Compositionally Complex Alloy as Brazing Filler Metal for Joining Honeycomb Sealing Systems

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. Using transient liquid phase bonding processes with filler materials containing boron or silicon as melt-point depressants can introduce brittle phases in the microstructure due to eutectic solidification after an insufficient isothermal hold, leading to limited ductility and potentially compromising the overall mechanical properties and longevity of the brazed components. To address this challenge, a novel MnFeCoNiCu compositionally complex alloy (CCA) filler was implemented, targeting a face-centered cubic phase with no embrittling microconstituents in the braze.

In this study, the reference braze filler alloy selected for comparison to the CCA is the nickel-chromium-silicon filler metal BNi-5 (AMS 4782) on Haynes 214 as the base material. The CCA braze filler metal used in this work has an approximate composition of Mn₃₅Fe₅Co₂₀Ni₂₀Cu₂₀ (in at%). Considering the effects of high-temperature exposure on the microstructure of Haynes 214, the brazing parameters for the CCA filler on this substrate require independent optimization from those employed in prior work. To assist in this optimization, a novel in-situ contact angle measurement system was developed, allowing real-time analysis of the temperature and time-dependent contact angles at high temperatures and in various atmospheres. An analysis of the wetting kinetics of the CCA filler on Haynes 214 substrate was conducted to propose new brazing parameters that allow sufficient time to effectuate wetting while limiting the microstructural evolution of the Haynes 214 base material. Optimal results were achieved with brazing temperatures between 1140°C and 1200°C, rapid cooling rates exceeding 30°C/min, and a maximum holding time at brazing temperature of 100 minutes, all of which contribute to enhancing the mechanical properties of the composite.