Fiber-Reinforced Superalloys For Rocket Engines
High pressure turbopumps for advanced reusable liquid propellant rocket engines such as that for the Space Shuttle Main Engine (SSME) require turbine blade materials that operate under extreme conditions of temperature, hydrogen environment, high-cycle fatigue loading, thermal fatigue and thermal shock. Such requirements tax the capabilities of current blade materials. Based on projections of properties for tungsten fiber reinforced superalloy (FRS) composites, it was concluded that FRS turbine blades offer the potential of a several fold increase in life and over a 200 C increase in temperature capability over the current SSME blade material. FRS composites were evaluated with respect to mechanical property requirements for SSME blade applications. Compared to the current blade material, the thermal shock resistance of FRS materials is excellent, two to nine times better, and their thermal fatigue resistance is equal to or higher than the current blade material. FRS materials had excellent low and high-cycle fatigue strengths, and thermal shock-induced surface microcracks had no influence on their fatigue strength. The material also exhibited negligible embrittlement when exposed to a hydrogen environment.
Tungsten fiber reinforced FeCralY: A first generation composite turbine blade material
Tungsten-fiber/FeCrAlY (W/FeCrAlY) was identified as a promising aircraft engine, first generation, turbine blade composite material. Based on available data, W/FeCrAlY should have the stress-rupture, creep, tensile, fatigue, and impact strengths required for turbine blades operating from 1250 to 1370 K. It should also have adequate oxidation, hot corrosion, and thermal cycling damage resistance as well as high thermal conductivity. Concepts for potentially low cost blade fabrication were developed. These concepts were used to design a first stage JT9D convection cooled turbine blade having a calculated 50 K use-temperature advantage over the directionally solidified superalloy blade.
Microstructure and Fatigue Behavior of Nickel-base Eutectic Composites
The high cycle fatigue bahavior of three advanced nickel-base eutectic composites, Nitac 14B, Cotac 744 and AG-170 (γ/γ′-α) has been determined at 25°C and 825°C. Nitac 14B displays superior fatigue resistance at high stress levels at 25°C, and at all stress levels at 825°C. Transmission electron microscopy revealed dislocation motion in TaC fibers of Nitac 14B during fatigue at 25°C and in molybdenum fibers (AG-170) at both 25°C and 825°C. In addition, precipitate particles have been observed within the molybdenum fibers after cyclic loading at 825°C. The relationships among observed microstructural changes, fractographic features and fatigue behavior is discussed.