Anisotropy of high cycle fatigue behavior of a Ni-base single crystal superalloy

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.