Relationship between Ti/Al ratio and stress-rupture properties in nickel-based superalloy

Microstructural analyses have been carried out to investigate the relationship between Ti/Al ratio and stress-rupture properties of nickel-based superalloy Ni–19.5Cr–(0.8–3.5)Al–(0.5–3.2)Ti–0.06C. The γ′ phase coherently precipitates in the γ matrix, the volume fraction and average diameter of the spherical γ′ phase decrease slightly with the increase of Ti/Al ratio after full heat treatment. The precipitate of β-NiAl in the γ matrix for the alloys with low Ti/Al ratio leads to the propagation of cracking into the grain interior. High Ti/Al ratio leads to the precipitate of η-Ni3Ti at grain boundaries, which weakens the strength of grain boundaries. Both the precipitates of β-NiAl and η-Ni3Ti phases are harmful to the stress-rupture life and a peak stress-rupture life appears when Ti/Al ratio is about 1.22 with elongation and reduction in area higher than 5% and 9.7%, respectively.

► Low Ti/Al ratio leads to the precipitate of β-NiAl in the γ matrix.
► High Ti/Al ratio leads to the precipitate of η-Ni3Ti at grain boundaries.
► The precipitates of β-NiAl and η-Ni3Ti are harmful to the stress-rupture life.
► A peak stress-rupture life appears when Ti/Al ratio is about 1.22.