Effect of specimen size on creep crack growth rate in superalloys IN625 and IN783

Abstract

To further clarify the relation between the intensity of specimen size effect on creep crack growth (CCG) rate and operative creep fracture mechanisms, CCG testing and mechanism observation were carried out for two superalloys IN625 and IN783. Results show that the CCG data of different specimen types for IN625 basically coincide at 650 °C. In contrast, strong specimen size effect was observed in IN783 at 560 °C, that is, the CCG rate increases with the increase in specimen thickness, producing the largest CCG ratio of approximately seven. The load-line displacement and fracture mechanism analyses indicate that the IN625 specimens failed in a ductile and intergranular manner, while the IN783 specimens in a brittle and intergranular manner. The present study suggests that the influence of creep fracture mechanisms should be considered in the characterization of the specimen size effect on CCG rate.