ニッケル基超合金単結晶の再結晶挙動

抄録

Single crystal turbin blades made of nickel-base superalloys hawe been frequently employed for modern air-craft engines. It was reported that recrystallization could take place during solution heat-treatment at highly strained parts of castings due to solidification constractions or at parts where various cold works were given. It was also observed that there were in differences susceptibility to the recrystallization among single crystal alloys. In the present study, the reduction of creep strength due to recrystallization was measured using single crystal samples (Alloy 454, TMS26) with intentionally induced recrystallized layers to various depths, and, the susceptibility dependence on the alloys (CMSX-2, TMS12-2, TMS26) was examined by reheating samples after tensile tests. The following conclusions were obtained.
(1) The recrystallization took place in all of the alloys at temperatures above 1273 K.
(2) The degree of the reduction of the creep rupture strength was related to the reduction of the load-bearing cross-sectional area due to recrystallization.
(3) When the reheating temperature was between 1273 K and γ′ solvus of the alloy, the grain size of the recrystallized parts was small (<0.1 mm). However, when the temperature exceeded the γ′ solvus, the abnormal grain growth took place and the sample ruptured instanteneously.