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Tensile behavior of the nickel-base single-crystal superalloy DD6 was studied from room temperature to 1020 °C. The plate specimens were along [001] orientation parallel to the loading axis in tension. The microstructures on the surface and fracture morphology were investigated after tensile test to rupture by scanning electron microscopy (SEM). The results of the present investigation indicate that the yield strength at 650 °C is superior to that at room temperature, 850 °C and 1020 °C. Low ductility and serrated flow in stress–strain curves were also observed at 650 °C. The microstructures on the surface of the plate specimens and fracture morphology observation indicated that localized slip which resulted in glide plane decohesion caused the low ductility of DD6 alloy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Aluminizing treatment decreased the creep strength of superalloy. [•] Long-term exposure deteriorated the creep strength of coated superalloy. [•] Surface orientation affected the creep lifetime of coated superalloy. [•] Fracture deformation mechanism in coated superalloy was discussed. [Copyright &y& Elsevier]

Abstract: By means of the stress–strain finite element method (FEM) in elastic–plastic regime, the influences of the applied stress on the distribution of von Mises stress and evolution of shape regularity of γ′ phase in a [011] oriented single crystal nickel-based superalloy are investigated. Results show that, after full heat treatment, the microstructure of [011] oriented single crystal superalloy consists of the cuboidal γ′ phase embedded coherently in the γ matrix phase, and on (100) plane aligned regularly at angle of 45° relative to the [011] orientation. During compressive creep, the cuboidal γ′ phase is transformed into the mesh-like lamellar rafted structure on (100) plane. Therefore, the changes of the lattice strain, the strain energy density and interfacial energy are thought to be the driving forces of the element diffusion and γ′ phase directional growth. During compressive creep, the lattice contraction occurs on (100) plane of the cuboidal γ′ phase along [001] and [010] directions, whose extruding effect may repel Al, Ti atoms with bigger radius. Therefore, the expanding strain of lattices along [100] direction on (010) and (001) planes of the cuboidal γ′ phase may trap Al, Ti atoms to promote the directional growth of γ′ phase on (100) plane along [001] and [010] directions, which is thought to be the main reason for the γ′ phase growing directionally into the mesh-like lamellar structure. [Copyright &y& Elsevier]

Abstract: The rotary bending high cycle fatigue properties of a single crystal superalloy in three orientations were tested at 700°C in ambient atmosphere. The [011] orientation shows the highest fatigue strength. Moreover, the fatigue strength with 〈111〉 orientation is obviously higher than that with 〈001〉 orientation. There are two types of fracture modes, one is cleavage fracture for the [001] orientation, the other is the mixed fracture of cleavage and tearing for the [011] orientation. The 〈011〉 orientation shows more pronounced crystal lattice rotation than the 〈111〉 orientation. Nevertheless, lattice rotation does not occur in the crystals with [001] orientation. Fatigue steps of the [001] and [111] orientated crystals propagate along different {111} glide planes, which means that the slip in 〈111〉 orientation moves more easily than in 〈011〉 orientation. The typical deformation mode of [001], [011] or [111] orientation is respectively slip bands running through γ and γ′ phases, dislocation pairs shearing γ′ particles, or superlattice stacking faults besides high-density dislocation shearing γ′ particles. [Copyright &y& Elsevier]