J.M. Aurrecoechea

Elevated-Temperature Creep-Fatigue Crack-Growth Behavior of HAYNES®188 Superalloy

The creep-fatigue crack-growth behavior of HAYNES® 188, a cobalt-based superalloy, was studied at the temperatures of 649, 816, and 927 oC under isothermal conditions. Various hold times at the maximum load were introduced to study the effects of hold time and temperature on the crack-growth behavior. The experiments were conducted under constant stress-intensity-factorrange control modes. Crack lengths were measured by a direct current potential method. The introduction of hold times led to an increase in the cyclic crack-growth rate. As the temperature increases, the time-dependent crack-growth behavior was dominant.

Rainbow Field Test of Coatings for Hot Corrosion Protection of Gas Turbine Blades and Vanes: I — Blade Coatings

A rainbow field test sponsored by the Electric Power Research Institute (EPRI) under contract RP2465-1 was performed to evaluate the comparative hot corrosion resistance of commercially available coatings for gas turbine blades and vanes. The 10,307-hr field test was carried out on a Solar Turbines Incorporated Centaur T-4000 gas turbine operating on a lower grade liquid fuel at the Favianca site of the Owens-Illinois, Inc. glass manufacturing facility in Valera, Venezuela. This paper reviews the results of an evaluation of the performance of three modified aluminides, three MCrAlY overlays, and one duplex NiCoCrAlY/ZrO2-2OY2O3 overlay applied as coatings to the first-stage MAR-M421 and IN-738LC rotor blades, Visual and metallographic examination and remnant coating thickness measurements established that the MCrAlY overlay coatings were generally more effective than a Cr-aluminide and two Pt-aluminides protecting the first-stage blades. Individual differences between the various coatings were established. A remnant coating thickness index (RCTI) was defined to express coating survival and protectiveness quantitatively. The results of blade airfoil temperature estimates were correlated with the hot corrosion morphology.© 1989 ASME

Service Temperature Estimation of Turbine Blades Based on Microstructural Observations

Optical and electron metallographic (SEM) examination was performed on MAR-M-421 samples subjected to controlled furnace exposures, to quantify the microstructural changes associated with the prolonged high temperature exposures. Gamma prime size measurements were used to generate a mathematical model, based on diffusion controlled kinetics, designed to estimate temperatures. This computational technique was utilized to estimate exposure temperatures of turbine blades which had seen service in land based gas turbine engines. The engines had accumulated from 1,200 to more than 98,000 hours, operating under a variety of conditions. The procedure is generally applicable to commonly used gamma prime strengthened nickel-base superalloys.Copyright

Cast Iron-Nickel Alloy for Industrial Gas Turbine Engine Applications

Austenitic ductile iron castings have traditionally been used for gas turbine exhaust components that require castability, good machinability, low thermal expansion, and high strength at elevated temperatures. The achievement of optimum properties in austenitic ductile irons hinges on the ability of the foundry to produce nodular graphite in the microstructure throughout the component. In large, complex components, consistently producing nodular graphite is challenging. A high-nickel steel alloy that is suitable for sand castings has been recently developed for industrial gas turbine engine applications. The alloy exhibits similar mechanical and physical properties to austenitic ductile irons, but with improved processability and ductility. This alloy is weldable and exhibits no secondary graphite phase. This paper presents the results of a characterization program conducted on a 35% nickel, high-alloy steel. The results are compared with an austenitic ductile iron of similar composition. Tensile and creep properties from ambient temperature to 760°C (1400°F) are included, along with fabrication experience gained during the manufacture of several sand cast components at Solar Turbines Incorporated. The alloy has been successfully adopted for gas turbine exhaust system components and other applications where austenitic ductile irons have traditionally been utilized. The low carbon content of austenitic steels permits improved weldabilty and processing characteristics over austenitic ductile irons. The enhancements provided by the alloy indicate that additional applications, as both austenitic ductile iron replacements and new components, will arise in the future.Copyright