EFFECT OF WORK HARDENING AND NANOSTRUCTURING UPON SHORT-TERM MECHANICAL ACTIVATION OF RU-AL AND NI-AL POWDER MIXTURES ON THE STRUCTURE OF COMPACT SINTERED SAMPLES

A. Morozov, A. Drozdov, K. Povarova, E. Galieva

Abstract

The effect of mechanoactivation (MA) of initial Ru-Al and Ni-Al powder mixtures on the structure of sintered compact samples has been studied. After MA in the attritor, the constitution of the powder mixture of two ductile fcc metals (Ni and Al) was compared with that of ductile Al and hardly deformable hcp Ru. The maximum processing time was 16 hours. According to the broadening of XRD peaks, the treatment of the Ni (Ru)-Al powder mixtures in the attritor increases the level of internal stresses and the number of defects, i.e., is accompanied by strain hardening of the material. Upon MA of the Ni-Al powders for up to 8 h, both metals are intensely strain hardened and form large granules. The destruction of the layered composite granules upon further MA is caused by increased dislocation density in each metal, the accumulation of defects, refinement of coherent domains, and the attainment of the critical degree of deformation. The strain hardening of both Ru and Al reaches maximum after MA for 5 hours and then does not virtually change. The growth of internal stress, the increased dislocations density in ductile metals, the refinement of coherent domains, the increased contact area between the metals, and the shortening of diffusion paths (Al in Ni and Ru) decrease the start interaction temperature. The contact interaction between Ru (Ni) and Al even in the samples free from MA in the attritor (A0) was shown to begin already in the solid phase at 600-620°C, i.e., at temperatures below the temperatures of the eutectic reactions with the participation of liquid Al. The exothermic peaks of the RuAl formation from Ru and Al and the NiAl formation from Ni and Al decrease with increasing MA time. The compact samples prepared by pressure sintering of mechanoactivated powder mixtures are characterized by macro- and microuniformity of the distribution of micron- and submicron-size phase precipitates over the entire volume of material. The completion of the reaction alloy formation requires annealing at temperatures of at least 0.8Tm (K).

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