The Effect of Brazing on Microstructure of Honeycomb Liner Material Hastelloy X

Labyrinth seals with abradable metallic honeycomb structures are common in gas turbines to ensure a tight sealing between rotor and stator. These seals have a big impact on the turbine efficiency. The honeycombs made from nickel-based superalloys are brazed onto backing segments in order to form liners. In this work, the microstructure of Hastelloy X honeycombs after brazing with a nickel-chromium-silicon braze filler alloy is investigated. It was found that the braze filler can wet the honeycomb foils over their entire height up to the contact surface with the rotor. After solidification, the braze filler alloy forms γ and silicides (NiSi and Ni_y(Mo, Cr)_xSi). The intermetallic silicides give high hardness to the honeycomb liners. Between the braze filler alloy and the honeycomb foils, interdiffusion zones are observed. For the rub-in behavior of the honeycomb liners, not only the foil material but also the comportment of the composite made up of the foil material, the braze filler material and the interdiffusion zones has to be considered.