Grain boundaries of nickel

Figure 2. Histogram of sulfur coverages at grain boundaries of vacuum-melted nickel after two different heat treatments (39).

Niobium, when added to AUoy 182, stabilizes the carbon content and prevents the precipitation of Cr carbides at the grain boundary [78]. C, P, Si, and S segregate or precipitate at the grain boundary and are critical to hot-cracking resistance of nickel-based weld metals [79]. When Si segregates at the grain boundaries of austenitic stainless steel. 

Figure 21. Concentration of Cr, Fe, Ni and P across a grain boundary in nickel-base alloy Inconel 690.

Yttrium, on the otlrer hand, which has a larger cation radius than Cr +, appears to affect the grain boundary cation diffusion and not the volume diffusion of Ni +. The effects of the addition of small amounts of yttrium to nickel is to decrease dre rate of tire low temperamre grain-boundary dominated oxidation kinetics. 

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