Correlative 3D Characterization of High Temperature Oxide Scales on Co-Base Superalloys Using Nano-CT and FIB/SEM Tomography

Abstract

In this contribution, we report on two Co-base superalloys oxidized under synthetic air (20% O2) at 900°C for 12-100 h. A simple ternary superalloy (Co-9Al-9W) and a multinary superalloy (ERBOCo-1) are compared [1]. The superior oxidation properties of the multinary alloy have been shown in previous studies by thermogravimetry and the respective mass gain during isothermal oxidation [2]. To understand this improvement, we combined electron microscopy and X-ray nano-tomography (NanoCT) to reveal the three-dimensional (3D) structure and chemistry of the oxide scales including their layered structure, depth-dependent porosity, and formation of foreign phases. Cross-section images suggest that the ternary alloy Co-9Al-9W exhibits a highly porous transition layer and topologically closed packed (TCP) phase formation while the oxide scales of ERBOCo-1 consist of two porous layers, containing spinels and oxides, and a discontinuous alumina barrier layer.