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Creep behavior of the single crystal nickel-base superalloy René N5 is investigated as a function of material thickness. The results point out that reducing the thickness from 1.0 to 0.2 mm leads to both shorter creep lives and much higher overall creep strain rates of thin specimens. The orientation of the specimen is an important factor too but has a weaker influence on creep behavior under the given test conditions than the specimen thickness. IntroductionSingle crystal nickel-base superalloys are used in blades and vanes of stationary gas turbines and aero engines. Their lifetimes are mainly limited by fatigue, creep and hot corrosion at elevated service temperatures. To increase lifetime a possible strategy is to reduce the material temperature by cooling. In order to optimize both the cooling efficiency and the weight of fast rotating turbine blades a general trend is to reduce the wall thickness of the hollow investment casting parts. The relation between creep properties and section thickness was rarely investigated [1][2][3][4][5][6][7][8][9][10]. For the polycrystalline nickel-base superalloy PWA 1484 Duhl [1] found a five fold reduction of creep rupture life if the specimen thickness is diminishing from 4 to 0.5 mm which mainly depends on grain size and micro structural defects. Doner and Heckler [3,4] observed in uncoated single crystal CMSX-3 a 30% loss in creep rupture life if the wall thickness was reduced from 3.18 to 0.76 mm at 982°C and if the stress level was below 275 MPa. They also found that the time to reach 1% strain was unaffected by wall thickness at a constant stress level. Seetharaman and Cetel [6] reported similar results for single crystal PWA 1484 with wall thicknesses of 1.76 and 0.38 mm respectively and stresses below 275 MPa at 982°C. They concluded that oxidation and the more constrained plastic deformation are the major contributions for early failure of thin specimens. Doner and Heckler [3,4] found that creep rupture properties of aluminized nickel-base superalloys are less influenced by the specimen thickness. By contrast Seetharaman and Cetel [6] mentioned a loss of creep rupture lifetime of 30-40% with a thickness reduction from 1.52 to 0.25 mm for coated Knowledge and understanding of the creep behavior is a fundamental prerequisite for component life-time predictions. Therefore the effect of thickness reduction on the creep properties of uncoated and aluminized single crystal nickel-base superalloy René N5 is investigated in this study. In addition deviations from the [001] orientation are incorporated into this study which is part of a ongoing research carried out for the next years.

Some materials for turbine applications show volume contraction during service lifetime. Relative shrinkage (Dl/l 0 ) of up to about À4 Á 10 À4 may occur. In this study Waspaloy samples were exposed up to 10 000 h at 550°C, 650°C and 750°C. High resolution length measurements unveil remarkable contraction during exposure at 550°C and 650°C and less contraction at 750°C. The main contribution to sample contraction is compositional variation due to temperature dependent phase fraction changes. Lattice parameters of matrix and g 0 phase decrease within the first 300 h of temperature exposure. In addition carbide transformation from TiC to Cr 23 C 6 contributes to the observed contraction.

The airfoil alloy IN 939 has been evaluated for the use in large aircraft engine structures. Castability trials, including sprayforming, structural welding, with electron beam (EB) and with laser, as well as repair with TIG-welding have been performed. Brazing has also been evaluated while different heat treatment schedules for pre-and post-welding and for the solution and age cycle were reviewed. Mechanical property data, tensile, creep, LCF, FCG, were established for several temperatures on material excised from large castings and on weldments. The performance of the sprayformed (SF) material was superior to the conventionally cast (CC) material but notchsensitivity was noticed in creep testing.