Nanoindentations as a local probe for the mechanical properties and alloying influences in nickel-base superalloys and aluminide coatings

Abstract

Nanoindentation techniques have been applied to study the local mechanical properties of the three commercial single-crystalline nickel-base superalloys CMSX-6, CMSX-4 and CMSX-10 which have an increasing amount of rhenium and tungsten as well as to study the local mechanical properties of two platinum modified aluminide coatings, one having a single-phase NiAl structure and the other having a two-phase NiAl / PtAl2 structure, in the ascoated condition and after thermo-mechanical fatigue testing. It was found, that the hardness of the γ-matrix in superalloys increases with the concentration of refractory elements, whereas only a small change in the hardness of the precipitates was found. The local mechanical properties of the coatings showed a strong correlation between aluminium concentration and structure on one hand and hardness and Young's modulus on the other hand. It was found that the hardness of the single-phase aluminide phase within the coating increases with decreasing aluminium concentration, whereas the modulus decreases. Furthermore, it was found that the two-phase coating has a very high hardness in the as-coated condition, which decreases significantly after TMF-cycle due to the dissolving PtAl2-phase.