Rub-in processes in turbines - experimental investigation and modeling

• Applicants: Professor Dr.-Ing. Hans-Jörg Bauer; Professor Dr.-Ing. Uwe Glatzel; Professor Dr. Ewald Werner
• Subject Area: Hydraulic and Turbo Engines and Piston Engines ; Glass, Ceramics and Derived Composites ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2015 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 268769401

• Final Report Year: 2024

Final Report Abstract

In the present DFG project, the influence of the manufacturing process of honeycomb seals on the rubbing behavior is investigated. Physics-based simulation models are validated and supplemented through experimental studies. A microstructure-based thermomechanical model of the rubbing process demonstrates that in addition to geometric parameters and mechanical load parameters, microstructural properties such as grain size and grain orientation affect rotor stress and stator deformation. The rotor fin speed, penetration speed, and penetration depth had a major influence on the rubbing characteristics of Haynes 214. Radial and axial rubbing movements in honeycomb liners were evaluated and the resulting contact stresses were compared. In radial penetration, the rubbing characteristics are primarily influenced by the radial contact area. In contrast, during axial penetration, the curvature radius of the rotor fin strongly affects the rubbing properties. Brazed joints in honeycomb seals were integrated into the physical model and experimentally studied. Thermomechanical simulations show that the brazing layer in double-walled honeycomb structures strongly impacts mechanical stress due to its high hardness and potential for brittle failure. The embrittling effect of the brazing layer was experimentally confirmed in tensile tests. Brazing Haynes 214 with the nickel-based brazing alloy BNi-5 reduces strain to rupture from 36% to 18%. Tensile tests at strain rates of up to 50 s-1 showed that both tensile strength and yield strength increased with strain rate. Cracks formed along the brazed joints of rubbed brazed sheets, causing the brazed sheet to split during rubbing. Rubbing seals are often aluminized. Aluminizing prior to the brazing process reduces the wettability of the brazing material, thereby diminishing the capillary effect. As a result, aluminizing before brazing reduces the amount of brazing material that can rise to the rubbing contact area through capillary forces. Aluminizing can negatively impact the rubbing properties, as the resulting nickel aluminide layer increases hardness, and hard chromium carbides form in the diffusion zone. New rhombus sealing systems reduce the contact area and prevent the formation of doublewall regions with brazing layers. Thus, the rhombus sealing system achieved lower mechanical stresses in rubbing tests compared to conventional honeycomb seals.

Publications

• Numerical investigations on the rubbing process in labyrinth seals for full flight mission; Proceedings of the 24th ISABE Conference (2019).
  Munz O., Hühn L., Bleier F., Bauer H.-J.
  
• The Effect of Brazing on Microstructure of Honeycomb Liner Material Hastelloy X. Journal of Materials Engineering and Performance, 28(4), 1909-1913.
  Ulan, kyzy Sonun; Völkl, Rainer; Munz, Oliver; Fischer, Tim & Glatzel, Uwe
  
• Experimental Investigation on the Rubbing Process of Labyrinth Seals Against Honeycomb Liners. Volume 10A: Structures and Dynamics.
  Munz, Oliver; Hühn, Lisa; Schwitzke, Corina; Bauer, Hans-Jörg; Fischer, Tim & Ulan, kyzy Sonun
  
• Thermo-physical properties of Hastelloy X and Haynes 214 close to the melting range. Materials Science and Technology, 36(10), 1012-1019.
  Ulan, kyzy Sonun; Völkl, Rainer; Munz, Oliver; Fischer, Tim; Welzenbach, Sarah & Glatzel, Uwe
  
• Structure-property relationship of a nickel-based honeycomb sealing composite. Computational Materials Science, 190, 110270.
  Fischer, T.; Ulan, kyzy S.; Munz, O. & Werner, E.
  
• Multiscale modeling of the mechanical behavior of brazed Ni-based superalloy sheet metals. Continuum Mechanics and Thermodynamics, 35(1), 211-229.
  Huber, Jakob; Vogler, Jonas & Werner, Ewald
  
• Mechanical and Microstructural Properties of Brazed Honeycomb Liner Material Haynes 214. The Minerals, Metals & Materials Series, 445-452.
  Vogler, Jonas; Song, Jieun; Huber, Jakob; Völkl, Rainer & Glatzel, Uwe
  
• Compositionally Complex Alloy MnFeCoNiCu for Brazing Nickel‐Based Superalloy Haynes 214. Advanced Engineering Materials, 26(14).
  Vogler, Jonas; Schneiderman, Benjamin; Yu, Zhenzhen; Huber, Jakob; Völkl, Rainer & Glatzel, Uwe
  
• High temperature and high strain rate properties of brazed honeycomb liner material Haynes 214. Wear, 550-551, 205427.
  Vogler, Jonas; Völkl, Rainer; Song, Jieun; Viebranz, Vincent Fabian; Huber, Jakob; Bauer, Hans-Jörg; Werner, Ewald & Glatzel, Uwe
  
• Predicting mechanical failure of polycrystalline dual-phase nickel-based alloys by numerical homogenization using a phase field damage model. Continuum Mechanics and Thermodynamics, 36(4), 775-793.
  Huber, Jakob; Vogler, Jonas; Torgersen, Jan & Werner, Ewald