Dislocation dynamics simulations of precipitation-strengthened Ni- and Co-based superalloys

Two-dimensional dislocation dynamics (DD) simulations are carried out to simulate the increase in yield stress of nickel- and cobalt-based superalloys by order-strengthened γ'(L12)-precipitates, under conditions where precipitates are sheared and/or looped by single and super-dislocations. Parametric studies are performed for precipitate volume fractions between 5 and 70% and radii between 1 and 100 nm, resulting in yield stress increments due to a mixture of precipitate bypassing and shearing by single and super-dislocations of edge or screw character. DD yield stresses are compared to a variety of analytical models for strengthening by ordered precipitates showing that the closed-form solutions do not agree with DD predictions over all regimes of precipitate sizes and volume fractions. The DD yield stresses, converted to hardness values, are also compared to experimental hardnesses from archival literature on binary Ni-13Al (at. %) as well as Ni-10Al-8Cr(-2 W) (at.%) alloys aged at various temperatures and times, for which γ'(L12)-precipitate radii and volume fractions had been measured via atom-probe tomography and scanning electron microscopy. DD predictions are within 5-10% of experimental hardnesses in underaged alloys, but they typically overestimate hardness for peak and overaged samples. Finally, DD is used to predict the hardnesses for a γ'(L12)-strengthened Co-8.8Al-7.3 W (at. %) superalloy for 50-130 nm average precipitate radii within 10% of experimental values.