Detection of phase and antisite structure of Ti–Al alloys by27Al solid state nuclear magnetic resonance

Static room-temperature 27Al nuclear magnetic resonance (NMR) spectra for Ti1−xAlx alloys in the range 0·25 ≤ × ≤ 0.55 are reported for the first time. The main resonances associated with the α2 and γ phases are clearly identified. The spectra follow the phase distribution in that, for samples annealed at 1473 K for 6h in the range 0·43 ≤ × ≤ 0·48, resonances from both α2 and γ are observed. Careful quantitative analysis of the 27Al NMR spectra indicates that from single-phase samples all aluminium nuclei from the central transition are recorded, whereas for two-phase samples there is a loss of signal that is a consequence of the two-phase alloy microstructure. For the γ-phase the NMR centre band shows a distinctive, largely second-order quadrupolar line shape together with associated satellite transitions which yield a quadrupolar coupling constant CQ = 8·15 MHz and an axial Knight shift anisotropy of 130ppm. For the α2 phase the centre-band simulation requires only an axial Knight shift anisotropy of 270ppm and no quadrupolar interaction. An additional resonance associated with the γ-phase is also detected and quantified, and this is attributed to aluminium on antisites.