Primary surface recuperator alloy oxidation: A comparison of accelerated engine testing to field operation

The Capstone C65 MicroTurbine¹ Primary Surface Recuperator (PSR) core has been manufactured from Haynes alloy HR-120² since 2005. When exposed to the harsh operating environment of the microturbine PSR, HR-120 forms a protective oxide scale that is resistant to the effects of the water vapor present in the exhaust gas. Long-term accelerated microturbine testing, with samples in a modified PSR with a removable aft dome, is on-going at an elevated Turbine Exit Temperature (TET) ∼100°F higher than normal operation. The elevated TET test engine is operated at steady state conditions and the engine is shut down at pre-determined intervals for sample removal. Material characterization of the elevated TET samples has been carried out by Capstone Turbine Corporation in collaboration with Oak Ridge National Laboratory. The surface oxide scale formation and associated alloy compositional changes have been evaluated for elevated TET samples with operating lives ranging from ∼1,800 - ∼26,500 hours. In addition, field operated HR-120 recuperators have been sectioned and samples have been evaluated for operating lives ranging from ∼5,500 - ∼18,000 hours. Results from the microstructural and compositional analyses of both the longterm steady-state elevated TET HR-120 samples, and the field operated HR-120 recuperator samples, will be presented and compared.