Influence of Crystal Orientation on the History Dependence of Primary Dendrite Arm Spacing in Ni-Based Single-Crystal Superalloy

Using a liquid metal cooling (LMC) high-gradient directional solidification furnace, this study compared primary dendrite arm spacing (PDAS) for nominal <001> deviation groups of 0°, 20°, and 45° under constant withdrawal rates and rate transitions between 15 and 100 μm/s. History dependence was evaluated by comparing the post-transition steady-region PDAS with the constant-rate reference at the same nominal current condition and normalizing the difference by the axial standard deviation of that reference. Under constant-rate growth, 30 mm was used as a common practical boundary for the relatively stable region. At 15 μm/s, steady-region PDAS increased from 182.1 ± 2.7 μm at 0° to 204.9 ± 2.7 μm at 20° and 259.2 ± 2.5 μm at 45°. At 100 μm/s, both misoriented groups remained above the 0° value, but the ordering of 20° and 45° was not monotonic. The rate-transition effect exceeded the axial reference variability for the 0° group at both target rates, whereas the effects for the nominal 20° and 45° groups remained within that variability. The observed morphologies are consistent with orientation-dependent trunk replacement by higher-order branching. These results show that crystal orientation and process path should be considered jointly when controlling PDAS.