27A1 Nuclear Magnetic Resonance Detection of Diffusion Processes in Ni1-xAlx (0.46<=x<=0.54) and Ni2Al3

The alloy system Ni1-xAlx has been investigated by means of Al-27 NMR around the equiatomic region where x = 0.5, and at x = 0.6, which gives the trigonal ordered compound Ni2Al3. For Ni2Al3, two At sites were clearly resolved at room temperature by means of their characteristic second-order quadrupolar structure. NMR spectra for cubic Ni1-xAlx taken at temperatures up to 960 degrees C show rapid Al-27 Line narrowing above similar or equal to 600 degrees C for x = 0.54 (indicative of diffusion processes), but no such line narrowing was observed up to 960 degrees C for x = 0.50 or x = 0.48. Ni-61 NMR results are also reported for the equiatomic alloy. For Ni2Al3, the Al-27 NMR powder pattern evolved smoothly into that characteristic of one well defined site as the temperature was raised to 820 degrees C although no phase transition was detected by means of powder x-ray diffraction or thermal analysis. These observations are discussed qualitatively in terms of defect-assisted diffusion processes.