Influence of Aging Heat Treatment on Creep Strength of CMSX4
Koji KAKEHI and Satoru TAKAHASHI
Abstract:In single crystals of Ni-based superalloys, the ƒÁ' precipitate size has been shown to affect both the tensile strength and the creep behavior at intermediate temperatures. The microstructure of Ni-based superalloys contains primary cuboidal ƒÁ' particles that precipitate during aging treatment, and cooling ƒÁ' particles that precipitate during cooling from the aging temperature. In the Ni-based superalloy containing a high volume fraction of ƒÁ' precipitates, the change in the morphology of the secondary ƒÁ' precipitates in a matrix channel has been found to affect the creep strength. In this study, three kinds of aged specimens were prepared to investigate the influence of the morphology of ƒÁ' precipitates on the strengths of CMSX4 alloy. Slow furnace cooling from the aging temperature was employed to obtain a clean matrix channel completely devoid of secondary ƒÁ' precipitates. In order to clarify the effect of secondary ƒÁ' precipitates, the strengths of the furnace-cooled specimens were compared with those of the forced-air-quenched specimens containing numerous superfine ƒÁ' precipitates in the matrix channel, and those of the standard two-step-aged specimens. The purpose of the present investigation is to gain a better understanding of the effect of precipitation heat treatment on the material strengths at an intermediate temperature, where the secondary ƒÁ' precipitates remain undissolved during creep deformation. Key Words:Superalloy, Single crystal, CMSX4, Aging heat treatment, Crystallographic orientations, Secondary precipitates, Creep strength