Heat-treatment of GH2747 superalloy and the strength–toughness balance
GH2747 is a γ′-strengthened wrought Fe–Ni–Cr superalloy designed for service up to 1 250 °C (short-term 1 300 °C). Its heat-treatment protocol is built around three precisely controlled stages:
Solution treatment 1 100–1 200 °C for 1–2 h (time adjusted to section thickness), water quench. • Fully dissolves γ′ (Ni₃Al) and carbides, creating a homogeneous austenitic matrix. • Temperatures above 1 220 °C or dwells longer than 2 h promote abnormal grain growth and must be avoided.
Intermediate anneal (optional after heavy forming) 900–950 °C for 1 h, furnace cool. • Relieves cold-work stresses, prevents quench cracking and improves dimensional stability.
Two-step ageing • Stage I: 760–800 °C / 4–6 h, air cool → nucleates a fine γ′ precipitate. • Stage II: 650–700 °C / 10–12 h, air cool → refines and stabilises γ′ to a mean size of 50–100 nm.
Strength–toughness optimisation
Grain size • Keep solution temperature ≤ 1 200 °C to maintain a fine grain structure (ASTM 5–6), which raises impact toughness without sacrificing creep strength.
γ′ precipitation • Strength-oriented: extend Stage I time or slightly raise temperature to increase γ′ volume fraction.
• Toughness-oriented: lower Stage II temperature to 640–660 °C (or shorten time) to suppress γ′ coarsening and avoid continuous M₂₃C₆ films at grain boundaries.
Boundary chemistry Reducing the final ageing temperature also suppresses Cr- and W-rich carbide films, enhancing intergranular ductility.
By fine-tuning solution parameters and ageing cycles, GH2747 can be tailored to deliver the required balance between high-temperature strength and fracture toughness for demanding aerospace and energy applications.
