Research on the relationship between high-temperature stress relaxation and creep of directionally solidified nickel-based superalloy by small specimen testing

Preparing standard high-temperature mechanical test specimens is difficult for components with complex geometries or special structures. Small specimen testing is promising for low material consumption and minor damage, yet the relaxation-creep correlation between small and standard specimens and underlying key parameter mechanisms remain unclear.Herein, comparative creep rupture and stress relaxation tests were performed on small and standard DSDL directionally solidified nickel-based superalloy specimens to investigate effects of loading rate and pre-strain on their relaxation-creep responses.Results show pre-strain ≥5% enables small specimens to rapidly enter the steady-state relaxation stage. Loading strain rate affects initial relaxation-creep rate but negligibly influences the stress-dependent steady-state rate within 0.0001–0.0002 s⁻¹. Creep activation energy Q and stress exponent n reveal creep behaviour distinctions and governing mechanisms. Rupture tests yield similar curves; small specimens have a higher minimum creep rate but comparable rupture time.