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The present paper presents a novel approach which allows a direct assessment of the creep strength of thin walled DS turbine blades at temperatures up to 1100 °C using a grain morphology sensitive miniature creep specimen test technique. The work builds up on earlier investigations by DeMestral and co‐workers ([i] B. DeMestral et al., Met. and Mat. Transactions A, 27A (1996) pp. 879–890 and [ii] B. DeMestral and G. Eggeler, Prakt. Metallogr., 29 (1992) pp. 174–191) on the influence of grain morphology on creep deformation and damage accumulation in superalloys with elongated macrograins. The paper reports the important features of this new procedure which include (i) the creep test technique (specimen geometry and grip design) and (ii) the removal of creep specimens from a DS CM 247 LC cast blade with respect to the morphology of the macrograins. The paper also reports creep results obtained with this new technique at temperature of 1030 °C and a tensile stress of 180 MPa and discusses the results on the basis of the associated microstructural creep deformation and damage mechanisms.

The objective of the present paper was to show the various macro-lmicrostructural appearances of the ODs materials MA 956 and PM 2000 at the surface and in the bulk after exposure to high temperatures in combustion chambers (gaseous environment). At the surface a chromium oxide layer forms above the alumina layer originally formed after preoxidation. At locations where the surface has been melted these two oxide layers disappear and an iron oxide showing cracks forms at the surface. Several cracks run into the material. In the bulk material due to high thermal gradients a porosity of up to 18 % in MA 956 and 2% in PM 2000 develops during operation (Kirkendall effect). With longer operation times, at higher temperatures and probably in other environments (chemical cracking of the fuel) internal oxidation or nidriding of aluminium andlor formation of chromium carbides take place.