Solid State Reaction Mechanism and Microstructure Evolution of Ni-Al Powders during High Energy Ball Milling Revisited by TEM

Abstract

Microstructure evolution during the formation of B2-NiAl by high energy ball milling of equiatomic elemental mixtures was studied by X-ray diffractometer, scanning electron microscopy, and transmission electron microscopy (TEM). The crystallite size, lattice defects and ordering of the B2-NiAl were monitored via TEM as function of milling time. The diffusion reaction, Ni+Al→NiAl3 or/and Ni2Al3, occurred during high energy ball milling, and to a certain extent offered the stored energy for the explosive exothermic reaction, Ni+Al→B2-NiAl. The fine microstructure of newly formed B2-NiAl after 5 h milling involved high density defects, e.g. antiphase boundary, long range ordering domains, vacancies, and dislocations.

Effect of the Particle Size of Al/Ni Multilayer Powder on the Exothermic Characterization

“…Figure 10 shows the XRD analysis results of the under 75 µm (75 µm) and over 850 µm (850 µm) classified Al/Ni multilayer powders after the exothermic reaction. NiAl phase with a B2 crystallographic structure [ 21 , 30 , 31 , 32 ] was identified in both powders, confirming the formation of the NiAl intermetallic compound, and clear peaks of other intermetallic compounds have not been confirmed in the XRD analysis. As mentioned earlier, the enthalpy formation of the NiAl phase was larger than that of other intermetallic compounds of the Ni–Al system alloy [ 8 , 33 , 34 ].…”

Oxidation behavior of dense Yttrium doped B2-NiAl bulk material fabricated by ball milling self-propagating high-temperature synthesis and densified by spark plasma sintering

“…It is well known that Ni and Al belong to the combination of ductile-ductile metals, which are first cold-welded during milling, workhardened and fragmented due to induced brittleness. It has also been demonstrated by TEM analysis that the NiAl synthesis mechanism during milling is diffusion controlled so that before the formation of B2-NiAl, additional phases, such as NiAl3, Ni2Al3 are formed as the deformation energy is stored before the ignition reaction of NiAl takes place [46].…”