Creep properties of a Pt-aluminide coating

The tensile creep properties of a β-rich (Ni,Pt)Al diffusion coating have been determined at various strains over the temperature range 800-1000 °C by deconvoluting the creep response of layered composite specimens under constant stress conditions. It is found that the creep strength of the diffusion coating tends to be higher than that of a similar coating tested previously by Pan et al. [Pan D, Chen MW, Wright PK, Hemker KJ. Acta Mater 2003;51:2205]. Associated with the higher strength is a relatively high creep activation energy (∼600 kJ/mol) and a high stress dependence of creep rate which increases with creep strain from ∼6.8 at 1% strain to ∼9.4 at 9% strain. These high values and the associated high creep strength are attributed to the formation, at the creep temperatures, of a fine dispersion of second-phase particles, presumed to be γ′ and possibly α-Cr, within the β-(Ni,Pt)Al matrix. It is suggested that the extent of this transformation and, hence, the strengthening effect are related to the original aluminium and platinum content of the coating.