Anisotropic Growth of the Primary Dendrite Arms in a Single‐Crystal Thin‐Walled Nickel‐Based Superalloy

Abstract

The influence of the withdrawal rate and wall thickness on the primary and secondary dendrite arm spacings of single‐crystal specimens manufactured by the Bridgman process is investigated. Thin‐walled specimens with wall thicknesses of 0.4, 0.8, 1, and 2 mm are compared with conventional cast single‐crystal cylindrical specimens with a diameter of 15 mm of the nickel‐based superalloy MAR M247LC. It is found that the average primary dendrite arm spacing decreases slightly with decreasing wall thickness, whereas the secondary dendrite arm spacing is relatively independent of the cast wall thickness. The slight decrease in primary dendrite arm spacing relates to an ≈ 0.2 mm wide boundary zone next to the ceramic mold/cast metal interface that is not only present in the thin‐walled specimens, but also within cylindrical single‐crystal specimens. Within this boundary zone, the primary dendrite arm spacing is anisotropic. While the spacing of two dendritic cores sitting aside each other (y‐direction) remains at the bulk value, the spacing of two dendritic cores sitting in line with the interface normal (x‐direction) is significantly reduced.

Effects of Preheating on Thermal Behavior in Inconel 718 Processed by Additive Manufacturing

“…When solidification initiates, it leads to the formation of dendrites, which exhibit a tree-like crystal structure [26]. The determination of the primary dendrite arm occurs when the surface normal is parallel to the growth direction, as shown in [27] (Figure 12). The primary dendritic arm spacing is defined as the distance from the center of the primary dendrite to the center of the nearest neighboring primary dendrite [28].…”

“…The primary dendritic arm spacing is defined as the distance from the center of the primary dendrite to the center of the nearest neighboring primary dendrite [28]. The secondary dendrite arm spacing is determined when the surface normal is perpendicular to the growth direction [27] (Figure 12). When solidification initiates, it leads to the formation of dendrites, which exhibit a tree-like crystal structure [26].…”

Effect of Wall Thickness and Surface Conditions on Creep Behavior of a Single-Crystal Ni-Based Superalloy

“…Thin-walled single-crystal specimens with wall thicknesses of 0.4, 0.8, 1.0 and 2.0 mm were cast. Detailed investigations of the as-cast dendritic structure of these thin-cast specimens were already published [20]. Casting geometry is shown in Figure 1 and consisted of two thin-walled windows (30 × 8 mm 2 ), having wall thicknesses of 0.4, 0.8, 1.0 or 2.0 mm, respectively.…”

Lattice Rotation and Deformation Mechanisms under Tensile Loading in a Single-Crystal Superalloy with [001] Misorientation

“…However, during the actual casting process of the blades, due to factors such as alloy properties, processing conditions, and casting structure, it is difficult to ensure that the principal stress axis of the blade is perfectly aligned with the [001] orientation of the single crystal, often resulting in deviations. As turbine inlet temperatures increase and single-crystal superalloys evolve, the incorporation of more refractory elements characterized by low diffusion coefficients complicates the control of the crystal orientation of single-crystal blades [ 4 , 17 , 18 ]. In practical engineering applications, blades that deviate from the [001] orientation by up to 15° are generally considered acceptable, reflecting a compromise between casting difficulties and performance requirements.…”