CONTRIBUTION OF NANOSIZED STRUCTURAL AND PHASE ELEMENTS FORMED AT DIFFERENT STAGES OF PREPARATION AND TREATMENT INTO THE HIGH-TEMPERATURE STRENGTH CHARACTERISTICS OF POWDER STRUCTURAL ALLOYS OF THE NIAL-Y2O3 SYSTEM

The NiAl-Y2O3 alloys were used to study the role of ultrafine and nanosized structure-phase states formed in the system at the stage of the preparation of initial powder mixtures, compaction and thermomechanical treatment ensuring the formation of directional structures of the compact material. The initial NiAl powders were obtained by hydride calcium recovery (HCR) of nickel oxide and aluminum oxide mixtures. The HCR NiAl powders were mechanoactivated in an attritor and in a ball mill. The structure of powders, their specific surface area, level of microdistortions, and coherent domain size were studied as a function of mechanoactivation time. It is shown that the specific surface of the powder processed in the attritor for 10-15 hours is higher by a factor of 1.7-1.8 than that of the powder processed in a ball mill for 150 hours. The level of microdistortions and coherent domain size of the powders milled for 15 hours in the attritor are 4.5x10-3 and 15 nm, respectively, while those of the powders treated in the ball mill for 150 hours are 1.9x10-3 and 29 nm, respectively, i.e., the degree of work hardening after short-term treatment in the attritor is about twofold higher than that is after long-term ball milling. The study of the distribution of Y2O3 oxide in the compact material as a function of the method of its introduction into the HCR NiAl powder showed that the ball milling does not provide a uniform distribution of the oxide particles in the NiAl powder. The combination of the mechanoactivation of the HCR NiAl powder mixture with the introduction of fine oxide powder particles into attritor allowed us to obtain hot extruded alloy samples free from aggregates of fine oxide particles at grain boundary junctions. Subsequent recrystallization of the samples at temperatures of ~ 0.89-0.95 Tm (K) of NiAl in isothermal conditions or in a temperature field with a temperature gradient along the length of the product allowed us to obtain the alloy samples with a small fraction of transverse boundaries. Such structure provides a high creep resistance at temperatures up to 1500-1550ºC.

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