NiAl bond coats made by a directed vapor deposition approach

Intermetallic, nickel aluminide alloys are widely used as bond coat materials in thermal barrier coating systems applied to nickel base super alloy components. They are usually synthesized by a solid-state reaction-diffusion heat treatment following the chemical vapor deposition of aluminum on the nickel rich substrate. Here, an electron beam directed vapor deposition (EB-DVD) technique is used to simultaneously evaporate nickel and aluminum and then reactively deposit NiAl bond coats that are structurally and chemically homogeneous and well bonded to the superalloy substrate. The approach utilizes individual nickel and aluminum sources placed within a rarefied helium gas jet with flow conditions that promote vapor phase intermixing. By adjusting the electron beam current applied to each elemental source, we show that the coating layer composition can be precisely controlled. Fully dense, homogeneous, β-phase NiAl coating layers with a relatively sharp compositional interface with the substrate have been deposited. The extent of the substrate interdiffusion zone is controlled by the deposition conditions.