Effect of the Method of Introduction of Y_2O_3 into NiAl-Based Powder Alloys on Their Structure: I. Agitation in a Ball Mill

摘要

The effect of the sintering temperature (1100- 1400°C) of NiAl alloy samples with oxide Y_2O_3 produced by hydrostatic pressing on their structure and phase composition and the distribution of oxide paticles in a NiAl-based intermetallic matrix alloyed with -0.5 at % Fe is considered. It is found that dispersed oxide particles in the compact material prepared from a mixture of oxide Y_2O_3 powder and a NiAl alloy (produced by calcium hydride reduction of a mixture of nickel and aluminum oxides) powder in a standard ball mill are nonuniformly distributed in the volume. The morphology of oxides changes during sintering: sintered samples contain rounded particles, which differ strongly from the clearly faceted angular particles of oxide Y_2O_3 added to a mixture (they represent conglomerates of single crystals). In the sintered samples, large aggregates of oxides are revealed along grain boundaries. Mass transfer is possible at the NiAl/Y_2O_3 interface in the system: it leads to partial substitution of aluminum and/or iron atoms for yttrium atoms in the Y_2O_3 lattice and to the formation of submicroscopic particles of (Fe,Al)_5Y_2O_(12)-type oxides.