Tensile deformation mechanisms in a new directionally solidified Ni-base superalloy containing coarse γ′ precipitates at 650 °C

A new directionally solidified Ni-base superalloy, M4706, containing three different model microstructures is obtained via changing aging heat treatments. After tensile deformation at 650 °C, the microstructures are investigated by scanning electron microscope and transmission electron microscope. Experimental results reveal that the tensile strength decreases gradually with increasing mean γ′ precipitate size from 424 to 734 nm, and plastic deformation is accomplished mainly by dislocations shearing of γ′ precipitates in all three microstructures. Meanwhile, it is also found that as the precipitate size increases, more and more dislocations pass through both γ and γ′ phases in groups in the slightly deformed specimens. Based on these results, it is deemed that the occurrence of this deformation pattern accounts for the degeneration of the yield strength with precipitate size.