Direct assessment of the creep strength of DS cast turbine blades using miniature creep specimens

The present paper presents a novel approach which allows a direct assessmen t of the creep strength of thin walled DS turbine blades at temperatures up to 1100 degrees C using a grain morphology sensitive miniature creep speci men test technique. The work builds up on earlier investigations by DeMestr al and co-workers ([i] B. DeMestral et al., Met. and Mat. Transactions A, 2 7A (1996) pp. 879-890 and [ii] B. DeMestral and G. Eggeler, Prakt. Metallog r., 29 (1992) pp. 174-191) on the influence of grain morphology on creep de formation and damage accumulation in superalloys with elongated macrograins . The paper reports the important features of this new procedure which incl ude (i) the creep test technique (specimen geometry and grip design) and (i i) the removal of creep specimens from a DS CM 247 LC cast blade with respe ct to the morphology of the macrograins. The paper also reports creep resul ts obtained with this new technique at temperature of 1030 degrees C and a tensile stress of 180 MPa and discusses the results on the basis of the ass ociated microstructural creep deformation and damage mechanisms.