AVS 53rd International Symposium
    Advanced Surface Engineering Friday Sessions
       Session SE1-FrM

Paper SE1-FrM3
Effect of a BN Interlayer on the Tensile Strength of NiAl Coated Sapphire Fibers

Friday, November 17, 2006, 8:40 am, Room 2007

Session: Coatings with Enhanced Thermal Stability & MAX Phases
Presenter: D.E. Hajas, RWTH-Aachen University, Germany
Authors: D.E. Hajas, RWTH-Aachen University, Germany
S. Kyrsta, CemeCon AG, Germany
J.M. Schneider, RWTH-Aachen University, Germany
Correspondent: Click to Email
Intermetallic Matrix Composites (IMCs) can be fabricated by diffusion bonding of coated fiber bundles. Continuous single crystal @alpha@-Al@sub 2@O@sub 3@ fibers were coated with NiAl, h-BN and h-BN-NiAl using Chemical Vapor Deposition (CVD) for the h-BN interlayer and Physical Vapor Deposition (PVD) for the NiAl matrix material. The strength of the coated fibers was evaluated by tensile testing and compared to the strength of uncoated fibers. The effect of temperature during diffusion bonding on the fiber strength was studied. The influence of the coating on the fiber strength was evaluated by etching experiments. Fibers without h-BN interlayer cracked during heat treatment and testing could not be performed. This may be due to thermal stress induced fiber fracture during cooling. However, fibers coated with h-BN interlayer retained approximately 60% of their initial strength after the heat treatment. Two types of morphological features were identified which in combination with thermal stresses may be responsible for the strength degradation of annealed h-BN-NiAl coated fibers: Surface diffusion of the @alpha@-Al@sub 2@O@sub 3@ into cracks in the h-BN interlayer and reaction of the @alpha@-Al@sub 2@O@sub 3@ with impurities on the fiber surface.