Changes in the structure and dislocation substructure of alloy EI437B during creep

Heat treatment of the EI437B alloy consisted of annealing for 8 hr at 1080°C and quenching by cooling in air (at a rate 100 deg/min), followed by ageing at 700-800°C. Some specimens were aged using low-temperature ageing (LA) for 16 hr at 700°C. The others were aged for 10 hr at 700°C+2 hr at 800°C - (LA+HA, HA - high-temperature ageing). This treatment was chosen because the mechanical properties and long-time strength of alloy EI437B are enhanced appreciably by staged ageing. Creep tests were done at 700°C, load σ=450 MPa. The change in dislocation structure and interaction between particles and dislocations during creep was studied after holding for different times (τ, hr): 4, 20, 40, 90, 95 and 146 hr, and after fracture. The mechanisms of interaction of gliding dislocations and γ′-phase particles at different stages of creep are established.