In Search of Delayed Elasticity Prior to Fracture in a Nickel-base Single-crystal, CMSX-10

摘要

If delayed elasticity or the time dependent elastic effect in precipitation hardened polycrystalline nickel-base superalloys could be partly generated by the development of internal stressess, due to γ/γ′ interphase shearing processes, then single crystal (SX) superalloys must also exhibit delayed elasticity. To explore this, the delayed elastic effect in [001]-oriented CMSX-10 single crystals was investigated by long-term (near fracture) constant-load strain relaxation and recovery tests (SRRT) in the temperature range 800 to 1000℃ for an initial stress of 700 MPa and total strain of 15%. This high stress was used to avoid complications due to γ′ rafting. Small, but measurable delayed elastic strain of 0.0015, about 25% of the elastic strain, has been observed. The recovery times for delayed elastic strains were found to be significantly longer than the times under load. The γ/γ′interface cracking activities and their possible relationship with delayed elastic strain are discussed.