Brazed coatings for steam turbine blades: impact of the tape architecture and composition on mechanical properties

Abstract

Abstract Ni-based brazing coatings with tungsten or chromium carbides are used for wear and corrosion protection in various applications. Steam turbine blades especially present a highly stressed application in which in particular the resistance to erosion and corrosion is essential. Therefore, novel tape architectures of brazed coatings have been developed and investigated within this study. In contrast to the use of powders, the application by means of tapes offers a high potential with regard to later use in industry due to the reproducible handling and automation. In this work, different coating systems were successfully deposited by means of vacuum brazing on X12CrNiMo-12 steel substrate. In order to achieve a sufficient fracture toughness of the coatings, pure nickel powder was added to the tapes. The influence of this additive on the mechanical properties was analyzed by means of three-point bending tests. A positive effect has been observed when adding a volume fraction of φ(Ni) = 25% of nickel, increasing the flexural strength up to σf = 580 MPa. Furthermore, the surface hardness of the coating has been analyzed depending on coating architecture and post-deposition treatment by grinding.