Abstract
Auger Electron Spectroscopy and Secondary Ion Mass Spectrometry were used to study surface and grain boundary segregation of B and S in Ni. Sulfur segregation was not influenced by the presence of boron and resulted in a uniform monolayer surface and grain boundary coverage. Segregation of boron differed from that of sulfur and resulted in the precipitation of Ni 3B in the near surface layer. At temperature analysis showed that bondes dissolved into the matrix at temperatures above 923 K and precipitated during cooling. This process did not affect the segregation of sulfur, which covered the bondes and matrix uniformly. Grain boundary segregation of boron, its effect on the co-segregation of sulfur and on the tendency for intergranular fracture were studied using hydrogen charged in situ fractured samples. Addition of boron to Ni reduced the tendency for intergranular fracture. A small amount of boron was found at the grain boundaries, together with sulfur and carbon; the sulfur and carbon levels were about 20% smaller than in the boron-free sample. These results suggest that boron has a beneficial effect on the strength of the grain boundaries and also reduces the negative effect of sulfur segregation on the boundary properties.
Published Version
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