GRAIN BOUNDARY SEGREGATION AND GRAIN SIZE DEPENDENCE OF STRENGTH OF NICKEL-SULFUR ALLOYS

Tensile, miorohardness and autoradiographic observations of Ni-S alloys containing <1 to 50 ppm S indicate that sulfur is strongly segregated to grain boundaries in nickel. For all but the most concentrated of these alloys the sulfur appears to be in solid solution. This non-equilibrium sulfur enrichment of the grain boundaries appears to occur via a solute-vacancy interaction mechanism. This segregation causes a local increase in microhardness and an unusual variation of the Petch slope k in the grain size dependence of the flow stress. The latter can be qualitatively rationalized by an extension of Li's model of dislocation generation from grain boundary ledges. © 1969.