Effect of Ta on solidification characteristics and mechanical properties of DZ411 Ni-based superalloy

The effects of Ta content(2.72wt.%, 3.10wt.% and 4.00wt.%) on the solidification characteristics and mechanical properties of directionally solidified DZ411 Ni-based superalloys were investigated. It is found that the content of Mo decreases with the increase of Ta in liquid phase after directional solidification, indicating the addition of Ta can reduce the element segregation in alloys. The primary and secondary dendrite arm spacings(PDAS and SDAS) of the DZ411 alloy increase with the addition of Ta, which are consistent with the models by Hunt and Wagner. The increase of PDAS and SDAS can provide enough space for the growth of tertiary dendrite arms, which hinders the growth of unfavorably oriented primary dendrites. As a result, the addition of Ta facilitates the growth of favorably oriented dendrites. More MC carbides and γ-γ' eutectics are formed in the interdendritic regions, which is attributed to the segregation of Ta in the liquid phase. Furthermore, the degree of supersaturation of W, Mo in γ matrix increases with the increase of Ta, thus, the addition of Ta promotes the formation of TCP phase. The addition of Ta also increases the microhardness in both the primary dendrite and interdendritic regions of the alloy, and the microhardness of the primary dendrite is closer to that in interdendritic regions with the increase of Ta.