Order strengthening in the cast nickel-based superalloy IN 100 at room temperature

The isothermal aging behavior of the cuboidal ordered γ′ precipitates of the cast nickel-based superalloy IN 100 was investigated at temperatures between 800 and 1000°C. Despite the complication connected with morphological changes of the γ′ particle microstructure due to coarsening and raft formation a classical Ostwald ripening law was confirmed. Comparing the calculated critical resolved shear stress (CRSS) increase with the experimental data exhibits the functional dependencies on the mean γ′ size as predicted by theory [B. Reppich, in: R.W. Cahn et al. (Eds.), Materials Science and Technology, vol. 6, in: H. Mughrabi (Ed.), Plastic Deformation and Fracture of Materials, Wiley-VCH, Weinheim, Germany, 1993, pp. 311–357]: (a) a parabolic increase of the CRSS for cutting of fine under-aged γ′ particles (weak pair-coupling); (b) a transition to cutting by strongly pair-coupled dislocations for increasing particle sizes; and (c) a deviation from the hyperbolic CRSS decrease due to strong pair-coupled cutting towards Orowan by-passing for non-coupled single dislocations at over-aged particles.