Abnormal Grain Growth During Rapid Annealing of Sol–Gel Alumina Thin Film Deposited on Ni‐Based Superalloy

Abstract

A ∼50 nm thick alumina layer was deposited on an Ni‐based superalloy substrate by a sol–gel method. α‐AlOOH particles presented in the layer after drying at 140°C transformed mostly to α‐Al2O3 grains within ∼1 min at 1100°C under a low oxygen partial pressure annealing environment. During the same time period, the α‐Al2O3 grains grew significantly in the lateral direction, resulting in the aspect ratio of grain diameter to thickness of ∼20. The presence of a preferred orientation in the α‐Al2O3 layer suggested that the mechanism for the lateral growth was abnormal. The lateral growth mechanism appeared to become very slow when a critical thickness (∼100 nm) was reached.