Predicting Chromium Depletion of Nickel Base Alloys

The effects of neutron radiation on nickel-based alloys

“…The addition of boron to Alloy 690 was modelled and shown to degrade the IGSCC resistance by lowering the minimum grain boundary chromium concentration and delaying the self-healing process. 42 This degradation in IGSCC resistance is seen to be less significant when a high density of intragranular carbides are present, presumably due to trapping of boron on said carbides. The effects of a lower grain boundary carbide coarsening rate, due to boron reducing the carbon solubility, are limited with regard to IGSCC susceptibility.…”

“…It is clear that even small traces of boron (∼10 wppm) may initially dominate helium production for the typical neutron spectrum of LWRs, with higher levels of boron significantly exacerbating the degradation in irradiated material properties. This, coupled with the modelling work of Faulkner and Bajaj, presenting boron's deleterious effects on IGSCC susceptibility, [41][42][43] indicates it is vital to ensure that the boron content, especially that of boron-10, in nickel-based alloys is as low as reasonably practical. The use of depleted boron is one option if boron additions are necessary.…”

“…39 Boron was found to increase grain boundary cohesiveness, thereby reducing the likelihood of brittle intergranular fracture. 40 Thermodynamic modelling work by Yin et al 41,42 has shown that with regard to grain boundary carbide precipitation, boron has two significant effects: increased carbide volume fraction and decreased carbon and chromium solubilities. Boron is shown to affect chromium diffusivity, carbide precipitation and change the grain boundary carbide coverage, affecting IGSCC susceptibility.…”