Research Progress on Topologically Close-Packed Phases of Aluminide Coatings

Abstract

Aluminide coatings are used for high temperature protection of aeroengine and gas turbine blades due to their excellent high temperature oxidation resistance.However， during the process of coating preparation and service， the elements of the coating and substrate diffuse into each other.This diffusion alters the structure of the substrate phase， leading to the formation of an interdiffusion zone (IDZ) at the coating/substrate interface.It also results in the precipitation of the fine topologically close-packed phase (TCP)， rich in elements like Re， W， Cr，Mo， etc.The precipitation of the TCP phase weakens the solution strengthening effect， and as a brittle phase， it promotes the formation of cracks.Additionally， the formation of the IDZ reduces the bearing area of the substrate， leading to a decline in the high-temperature creep properties of the substrate.In this paper， the precipitation of the TCP phase and the formation mechanism of the IDZ of the coatings were described.Subsequently，the types of TCP phases (σ phase，μ phase，P phase)，their characteristics，and their harm to the performance of substrate were introduced.The primary methods to suppress TCP phase precipitation include adding platinum group modified elements and pre-depositing Ni layers.The additions of modified elements increase the solid solubility of solid solution elements， inhibiting TCP phase growth and nucleation， while the pre-deposited Ni layers reduce the diffusion of solid solution strengthening elements.Finally， it was expected that in the future， the precipitation TCP phase of aluminide coatings could be suppressed by adding multi-element modified elements and the combination of elemental modification and pre-deposition of Ni.

Keywords

• aluminide coating|element interdiffusion|topologically close-packed phase|modified elements|pre-depositing ni