CRYSTALLOGRAPHIC ANALYSIS OF BORIDES IN NI3AL BASE ALLOY IC6

A boride phase in a directionally solidified casting Ni3Al base alloy was investigated by means of scanning electron microscopy, transmissio n electron microscopy, X-ray mapping analysis, wavelength-dispersive X -ray analysis, electron energy loss analysis, energy-dispersive X-ray analysis and computer-aided dynamical diffraction simulation. This pha se was observed to occur in the interdendritic region of the as-cast i ngot. The chemical composition analysis and crystal structure studies revealed that the boride phase observed in the present alloy has a che mical formula of (Mo2Ni)B-2, and a body-centered orthorhombic crystal structure with lattice parameters a = 0.703 nm, b = 0.474 nm and c = 0 .312 nm. The space group of the phase was found to be Immm with the un it cell having 10 atoms which occupy the Wyckoff positions of Ni 2(a), Mo 2(b) and 2(c), and B 4(g).