Corrosion behaviour of NiCrFeAl‐hBN seal coatings in oxidation environments at a high temperature

Abstract

Abstract The purpose of this investigation was to evaluate the microstructure, high‐temperature oxidation behaviour, and hardness of a seal coating under controlled exposures at 750 °C with different exposure times. The results reveal that the main phases in the coating are Ni, FeNi 3 , and hexagonal BN, with α‐Al 2 O 3 peaks appearing after 2‐h oxidation. As the exposure time increases, the diffraction peak intensity of α‐Al 2 O 3 begins to decrease and Cr 2 O 3 peaks appear after 200 h. After 1000 h, Cr 2 O 3 becomes dominant with only small amounts of α‐Al 2 O 3 remaining. The high‐temperature oxidation process of the coating includes three stages: the fast stage, transition stage, and slow stage. The oxidation rate is constant in each stage, and in the fast stage and slow stages with values of 7.59 × 10 −4 and 8.37 × 10 −5 mg 2 ·cm −4 ·s −1 , respectively. Initially, α‐Al 2 O 3 forms near the pores in the coating, followed by the formation of Cr 2 O 3 . As the exposure time increases, oxidation penetrates into the interior of the coating along phase boundaries to form island‐shaped inner oxide layers with high concentrations of Cr, Ni, and Fe. Additionally, hardness increases with increasing oxide percentage.