Micros tructure and Strength of B 2 ~ 0rdered NiAl(Ta) containing Ni2Al Precipitates

Precipitation of Ni2Al in supersaturated NiAl containing Ta and corresponding hardening have been investigated by hardness measurements and by transmission electron microscope observations. Selected area electron diffraction, high resolution electron microscopy and energy dispersive X-ray spectrometer analysis have shown that the Ni 2 Al with a hexagonal structure precipitates coherently in the B2~NiAl matrix. Ni 2 Al is an ordered phase with a u nit cell parameter, aNi 2 Ai= -\/2 aNiAi and CNi 2 Ai= V공aNiAi. The orientation relationship between the Ni 2 Al precipitate and the B2-NiAl matrix is (0001)Ni 2 Ai//(111)niai a n d 〔l l5 o 〕Ni2Ai//U 1 0 〕 NiAi. NiAl hardens appreciably by the precipitation of Ni 2 Al phase.