Highly non-linear creep life induced by a short close γ′-solvus overheating and a prior microstructure degradation on a nickel-based single crystal superalloy

Abstract

Specific non-isothermal creep conditions were applied to a 1st generation single crystal nickel based superalloy at very high temperature. Creep tests were conducted under 120 and 160MPa at 1050°C with one overheating under stress at 1200°C for 30s. Results were compared to the ones already obtained under 140MPa on the same alloy as well as on a fourth generation of alloy.It is shown that the residual creep life after a single overheating is optimal after a specific prior-creep time. The impact of the creep degradation prior to an overheating on the creep life is dependent on the magnitude of the effective γ/γ′ lattice mismatch. Indeed, an overheating performed when the effective γ/γ′ mismatch magnitude is maximum leads to longer creep lives, even better than without overheating.