Effect of Mo on microstructural characteristics and coarsening kinetics of γ' precipitates in Co–Al–W–Ta–Ti alloys

Abstract

The solvus temperature, volume fraction, coarsening behavior of γ' precipitates and the partitioning behavior of alloying elements as well as lattice misfit of γ/γ' phases influence the creep behavior of Ni- and Co-base superalloys. However, few investigations about the microstructural characteristics and the coarsening behavior of γ' precipitates were reported in multicomponent novel Co-base superalloys during thermal exposure. Two alloys containing different contents of molybdenum and tungsten have been investigated to explore the effect of molybdenum on γ' solvus temperature, γ+γ' microstructure and γ' coarsening in Co–Al–W–Ta–Ti-base alloys. The results showed that the γ' solvus temperature decreases with the addition of Mo. Mo addition reduces the γ' volume fractions after aging above 1000°C, but results in negligible influence on the γ' volume fractions aging at 900°C. Meanwhile, γ' coarsening is controlled by diffusion in experimental alloys after aging at 900°C and 1000°C, and the kinetics of γ' growth in experimental alloys are consistent with the predictions of LSW theory.