Development of Ni–Mn-based alloys for the fast epitaxial braze-repair of single-crystalline nickel-based superalloys

Abstract

Abstract Diffusion brazing is a widely-used technology for the repair of cracks in hot section turbine components, mostly fabricated from nickel-based superalloys. However, the filling of wide cracks in the range of 100–300 μm is difficult since the precipitation of brittle secondary phases, which are formed by the conventionally used melting point depressants B and Si, leads to deteriorating mechanical properties. Therefore, new Ni – Mn-based braze alloys were developed which allow a very fast epitaxial healing of particularly wide cracks in single-crystalline components. As B and Si are replaced by Mn, the repair process can be significantly shortened since the epitaxial solidification is not completely controlled by diffusion but can also be controlled by cooling. Ni – Mn-based systems enhanced by Al, Cr and Ti were investigated. In this work an improved brazing cycle for the minimization of porosity within the braze gap as well as an enhanced heat treatment, which produces a γ/γ′ microstructure very similar to the parent material, are presented. Results from tensile tests at room temperature and at 900 °C conducted on 300 μm gap width samples are discussed.