Evaluation on elevated-temperature stability of modified 718-type alloys with varied phase configurations

摘要

Inconel 718 is a Ni–Fe-based superalloy widely used in aerospace engines because of its excellent mechanical properties.However,the inferior stability of theγ″phase limits the application of Inconel 718,which coarsens rapidly at temperatures greater than 650°C.Further improving the temperature tolerance of Inconel 718 requires optimization of the phase configuration via modification of the alloy’s chemical composition.Given the aforementioned objective,this work was conducted to study the precipitation behavior and thermal stability of the strengthening phases with various structures in modified Inconel 718 alloys by tailoring the Al/Ti ratio.With increasing Al/Ti ratio,three particle configurations were formed:γ′/γ″composite,isolatedγ′,andγ′/γ″/γ′composite particles.The results of aging tests demonstrate that the isolatedγ′and theγ′/γ″/γ′composite structure exhibited better thermal stability at temperature as high as 800°C.The isolatedγ′exhibited a reduced coarsening rate compared with theγ′/γ″/γ′composite particles because the isolatedγ′phase was rich in Al,Ti,and Nb.However,theγ′/γ″composite particles coarsened and decomposed rapidly during aging at temperatures greater than 700°C because of the lower stability resulting from the larger number ofγ″particles.The obtained results provide necessary data for the compositional optimization of novel 718-type alloys.