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Conventionally cast GTD-111EA first stage buckets from GE Frame 5001P-NT engine after 42,000 hours of service, directionally solidified GTD-111DS Frame 5002C buckets after 49,000 hours of service, and conventionally cast IN-738 Frame 5002B buckets after 81,000 hours of service were evaluated before and after refurbishment. These buckets were coated with GT-29, GT-29 plus and RT-22 coatings respectively. Coating condition, microstructural degradation, tensile properties, and creep properties were evaluated in the service aged condition. Microstructure was assessed after the hot isostatic pressing (HIP) and solution heat treatment and again after the full refurbishment and recoating of the buckets. It was found that the GT-29 coating was breached 100% by oxidation in the 5001P engine after service. The GT-29 plus coating on the 5002C engine was breached very slightly and the majority of the coating was still in good condition. The RT-22 coating on the IN-738 bucket was stripped before it was received for evaluation at SwRI. Gamma prime growth, coalescence and agglomeration were found in all of the buckets. Continuous carbide network near the airfoil leading edge was found in the GTD-111EA bucket. Significant improvement in the microstructural condition was observed after the refurbishment for the GTD-111 buckets. However, the gamma prime morphology was not normal for the IN-738 bucket. Both tensile and creep properties of the GTD-111 buckets showed significant improvement after refurbishment. However, for the IN-738 bucket little improvement on the mechanical properties was observed. The reasons for this and the correlation between the microstructure and properties are discussed in this paper.

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Solid particle erosion (SPE) and liquid droplet erosion (LDE) cause severe damage to turbine components and lead to premature failures, business loss, and repair costs to power plant owners and operators. Under a program funded by the Electric Power Research Institute, TurboMet International and Southwest Research Institute (SRI) have developed hard erosion resistant nanocoatings and have conducted evaluation tests. These coatings are targeted for application in steam and gas turbines to mitigate the adverse effects of SPE and LDE on rotating blades and stationary vanes. Based on a thorough study of the available information, the most promising coatings, such as nanostructured titanium silicon carbonitride (TiSiCN), titanium nitride (TiN), and multilayered nanocoatings, were selected. State-of-the-art nanotechnology coating facilities at SwRI were used to develop the coatings. The plasma enhanced magnetron sputtering method was used to apply these coatings on various substrates. Ti–6Al–4V, 12Cr, 17-4PH, and custom 450 stainless steel substrates were selected based on the current alloys used in gas turbine compressors and steam turbine blades and vanes. Coatings with up to 30μm thickness have been deposited on small test coupons. Initial screening tests on coated coupons by solid particle erosion testing indicate that these coatings have excellent erosion resistance by a factor of 20 over the bare substrate. Properties of the coating, such as modulus, hardness, microstructural conditions including the interface, and bond strength, were determined. Tensile and high-cycle fatigue tests on coated and uncoated specimens indicate that the presence of the coatings has no negative effects but has a positive influence on the high-cycle fatigue strength at zero and high mean stresses.

Degradation of microstructure and mechanical properties of a service run GTD-111 DS blade was evaluated. The blade was coated with a CoCrAlY coating (GT-29) and had operated on a GE Model MS 5002 engine for 54,850 hours. To recover the microstructure of the degraded blade, the effect of solution treatment temperature on the microstructure and properties was evaluated. The blanks removed from the airfoil tip section were given a commonly used partial solution treatment 2050°F (1120°C) for GTD-111 and a high temperature solution treatment 2175°F (1190°C) prior to the partial solution and aging treatments. Microstructure and creep test results of these heat treated specimens revealed that the high temperature solution treatment was necessary to recover the microstructure and properties of in-service degraded GTD-111 DS buckets.