture is typical of the eutectic alloy β-NiAl + γ-Re, with transcrystallite cleavage predominating. We have shown that plastic interlayers of a rhenium phase within the microstructure increase the crack resistance of a detonation coating made from eutectic alloys β-NiAl + γ-Re.Nickel aluminide NiAl, having (along with high scaling resistance (up to 1400°C)) a density 1.35 times lower and a thermal conductivity 4 times higher than nickel superalloys, is a promising compound to use as a basis for developing new structural materials and protective coatings for gas turbine engines for aviation [1][2][3]. Major factor holding back widespread use of materials based on nickel aluminide is lack of plasticity at room temperature and low crack resistance.Progress in improvement of the class of materials under consideration is mainly connected with development of the optimal composite structure by introducing alloying components into their composition: Cr, Mo, Nb, V, Ti, Ta, etc.[4-6]. One such promising component is rhenium, which as we know [9-11] has an unusual combination of unique characteristics: high modulus of elasticity, high recrystallization temperature, high fatigue strength. From experience using rhenium in superalloys, we know [3,4] that introducing rhenium into a material may simultaneously increase both the strength and the plasticity. Moreover, rhenium makes it possible to form eutectic structures that often have more fortunate combination of characteristics, compared with other structural composites. A slight amount of rhenium is contained in an NiAl solid solution (0.2 at.%) [9].Our previous investigations [11] allowed us to determine the limits of the region of existence for eutectic alloys β-NiAl + γ-Re that are two-phase in crystallization. From this region, we have selected alloys containing from 0.2 to 3.0 at.% rhenium in order to assess the mechanical properties of β-NiAl + γ-Re eutectic alloys and coatings sprayed from powders, obtained from the ingots by mechanical crushing. EXPERIMENTAL SECTIONThe alloys were melted in an electric arc furnace with a nonconsumable tungsten electrode on a water-cooled copper hearth in a purified argon atmosphere. The elemental distribution in the structure was determined using a Camebax SX-50 electron probe microanalyzer (France). In order to assess the mechanical properties of the materials, we used the method of local loading by a rigid indentor [9], including plotting of the...
621.793We have studied phase formation in detonation coatings sprayed from Ti − 50 at.% Al powders. The powders of the alloy were obtained by various methods: crushing an ingot and mechanical alloying of Ti and Al. Using polyphase nanostructural materials activated by mechanical alloying makes the process of phase formation in the gas-thermal sprayed coatings based on them more general-purpose and controlled due to the more active and more subtle reaction of the material with the gaseous atmosphere.We have shown that from mechanically alloyed Ti − 50 at.% Al powder, using the detonation-gas spraying method we can consolidate a coating based on Al 2 TiO 5 by oxidizing action of the working gas on the powder and also a coating based on titanium aluminides with TiN inclusions by nitriding action.The phase composition of the cast microstructural γ-TiAl powder is inherited by the coating.
The paper examines the phase formation of detonation coatings sprayed from mechanically alloyed . It is shown that coatings with different phase compositions and functional properties can be consolidated from this activated powder by varying process conditions (including gas composition during detonation spraying). Three types of composite coatings with different structures are obtained: TiB and TiB 2 inclusions are distributed in an intermetallic matrix (Al 3 Ti, γ-TiAl); inclusions of oxides and oxynitrides are additionally present in the same structure; inclusions of borides, Al, and Ti are distributed in a mixture of intermetallic and nitride (TiN, AlN) phases.
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