APPLICATION OF GRAIN-BOUNDARY ENGINEERING CONCEPTS TO ALLEVIATE INTERGRANULAR CRACKING IN ALLOYS-600 AND ALLOYS-690

Nickel-based alloys used in nuclear steam generator tubing have been f ound to be susceptible to intergranular stress corrosion cracking whil e in service. Following a recently developed model, grain boundary eng ineering concepts may be used to alleviate these concerns. This paper presents a report on the grain refinement approach in the proposed mod el 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 terna ry Ni-Cr-Fe alloy coatings. Electroplating conditions are given for th e production of Alloys 600 ana 690 having an average grain size in the range 100-250 nm.