Deformation behavior of ReCr sigma phase diffusion barrier on Ni-based superalloy

In order to attain a better oxidation resistance of Ni-based superalloys for high performance engines, a ReCr-based σ-phase diffusion barrier coating between the MCrAlY bond coat (Al reservoir) layer and a Ni-based superalloy substrate has been proposed to suppress the diffusion of Al and other elements. The deformation behavior of TMS82+ superalloy specimens with coating layers composed of an Al-rich surface layer (corresponding to a bond coat) and a ReCr σ-phase inner layer is investigated. In-situ observation of the bending tests using a Laser scanning confocal microscopy revealed that the crack formation in the Al-rich surface layer(s) on the tension side of the bend specimen occurs at an early stage of bending. On the other hand, small cracks in the σ-phase layer under the Al-rich surface layer(s) are formed at the slip traces in the Ni-based superalloy single crystal substrate. This suggests a good adhesion between the σphase and the Ni-based superalloy. At the compression side, in both the Al-rich surface layer(s) and the σ-phase layer no cracking was observed until the Al-rich surface layer(s) shows buckling.