Improved Bond Coats for Thermal Spray Instrumentation

摘要

Several surface treatments and heat treatments were investigated to increase the fatigue life of thermal sprayed instrumentation for use in gas turbine engines. A NiCoCrAlY bond coat (Praxair 171) was found to have a substantially longer fatigue life than NiCrAlY bond coats (Praxair 343). Selective oxidation of NiCoCrAlY bond coats in reduced oxygen partial pressures to 1750 °F (954°C) was found to double the fatigue life of the thermal spray instrumentation. However, heat treatments of the NiCrAlY bond coats in reduced oxygen partial pressures had little or no effect on the fatigue life of the thermal spray instrumentation. Sputtered platinum diffusion barriers were also used in conjunction with the reduced oxygen partial pressure heat treatments and lead to a four fold increase in the fatigue life of thermal spray instrumentation, whereas electroplated rhodium diffusion barriers yielded only a marginal increase in fatigue life. In addition to these surface treatments and heat treatments, a series of combinatorial libraries using various mixtures of Al_(2)O_(3) and NiCoCrAlY were prepared to determine an optimal intermediate thermal spray coating that would reduce interfacial stresses and provide a better match of thermal expansion coefficients between the metallic bond coat and the ceramic top coat. The merits of each of the techniques to improve the fatigue life of the various bond coats used for thermal sprayed instrumentation are presented within.