Creep deformation behavior and failure diagnostic diagrams of a columnar-grained nickel-based superalloy

Uniaxial creep deformation of a columnar-grained cast Ni-based superalloy has been analyzed in the temperature range of 1035-1315 K. Two-stage heat treatment of the material resulted in an average γ′ particle size of 0.4 μm and inter-particle distance of 0.04 μm. At 1035 K, the alloy showed predominantly primary creep with very low tertiary creep strains. At temperatures above 1035 K, a pseudo-tertiary creep regimen is predominant. Faceted fracture, coarsening of γ′ particles, decohesion of the matrix around the particles, and rafting of the coarsened γ′ particles have been observed as failure modes over the temperature range studied. An analysis is presented to understand creep deformation behavior of the material in the secondary and tertiary creep stages, by expressing them as power functions of time. Failure diagnostic diagrams have also been constructed for the material over the temperature range investigated.