Structural-phase state of powder alloys based on Ni and Al at different annealing temperatures

The creation of new generation materials is caused by the need to increase the operating time of parts and structural elements at the highest possible temperatures, as well as to reduce the specific gravity of materials. Therefore, intermetallic compounds based on NiAl, which, due to the combination of physical and mechanical properties, are promising for long-term operation at high operating temperatures. It is well known that NiAl has excellent environmental resistance at all temperatures and is a compound with extremely high oxidation resistance compared to other high temperature alloys and materials. In the alloy under study, special attention is paid to the effect of impurities. This was necessary because the use of even small additions of the third component is often a decisive factor in the development of alloys with different mechanical properties. In addition, additives of the third component can distort the crystal lattice, fine structure, and cause the formation of metastable compounds. The temperature of the homogenizing annealing also plays an important role. The phase composition and morphology of the annealed powder alloy based on the NiAl intermetallic compound were studied by the methods of transmission diffraction electron microscopy and X-ray diffraction analysis. The sintering temperature varied from 1100 ° C to 1400 ° C. The chemical composition of the alloy in the sintered unannealed state mainly contained nickel and aluminum. Chemical composition of the investigated alloys before and after annealing, except for the main elements (nickel and aluminum), included oxygen - up to 7.3%, yttrium - up to 1.3%, and iron -up to 0.65%. The work investigated the effect of the of homogenizing annealing on the structural-phase state of the powder alloy. It was found that the bulk of the alloy is formed by the B2 superstructure, consisting of Ni and Al. The NiAl phase consists of grains, the boundaries of which contain various oxides, namely, FeYO3 and (Fe, Al)sYsO12. Inside the grains of the NiAl phase, both before and after of homogenizing annealing, there are nanoscale particles of the YAl phase on dislocations. Also, studies have shown that the composition of the alloy at almost all annealing temperatures corresponds to the NiAl phase with the B2 superstructure. The state of long-range atomic order in the NiAl phase increases to 1 with an increase in the annealing temperature to 1400°C.Internal elastic stresses are low.

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