Effects of Brazing on the Oxidation Behavior of Honeycomb Seal Material Haynes 214

Honeycomb abradable sealing systems have a significant impact on the efficiency of gas turbines. The honeycomb seals are manufactured by brazing a corrugated hexagon metal sheet structure made from nickel-based superalloys onto a carrier plate. Often overlooked is the effect of the braze filler metal on the oxidation and the mechanical behavior of the honeycomb.

Therefore, the oxidation behavior of the honeycomb seal material Haynes 214 brazed with the nickel-chromium-silicon braze filler BNi-5 (71 wt.% Ni, 19 wt.% Cr, 10 wt.% Si) is investigated. Thermogravimetric analysis (TGA) is conducted for 24 h at 1000°C in an oxidizing atmosphere in order to determine isothermal oxidation kinetics. For cyclic oxidation testing, samples are exposed to 10 thermal cycles between room temperature and 1000°C giving a total exposure period of 1680 hours. Tensile properties are tested at temperatures of up to 1100°C. Microstructural examinations are performed using scanning electron microscope, energy-dispersive X-ray spectroscopy, electron backscattered diffraction and X-ray diffraction.

During oxidation particles of chromium-rich phases along the brazed joint dissolve, whereas particles of aluminum nitride phase precipitate. Additionally, thicker oxide scales are observed for the brazed metal sheets compared to pure Haynes 214 metal sheets. Elongation to failure of tensile tested brazed metal sheets increases with increasing oxidation time.