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

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Abstract
Static room-temperature Al-27 nuclear magnetic resonance (NMR) spectra for Tit-xAlx alloys in the range 0.25 less than or equal to x less than or equal to 0.55 are reported for the first time. The main resonances associated with the alpha(2) and gamma 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 less than or equal to x less than or equal to 0.48, resonances from both alpha(2) and gamma are observed. Careful quantitative analysis of the Al-27 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 gamma-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 C-Q = 8.15 MHz and an axial Knight shift anisotropy of 130 ppm. For the alpha(2) phase the centre-band simulation requires only an axial Knight shift anisotropy of 270 ppm and no quadrupolar interaction. An additional resonance associated with the gamma-phase is also detected and quantified, and this is attributed to aluminium on antisites