ODS Coating for Critical Turbine Components Using DED Additive Manufacturing

Abstract

A method to fabricate high temperature protective structural coating on top of critical gas turbine components by additive manufacturing (AM) technique using oxide dispersion strengthening (ODS) powder is presented. A novel combined mechanochemical bonding (MCB) plus ball milling (BM) process is utilized to produce ODS powders with nano-crystalline gamma prime phase. AM-assisted ODS coating by direct energy deposition (DED) method on MAR-247 substrate, with laser powers from 100W to 200W were carried out. The ODS coated samples were then subjected to cyclic thermal loadings for over 2000 cycles. Depth-profiling x-ray photoelectric spectroscopy (DP-XPS) was applied for detailed oxide formation analyses through the ODS coating layer at various thermal cycles. Corresponding mechanical properties such as Young’s modulus, yield strength and hardening component of ODS coating samples at various thermal cycles were measured at room temperature using an in-house developed non-destructive spherical micro-indentation testing method. Correlation of the measured mechanical properties with evolution of the ODS microstructures are studied. In particular, stability of gamma prime phase in the ODS coating after thermal cycles is analyzed. Test results revealed a thin steady durable alpha alumina oxide layer on ODS coating surface. After 2,200 thermal cycles, strong bonding at ODS/substrate interface is maintained for ODS coated samples with 200W laser power. Test results also showed stable substrate microstructures due to the protective ODS coating even after 2,200 thermal cycles.