Tertiary Creep in the Cast Nickelbase Superalloy IN738LC. Effects of Pretreatments

Abstract

A composite model proposed for the description of tertiary creep in structures containing a high volume fraction of reasonably large second phase particles has been successfully applied to creep data for IN738LC. Two batches of IN738LC and four different pretreatments have been successfully analysed with the model. The two batches displayed quite different particle growth kinetics and developed different morphologies. Both of these differences were consistent with a difference in particle/matrix misfit between the two batches. The increase in creep rate at elevated temperature following predeformation at ambient temperature may be explained by the same model. At low temperatures dislocations are generated within the particles due to the relatively low strength of the particles in relation to the matrix. These dislocations may then aid particle deformation at the elevated temperature thus causing the increased creep rate. © 1990, Walter de Gruyter. All rights reserved.