Precipitation behavior of γ′ phase in P/M superalloy Udimet720Li

Abstract

P/M superalloy Udimet720Li specimens were solutioned and quenched at the different cooling rates in gas quenching furnace, following by the double aging treatment. The microstructures and elevated temperature tensile properties at 650 ℃ were investigated, and the γ′ precipitation behavior and strengthening mechanism were analysed. The effect of cooling rates on the microstructures and properties of γ′ phase were discussed. Results show that the secondary γ′ phases mainly precipitate between 900 ℃ and 1000 ℃ for the P/M superalloy Udimet720Li, and the size of the secondary γ′ phases are inversely proportional to the cooling rates. The secondary γ′ phase interacts with the dislocations by shearing mechanism, enhancing the strength of P/M superalloy Udimet720Li. The strengthening effect increases with the decrease of the secondary γ′ phase size. To meet the strength requirement in practical application, the cooling rate should be more than 100 ℃/min. Therefore, the recommended solution cooling path for P/M superalloy Udimet720Li is shown as follow: the cooling rate should be slow to reduce the quenching stress above 1000 ℃, then the specimen can be quenched in oil at 1000 ℃ to obtain enough strength.

Keywords

• p/m superalloy
• cooling rate
• strengthening phase
• mechanical property
• solution treatment