Application of grain boundary engineering concepts to alleviate intergranular cracking in Alloys 600 and 690

Nickel-based alloys used in nuclear steam generator tubing have been found to be susceptible to intergranular stress corrosion cracking while in service. Following a recently developed model, grain boundary engineering concepts may be used to alleviate these concerns. This paper presents a report on the grain refinement approach in the proposed model which results in a higher probability of arresting stress corrosion cracks before reaching a critical length at which failure occurs. For this purpose, an electroplating system was developed to produce ternary Ni-Cr-Fe alloy coatings. Electroplating conditions are given for the production of Alloys 600 and 690 having an average grain size in the range 100-250 nm.