70 巻 (2006) 1 号 p. 47-50
Ni-base superalloys require a multi-step heat-treatment to be used in practice, which includes solution heat-treatment and 2 step aging. The size and form of the γ′ precipitates, which strengthen the superalloys, strongly depend on the first step aging condition. A relationship exists between the sizes of the γ′ precipitates and creep strengths, which exhibits a creep condition dependence. In this paper, the effects of the first step aging condition on the size and the form of γ′ precipitates and creep strengths are examined for TMS-26, a first generation Ni-base single crystal superalloy. The results showed that, in 1100°C-137 MPa creep, the initial microstructure should be kept in coherency for increased creep strengths. On the other hand, in 900°C-392 MPa creep, a relatively high first step aging temperature was found to be effective for increasing creep strengths. It was concluded that increasing the first step aging temperature is effective for the improvement of creep strengths, given that coherency is kept in the initial microstructure.