Honeycomb sealing systems are used in aircraft turbines to minimize airflow leakage in the gaps between rotating parts and the turbine casing. The minimized airflow leakage improves the efficiency of turbines which leads to a reduction of carbon dioxide emissions [1]. Another important task of the honeycomb sealing system is to protect the fins of the rotating turbine blades from critical damage when a contact, caused by thermal and mechanical expansion, occurs [2]. This is achieved by controlled wear of the honeycomb seals.

Honeycomb seals are manufactured by brazing a hollow honeycomb structure made from nickel-based superalloys onto a carrier plate. During this brazing step the braze filler rises to the contact surface with the rotor fin due to capillary forces [3]. Therefore, it is of particular interest to examine the mechanical properties of the base material, the braze filler alloy and the interdiffusion zones when investigating the rubbing behavior of honeycomb sealing systems.

In this work Haynes 214 metal sheets after brazing with the nickel-chromium-silicon braze filler BNi-5 (71 wt.% Ni, 19 wt.% Cr, 10 wt.% Si) are investigated. Ultra-high strain rate deformation of the brazed metal sheet composite at temperatures up to 1100°C is studied. Microstructural examinations are performed using scanning electron microscope, energy-dispersive X-ray spectroscopy, electron backscattered diffraction and X-ray diffraction.

Interdiffusion zones and hard phases with increased amounts of chromium or silicon are observed along the brazed joint region. For the brazed metal sheet composite decreased ductility with increased brazed joint thickness is found. We present tensile data with strain rates up to 50 s-1. With the experimental investigations the fundamental understanding of the rubbing process of honeycomb seals is improved.

References

[1] H. L. Stocker, D.M. Cox and G.F. Holle NASA Report, 1977, No. NASA-CR-135307.

[2] D. Sporer and D. Fortuna Welding Journal, 2014, Volume 93(2),44–48.

[3] S. Ulan kyzy, R. Völkl, O. Munz, T. Fischer and U. Glatzel J Mater Eng Perform, 2019, Volume 28(4), 1909-1913.