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After solutionizing and aging at 980°C for various durations, the compressive deformation behaviour and mechanisms of the directionally solidified nickel-based superalloy CM247LC are investigated at room temperature. Experimental results show that the yield strength decreases gradually from 991 ± 1.2–672 ± 7.5 MPa with increasing the γ′ precipitate size from 145 ± 2–604 ± 19 nm. Transmission electron microscope observations on the slightly deformed specimens reveal that, in contrast to previous researches, plastic deformation of all the specimens is controlled by strongly coupled dislocations cutting through γ′ precipitates. Based on these experimental results, the relationship between the yield strength and precipitate size is discussed. [ABSTRACT FROM AUTHOR]