Development of ODS Coating for Critical Turbine Components Using DED Additive Manufacturing

摘要

The challenge for design and manufacturing of future advanced gas turbine systems is to meet the requirement of increasing turbine inlet temperature (TIT), which is higher than the substrate melting temperature. Increasing high thermal load also causes severe oxidation and corrosion of base alloy in gas turbine. Current approach is coating the inlet turbine blade with thermal barrier coating (TBC) combined with internal cooling channel in the substrate. However, neither the ceramic coating layer nor the metallic bond coat in the TBC system can provide structural loading support to house the internal cooling channels. Development of structural bond coat with embedded cooing channels can be one of the key technologies for future advanced turbine systems. In this research, high temperature protective structural coating on top of a superalloy substrate (popular for making gas turbine component) 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 suitable for AM applications. AM-processed ODS coating by direct energy deposition (DED) method on MAR-247 substrate were carried out. The ODS coated samples were then subjected to cyclic thermal loadings for over 4000 cycles (each cycle consists of alternating between 45 minutes at 1100 °C and 45 minutes at room temperature). SEM and EDX were applied for oxide formation analyses of the ODS coating at selected thermal cycles. In particular, stability of gamma prime phase in the ODS coating at different thermal cycles is analyzed. Test results revealed a thin continuous durable alumina oxide layer on ODS coating surface after over 4,000 thermal cycles. Test results also showed relatively stable substrate microstructures due to the protective alumina surface oxide layer and strong bonding at ODS coating/substrate interface is maintained. Oxidation weight gain of a AM-processed ODS sample is conducted and the results compared favorably with those literature available alumina forming alloys (AFA) under similar testing conditions.