Effect of Cu on microstructure and tensile property of an Al-modified Ni-based superalloy

Cu element exhibits a relatively low heat of combustion, which proves to be beneficial for enhancing the resistance to oxygen-rich combustion of superalloys, and in the present study we investigate the effect of Cu on microstructure and tensile properties of an Al-modified K4061 superalloy. The findings indicate that the grain size increases with the addition of Cu. Furthermore, the precipitated strengthening phase is the spherical gamma ' phase, with its size and content initially decreasing and thereafter increasing with increasing Cu content. Notably, Cu can segregate to form the nano Cu-rich clusters which directly precipitate from liquid and mainly distribute in the gamma ' phase. Overall, Cu is detrimental to the strength of the Al-modified K4061 alloy. The strengthening mechanism is quantitatively analyzed, encompassing grain boundary strengthening, solid solution strengthening and precipitation strengthening. The addition of Cu leads to an unaltered contribution to strength from grain boundary and solid solution strengthening. Nevertheless, the dominant deformation mechanism transforms from Orowan looping to ordered shearing and subsequently reverts to Orowan looping. Meanwhile, the mechanical property of the Al-modified K4061 alloys with higher Cu content decreases due to a reduction in the strength increment attributed to precipitation strengthening.