Thickness Influence on the Creep Response of DD6 Ni-Based Single-Crystal Superalloy

Abstract

The effect of specimen thickness on the creep response of Ni-based single-crystal superalloy DD6 was investigated. With the thickness of 0.3 mm, 0.6 mm and 1.2 mm, a series of thin-wall specimens were tested in this paper respectively at 760℃, 980℃ and 1,100℃. Under the conditions of lower temperatures and higher stresses, the creep life of thin-wall specimens increases with the increase of δ, but it is almost equal under higher temperatures and lower stresses conditions. Compared with the standard specimens, an obvious reduction (about 60%) of creep life of the thin-wall specimens was found at 760℃, whereas it is almost the same at 980℃ and 1,100℃. Therefore, obvious thickness effect is prone to lower temperature and higher stress. The thickness effect is a comprehensive effect, which is caused by fracture mode, the degree of necking, the shape and quantity of creep cavities, oxide thickness, etc. Under each condition, an increased thickness resulted in increased creep strain to rupture.

Tensile creep of miniaturized specimens

“…Seetharaman and Cetel 23 additionally mention the differences in deformation constraint and plastic anisotropy between the thick and thin sections and obtain a limit for the thickness debit which is around 4 mm. Mälzer et al 6 (LEK94) use specimens with a 2 Â 2 mm 2 gauge section and obtain results in reasonable agreement with results from standard specimens, whereas Wen et al 24 (DD6) observe results similar to conventional specimens at a thickness of 1.2 mm. Gibbons 22 obtains creep cavitation as the responsible failure mechanism for Nimonic-90 and states 1 mm thickness as the limit for the decrease in creep performance.…”

A thickness‐sensitive and orientation‐related creep lifetime prediction method of nickel‐based single crystal superalloy

“…The creep lifetime prediction results of DD6 specimens based on Miner's linear damage accumulating theory (760°C and 980°C) 26 . [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…However, according to the investigation in Ref. [26], nickel‐based single crystal superalloy DD6 has obvious abnormal thickness debit effect at 1100°C. In this paper, the abnormal thickness debit effect is considered to be caused by the larger damage of zone 2 at 1100°C.…”

“…In terms of thickness debit effect investigation of nickel‐based single crystal superalloy, a large number of researches about nickel‐based single crystal specimens indicate that the decrease of thickness generally results in the reduction of creep lifetimes 8–11,26–31 . Doner et al 9 found that there was obvious thickness debit effect for the nickel‐based single crystal superalloy CMSX‐3 specimens tested in air, while almost no thickness debit effect was found for both aluminide coated specimens tested in air and uncoated specimens tested in high‐purity argon, which indicated that the thickness debit effect of CMSX‐3 was primarily due to environmental effects.…”

Oxidation Behavior of the Nickel-Based Superalloy DZ125 at 980 °C

“…When the superalloy operates at oxidation circumstance, on the one hand, the oxide morphology on the surface and the oxide growth process can destroy the microstructure integrality, especially change the strengthening phase morphology [3]. Then, it causes a mechanical properties gradient from the surface to the bulk materials which has a very weak creep resistance [4][5][6][7]; on the other hand, the oxides itself are inherently brittle materials inducing crack initiation and therefore reducing turbine component creep life [8][9][10][11]. Therefore, high-temperature oxidation mechanism of nickel-based superalloys plays an important role in optimizing the design and durability analysis of turbine blade.…”