Study of molybdenum effect on synthesis behavior of nanocrystalline NiAl intermetallic during mechanical alloying

The mechanical alloying (MA) procedure was used to synthesize the Ni50Al50 and Ni50Al45Mo5 nanocrystalline intermetallic compound using the pure Ni, Al and Mo elemental powders under an argon atmosphere for different times (8, 16, 48, 80 and 128 h) in a planetary ball mill with hardened steel balls (12 balls-1cm and 4 balls-2cm in diameter). The mechanical alloying was carried out in the attendance of various Mo contents as a micro-alloying element for various milling times. Microstructural characterization and structural changes of powder particles during mechanical alloying were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Outcomes confirmed that the synthesis behavior of NiAl intermetallic depends on the milling time and Mo content. The results show that after than 80h milling, the intermetallic phase is produced after opening the vial lid. X-ray map show that, in the fixed milling time, enhancing the Mo content leads to acceleration in the NiAl formation in air atmosphere. The mechanical alloyed powders have a microstructure consisting of nanometer size particles. Mo enhance has a considerable effect on the lowering of crystallite size. The TEM image showed that the Ni50Al45Mo5 nano-particles were less than 10 nm. The average grain size is smaller than those sizes obtained in the NiAl (25 – 35 nm) alloy.