Improved Bond Coats for Thermal Spray Instrumentation

摘要

Several surface treatments and heat treatments were investigated to increase the fatigue life of thermalsprayed instrumentation for use in gas turbine engines. A NiCoCrAlY bond coat (Praxair 171) wasfound to have a substantially longer fatigue life than NiCrAlY bond coats (Praxair 343). Selectiveoxidation of NiCoCrAlY bond coats in reduced oxygen partial pressures to 1750 °F (954 °C) was foundto double the fatigue life of the thermal spray instrumentation. However, heat treatments of the NiCrAlYbond coats in reduced oxygen partial pressures had little or no effect on the fatigue life of the thermalspray instrumentation. Sputtered platinum diffusion barriers were also used in conjunction with thereduced oxygen partial pressure heat treatments and lead to a four fold increase in the fatigue life ofthermal spray instrumentation, whereas electroplated rhodium diffusion barriers yielded only a marginalincrease in fatigue life. In addition to these surface treatments and heat treatments, a series of combinatorial libraries using various mixtures of Al2O3 and NiCoCrAlY were prepared to determine anoptimal intermediate thermal spray coating that would reduce interfacial stresses and provide a bettermatch of thermal expansion coefficients between the metallic bond coat and the ceramic top coat. Themerits of each of the techniques to improve the fatigue life of the various bond coats used for thermalsprayed instrumentation are presented within.