Study of V-Be diffusion couple by ion backscattering

Ion backscattering has been used to study the diffusion couple V-Be at annealing temperatures in the range 800 to 1100 K. Analysis of proton and helium backscattering allowed determination of the average composition versus depth following in situ isothermal anneals of thin vapor-deposited vanadium films on beryllium substrates. The results were interpreted as an initial diffusion governed by grain boundary migration of the beryllium through the vanadium to form a beryllium oxide surface layer. Vanadium was found to be excluded from the beryllium oxide surface layer and also from the native oxide on the beryllium substrate. The initial rapid diffusion along grain boundaries was followed by a slower diffusion into the vanadium grains. The amount of beryllium which diffused into the vanadium film obeyed a tsup(1/2) dependence where t is the anneal time. Complete anneal sequences were taken at two temperatures and a tentative activation energy for the diffusion of beryllium in bulk vanadium of 3.4 eV was determined. The diffusion coefficient was estimated to be 1.0 X 10-17 cm2/sec at 958 K and 0.8 X 10-18 cm2/sec at 903 K. (Auth.)