Surface diffusion of tungsten and tungsten-rhenium alloys

The surface diffusion of pure tungsten, W-5sup(a)/sub(o)Re, and W-10sup(a)/sub(o)Re alloys at 25000C and 26500C in a nitrogen-hydrogen atmosphere was studied by the 'scratching-smoothing method'. Scratch profiles were measured by light interferometry. From the increases in scratch width with annealing time, surface diffusion constants were evaluated. The results show that the surface diffusion constant depends markedly on surface orientation and increases, on the average, with increasing rhenium content. It is concluded that this increase is far too small to account for the large difference in surface roughening between tungsten and tungsten-rhenium targets in x-ray tubes. (author)