SITE DETERMINATION OF FE, CO AND CR ATOMS ADDED IN NI3AL BY ELECTRON CHANNELING ENHANCED MICROANALYSIS

Atom location by channelling enhanced microanalysis (ALCHEMI) under a planar channelling condition was performed to locate the ternary additions Fe, Co and Cr of about 5 at% in the intermetallic compound Ni3Al. It is concluded that the occupation site of Fe atoms depends on the chemical composition of the compound, i.e., the averaged Ni site occupancies of Fe in Ni70Al25Fe5, Ni72.5Al22.5Fe5 and Ni75Al20Fe5 are 70%, 42% and 23%, respectively. The Ni site occupancy of Co in Ni70Al25Co5 is 94%, but that of Cr in Ni75Al20Cr5 is 6%, showing that Co and Cr have strong preferences in the Ni and Al sites, respectively. These results are compared with previous results obtained by APFIM and ALCHEMI under an axial channelling condition and the predictions from thermodynamical consideration of the phase diagram. The accuracy of ALCHEMI under a planar channelling condition is also discussed for the L12-type ordered structure.