Effect Of Specimen Thickness On The Creep Rupture Strength Of DD6 Superalloy

Since single crystal Superalloy has excellent high temperature properties, oxidation resistance and corrosion resistance, it had become the main materials of advanced Aero-Engine and gas turbine blades. The thrust-weight ratio and the turbine inlet temperature increased gradually with the development of the aerospace industry at home and abroad, and the gas-cooled blade structures become thinner and more complex, resulting in so-called thin-wall effect. Therefore, explore the effort of specimen thickness on the creep rupture strength of DD6 superalloy is of great importance and will provide a strong basis to predict the use status and life of engine blade.The DD6 nickel base single crystal Superalloy used in this article is provided by Beijing Institute of Aeronautical Materials, which is a kind of second generation single crystal superalloy self-developed by our country. Compared with the second generation of single crystal Superalloy abroad, DD6 has more excellent high temperature stress rupture properties. Under the condition of 980 ?/250MPa, the creep rupture life of 0.67mm,0.8 Imm and 1.12mm sheet samples is 185h,217.5h and 229h respectively.Microscopic observation was carried out on the blade and the bar, comparing their dendrite space and the shape and size of strengthening phase, combined with their microhardness, to make sure if the stress rupture property of the bar can represent the data of the blade. The result shows that their macroscopic pattern is consist of dendritic structure and their microstructure is consist of y phase and y'phase, no significant difference between them.By comparing the creep rupture life of different thickness of DD6 single crystal Superalloy at 980?/250MPa, combined with the scanning electron microscope, XRD, EDS, electron probe test to observe the morphology and analyze the composition of the fraction, cross section near the fraction and the longitudinal section to explore if the DD6 alloy has wall thickness effort and analyze the fracture mechanism. Results showed that the thickness effect of DD6 NI-base single crystal Superalloy is not obvious, with the reduction of the wall thickness, the creep rupture life decreased slightly. The fracture mechanism is mixed fracture consist of ductile fracture and brittle fracture. Presence of oxide film on the surface of the sample decreases the cross-sectional area of the specimen, thereby increasing the effective stress, and the micro-cracks in the longitudinal section of the sample and casting micro-holes initiated in the subsurface and the interior of the specimen result in the fracture. The fracture of thin wall specimen is coalescence of "surface oxidation-crack initiating-crack growth" and "inside creep damage". In the relationship between "surface oxidation-crack initiating-crack growth" and "inside creep damage", the more inside creep damage, the less thickness effect; Similarly, the role of surface oxidation — crack initiating-crack growth is big, the more thickness effect.