Effect of Mo Addition on the Formation of Nanocrystalline NiAl Intermetallic during Mechanical Alloying

Nickel aluminids are compounds with good properties such as high melting point, high strength to weight ratio and high corrosion resistance especially at high temperatures. In this study, the effect of adding Mo with atomic percentages 1, 2.5 and 5 to the nanostructured alloy with chemical composition Ni50Al50 in a planetary mill were studied for times of 8 and 16 h. The structural changes of powder particles during mechanical alloying were investigated by X-ray diffractometery and scanning electron microscopy. The crystallite size and lattice strain milled powder particles was calculated using X-ray diffraction analysis and applying methods Williamson-Hall. The results showed that the addition of Mo in the NiAl alloy refined the NiAl grains obviously. Crystallite size decreased with increasing molybdenum content, so that in NiAl samples without Mo after 16 h milling, the crystallite size was more than 100 nm and with increasing molybdenum to 5 at.%, this value was reduced to 65 nm. Also the lattice strain has increased at first and then reached to a constant value with increasing molybdenum.