Changes of γ′ precipitate characteristics in damaged superalloy IN738LC during different stages of rejuvenation heat treatment cycles

Abstract

The present study investigates the evolution of c9 precipitate microstructure in a creep damaged IN738LC superalloy during different stages of rejuvenation heat treatment cycles. Dissolution of coarsened c9 precipitates in the creep damaged alloy occurred during different solution treatments. The precipitates that did not dissolve completely during solution treatment and those formed during subsequent cooling were considered to be as remnant and cooling precipitates respectively. It was found that higher solution treatment temperatures result in lower volume fraction of remnant precipitates and further formation of cooling precipitates. Slower cooling rates after solution treatment gave the chance for the existing c9 particles to be coarser. Moreover, aging treatment increased the volume fraction of c9 precipitates. Double solution treatment at 1190uC/4 h/furnace coolingz1120uC/4 h/air cooling followed by aging at 845uC/24 h/air cooling dissolved nearly all the coarsened precipitates and produced a new bimodal c9 microstructure analogous with that of the original alloy.

Study of microstructure degradation and rejuvenation evolution for F-class gas turbine blade

“…– approximately 24,000 h) recommended by the manufacturer. The huge cost of replacement components has driven the development of refurbishing processes to recover the microstructure and properties of the blades [3,4].…”

Rejuvenation heat treatment's influence on the microstructure and properties of superalloys

“…By studying the creep behaviour of Nimonic 105, Girdwood and Evans [8] found that completed re-solution heat treatment could heal the creep damaged microstructure. Hosseini et al [9] compared the original, damaged and re-heat treatment of the IN738LC alloy, and found that coarsening γ′ and carbides in the MC type transforming area could be dissolved back into the matrix. However, the main concern of these studies is the evolution of damaged microstructure during heat treatment and lack of research on the effect of heat treatment parameters, especially the cooling rate.…”