Inconel 718 合金之δ相於熱處理與熱機處理之析出研究

Abstract

Nickel-based superalloy Inconel 718 is largely used due to its good mechanical properties and good corrosion resistance. For gas turbine engine disks and shafts, fatigue resistance, particularly low cycle fatigue resistance, may in fact be the limiting factor in the establishment of the useful operating lives of such components. Ultra fine grain 718 has been developed for this application. Overaged δ phase which are stable above recrystallization temperature used as pinning phase during recrystallization. Studying on δ phase and choosing good parameter for thermal mechanical process are important for grain refining Inconel 718. The research work used optical microscopy and transmission electron microscopy to observe the precipitation and crystallography of δ phase precipitated during high temperature aging in Inconel 718. The orientation relationship between matrix (γ) and δ phase was determined by several diffraction patterns. TEM images shows that the growth of needle-shaped or plate δ phase was connected by periods of small part δ phase. δ. Some TEM observation shows that γ” crystal structure existed inside the needle-shape precipitation. The precipitation and growth of overaged δ phase associated with metastable γ” phase. Thermal process results shows Inconel 718 aged at 900˚C precipitate larger amount of δ phase than other aging temperature. Select two thermal process precipitating δ phase for thermal mechanical process. The results was that after 60% compression the δ phase broken as globular shape and has uniform distribution. The compression at 1100˚C has apparent recrystallization and all δ phase been solid solute; compression at 1025˚C shows some recrystallization and almost all δ phase been solid solute. At 900˚C no recrystallization occurs and δ phase conserve during compression. The work results providing the good thermal mechanical process temperature for ultra fine grain 718 was 980~990˚C. 60% compression for uniform distribution and globular δphase.