AL-27 NUCLEAR-MAGNETIC-RESONANCE DETECTION OF DIFFUSION-PROCESSES IN NI1-XALX ESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-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 give s 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 tak en 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 d iffusion 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 report ed 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 transiti on was detected by means of powder x-ray diffraction or thermal analys is. These observations are discussed qualitatively in terms of defect- assisted diffusion processes.