The Effect of Microstructure and Dispersoids on the Mechanical Properties of NiAl Produced by Mechanical Alloying

Nickel aluminide (NiAl) alloys have been produced by mechanical alloying in highenergy attritor mill using elemental Ni and Al powder mixture. The mechanically alloyed powders (MA) were consolidated by hot extrusion technique, resulting in mate rials which were fully dense with a homogeneous distribution of oxide particles and a fine grain siz e of less than 1 m. A NiAl cast ingot was also hot extruded and investigated for comparison with the MA NiAl. The interesting microstructural feature of the as extruded MA NiAl is a bimodal istribution of the dispersoid particles, with average sizes of 10 nm and 100 nm. Examination of TEM micrographs of the as extruded MA NiAl showed that coarse particles are preferentially distribut ed on the grainboundaries whilst fine particles are dispersed throughout the grains. Mechanic al properties of MA NiAl have been studied by compressive testing at room temperature. The micros tru tures of the hot extruded materials were characterized to investigate the relationship between yield strength and microstructures of NiAl.