John Gayda

Low cycle fatigue behaviour of a plasma-sprayed coating material

Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C, but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

Quench crack behavior of nickel-base disk superalloys

There is a need to increase the temperature capability of superalloy turbine disks to allow higher operating temperatures in advanced aircraft engines. When modifying processing and chemistry of disk alloys to achieve this capability, it is important to preserve the ability to use rapid cooling during supersolvus heat treatments to achieve coarse grain, fineγ′ microstructures. An important step in this effort is an understanding of the key variables controlling the cracking tendencies of nickel-base disk alloys during quenching from supersolvus heat treatments. The objective of this study was to investigate the quench cracking tendencies of several advanced disk superalloys during simulated heat treatments. Miniature disk specimens were rapidly quenched after solution heat treatments. The responses and failure modes were compared and related to the quench cracking tendencies of actual disk forgings. Cracking along grain boundaries was generally observed to be operative. For the alloys examined in this study, the solution temperature, not alloy chemistry, was found to be the primary factor controlling quench cracking. Alloys with high solvus temperatures show greater tendency for quench cracking.

Creep Property Characterization of Potential Brayton Cycle Impeller and Duct Materials

This paper represents a status report documenting the work on creep of superalloys performed under Project Prometheus. Cast superalloys have potential applications in space as impellers within closed-loop Brayton cycle nuclear power generation systems. Likewise wrought superalloys are good candidates for ducts and heat exchangers transporting the inert working gas in a Brayton-based power plant. Two cast superalloys, Mar-M247LC and IN792, and a NASA GRC powder metallurgy superalloy, LSHR, are being screened to compare their respective capabilities for impeller applications. Several wrought superalloys including Hastelloy X, (Haynes International, Inc., Kokomo, IN), Inconel 617, Inconel 740, Nimonic 263, and Incoloy MA956 (Special Metals Corporation, Huntington, WV) are also being screened to compare their capabilities for duct applications. These proposed applications would require sufficient strength and creep resistance for long term service at temperatures up to 1200 K, with service times to 100,000 h or more. Conventional tensile and creep tests were performed at temperatures up to 1200 K on specimens extracted from the materials. Initial microstructure evaluations were also undertaken.

Modeling Machining Distortion of Aircraft‐Engine Disk Forgings

Rotating components of aircraft engines are generally manufactured by forging followed by heat treatment. Due to the residual stresses induced during heat treatment, components often distort when material is removed during machining to the final shape. Using trial‐and‐error approaches, it can be very difficult to develop a sequence of machining operations which will ensure that the final component is produced within the very tight dimensional tolerances required for satisfactory performance in service. The objective of the current work, therefore, was to develop and validate a simulation procedure that can predict distortion during the material removal process. To validate the model, four prototype disks were forged and then heat treated under different conditions. Multiple machining cuts were carried out on the top side of each disk. The distortion at the bottom surface was then measured. The Finite‐Element Method (FEM) embodied in the commercial software, DEFORM™‐HT, was used to model the four heat‐trea...

Fatigue Behavior of [0] 8 SCS-6/Ti-6Al-4V Composite Subjected to High Temperature Turboshaft Design Cycles

Performance and thrust-to-weight goals of advanced gas turbine engines require significant advances in material capabilities. Titanium matrix composites (TMCs) offer significant opportunities in compressor components to achieve performance improvements by reducing weight and increasing speed. Mission cycle fatigue testing of a [0]{sub 8} SCS-6/Ti-6Al-4V composite was performed. The mission cycle simulates the stress-temperature-time profile in a ring-reinforced impeller of a turboshaft engine. The cycle has a fourteen minute period and attains a peak stress and temperature of 1,100 MPa and 427 C respectively. A fatigue life of 9,528 cycles was achieved. While this life was less than the design goal, 15,000 cycles, a moderate increase in fiber content coupled with a small decrease i peak stress or temperature would probably achieve the stated design goal.