William D. Brentnall

Exposure of Ceramics and Ceramic Matrix Composites in Simulated and Actual Combustor Environments

A high-temperature, high-pressure, tube furnace has been used to evaluate the long term stability of different monolithic ceramic and ceramic matrix composite materials in a simulated combustor environment. All of the tests have been run at 150 psia, 1204 degrees C, and 15% steam in incremental 500 h runs. The major advantage of this system is the high sample throughput; >20 samples can be exposed in each tube at the same time under similar exposure conditions. Microstructural evaluations of the samples were conducted after each 500 h exposure to characterize the extent of surface damage, to calculate surface recession rates, and to determine degradation mechanisms for the different materials. The validity of this exposure rig for simulating real combustor environments was established by comparing materials exposed in the test rig and combustor liner materials exposed for similar times in an actual gas turbine combustor under commercial operating conditions.

Effects of alloy composition on the performance of Yttria stabilized zirconia-thermal barrier coatings

Thermal barrier coatings (TBCs) provide an alloy surface temperature reduction when applied to turbine component surfaces. Thermal barrier coatings can be used as a tool for the designer to augment the power and/or enhance the efficiency of gas turbine engines. TBCs have been used successfully in the aerospace industry for many years, with only limited use for industrial gas turbine applications. Industrial gas turbines operate for substantially longer cycles and time between overhauls, and thus endurance becomes a critical factor. There are many factors that affect the life of a TBC including the composition and microstructure of the base alloy and bond coating. Alloys such as Mar-M 247, CMSX-4, and CMSX-10 are materials used for high temperature turbine environments, and usually require protective and/or thermal barrier coatings for increased performance. Elements such as hafnium, rhenium, and yttrium have shown considerable improvements in the strength of these alloys. However, these elements may result in varying effects on the coatability and environmental performance of these alloys. This paper discusses the effects of these elements on the performance of thermal barrier coatings.

Ceramic Stationary Gas Turbine Development

A program has been initiated under the sponsorship of the Department of Energy (DOE), Office of Industrial Technology, to improve the performance of stationary gas turbines in cogeneration through the selective replacement of metallic hot section parts with uncooled ceramic components. It is envisioned that the successful demonstration of ceramic gas turbine technology, and the systematic incorporation of ceramics in existing and future gas turbines will enable more efficient engine operation, resulting in significant fuel savings, increased output power, and reduced emissions. The program which started in September, 1992, takes an engine of the Solar Centaur family of industrial gas turbines, and modifies the design of the hot section to accept ceramic first stage blades and first stage nozzles, and a ceramic combustor liner. The ceramic materials selected for the blade are silicon nitride, for the nozzle silicon nitride and silicon carbide, and for the combustor liner silicon carbide as well as two continuous fiber reinforced ceramic composites, one with a silicon carbide matrix and another with an oxide matrix.This paper outlines the approach, conceptual component design, and materials selection for the program.Copyright

Service Temperature Estimation of Turbine Blades Based on Microstructural Observations

Optical and electron metallographic 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 that had seen service in land-based gas turbine engines

Material Characterization of Candidate Silicon Based Ceramics for Stationary Gas Turbine Applications

The Ceramic Stationary Gas Turbine (CSGT) Program is evaluating the potential of using monolithic and composite ceramics in the hot section of industrial gas turbines. Solar Turbine’s Centaur 50 engine is being used as the test bed for ceramic components. The first stage blade, first stage nozzle and the combustor have been selected to develop designs with retrofit potential, which will result in improved performance and lowered emissions. As part of this DOE sponsored initiative a design and life prediction database under relevant conditions is being generated. This paper covers experiments conducted to date on the evaluation of monolithic silicon based ceramics. Mechanical property characterizations have included dynamic fatigue testing of tensile as well as flexural specimens at the temperatures representative of the blade root, the blade airfoil and the nozzle airfoil. Data from subcomponent testing of blade attachment concepts are also included.Copyright

Ceramic Stationary Gas Turbine Development Program: Third Annual Summary

The Ceramic Stationary Gas Turbine (CSGT) program has been performed under the sponsorship of the United States Department of Energy, Office of Industrial Technologies and Office of Power Technologies. The objective of the program was to improve the performance of stationary gas turbines in cogeneration by retrofitting uncooled ceramic components into the hot section of the engine. The replacement of previously cooled metallic hot section components with the uncooled ceramics enables improved thermal efficiency, increased output power, and reduced gas turbine emissions. This review summarizes the latest progress on Phase III of the program, which involves 1) preparation for the final in-house CSGT engine test of ceramic blades, nozzles and CFCC liners, and 2) field testing of the CFCC combustor liners at two cogeneration end user sites. The field testing of CFCC combustor liners is now being performed under the Advanced Materials Program, sponsored by DOE, Office of Power Technologies.The Solar Centaur 50S engine, which operates at a turbine rotor inlet temperature (TRIT) of 1010°C, was selected for the developmental program. The program goals include an increase in the TRIT to 1121°C, accompanied by increases in thermal efficiency and output power. This is to be accomplished by the incorporation of ceramic first stage blades and nozzles, and a “hot wall” ceramic combustor liner. The performance improvements are attributable to the increase in TRIT and the reduction in cooling air requirements for the ceramic parts. The “hot wall” ceramic liners also enable a reduction in gas turbine emissions of NOx and CO. This 1121°C TRIT engine test of the ceramic hot section is planned for the first quarter of 2001.The component design and material selection have been previously definitized for the ceramic blades, nozzles and combustor liners. Each of these ceramic component designs was successfully evaluated in short-term engine tests in the Centaur 50S engine test cell facility at Solar. Environmental barrier coatings for the ceramic components are also being optimized. To date, seven field installations of the CSGT Centaur 50S engine totaling over 30,000 hours of operation have been initiated under the program at two industrial cogeneration sites. This paper briefly discusses the recent developmental efforts for the upcoming 1121°C TRIT engine test, but focuses on the various field demonstrations of CFCC combustor liners.Copyright

Effects of Alloy Composition on the Performance of Diffusion Aluminide Coatings

Nickel-based superalloys have been used in the gas turbine hot section components for their outstanding mechanical properties at elevated temperatures. Increasing the alloy strength at high temperature is usually achieved at the expense of the alloy’s environmental stability. Oxidation and high heat flux could be limiting factors in the use of these alloys at temperatures above 1800°F. To help overcome these limitations, protective coatings can be applied to the alloy surfaces to provide oxidation and hot corrosion resistance. These coatings are applied to alloys which can be produced in various forms such as equiaxed, directionally solidified or single crystals with varying chemistries. Elemental additions such as hafnium, rhenium, etc. are added to promote the strengthening of these alloys, and could result in varying effects on the coatability and coating performance. This paper discusses the effects of various substrate elements on the processing and stability of diffusion platinum aluminide coatings.© 1998 ASME

Design of a High Efficiency Industrial Turbine Blade Utilizing Third Generation Single Crystal Alloy CMSX®-10

Future advancements in the efficiency and reliability of Industrial Gas Turbines (IGT) will be closely tied to the application of advanced materials, together with increasingly sophisticated turbine hot section designs. An example of this trend is illustrated by the recent design of a first stage blade component for an advanced IGT concept utilizing the third generation single crystal superalloy CMSX-10. It is anticipated that alloy CMSX-10 will permit the use of increased turbine firing temperatures with reduced cooling flows compared to previous recuperated turbine designs, while maintaining acceptable blade durability and life-cycle cost.This paper discusses some of the design/materials analyses and cost studies performed on the blade, which ultimately led to the consideration of alloy CMSX-10 for the IGT application. The solid modeling and finite element blade design methods which allowed the incorporation of state-of-the-art cooling technology and aerodynamics are described. Alloy CMSX-10 characteristics, particularly mechanical properties and microstructural stability considerations, are discussed. Additionally, the results of a recent casting demonstration in an IGT blade configuration are presented. Finally, future tasks supporting the application of the alloy are outlined, such as coatings development efforts and the DOE/ORNL sponsored Land Based Turbine Casting Initiative; activities sponsored through a cooperative agreement with the United States Department of Energy within the Advanced Turbine System (ATS) Program.© 1997 ASME

Characterization and Performance Evaluation of Pack Cementation and Chemical Vapor Deposition Platinum Aluminide Coatings

Metallurgical evaluation of platinum aluminide coatings applied to industrial gas turbine components, for oxidation and high temperature hot corrosion protection, were conducted. Coatings were processed by electroplating a thin layer of platinum followed by aluminizing using either the pack cementation or the chemical vapor deposition (CVD) processes. Laboratory and field data on the performance of these coatings are presented. Results from these tests showed that both aluminizing processes produced coatings that provided adequate environmental protection. However, the CVD coating experienced less coating growth during engine service and was therefore determined to be thermally more stable than the pack cementation coating in this application.Copyright

CERAMIC STATIONARY GAS TURBINE DEVELOPMENT PROGRAM - FIRST ANNUAL SUMMARY-

A program is being performed under the sponsorship of the United States Department of Energy, Office of Industrial Technology, to improve the performance of stationary gas turbines in cogeneration through the selective replacement of hot section components with ceramic parts. It is envisioned that the successful demonstration of ceramic gas turbine technology, and the systematic incorporation of ceramics in existing and future gas turbines will enable more efficient engine operation, resulting in significant fuel savings, increased output power, and reduced emissions.The engine selected for the program, the Centaur 50 (formerly named Centaur ‘H’) will be retrofitted with first stage ceramic blades, first stage ceramic nozzles, and a ceramic combustor liner. The engine hot section is being redesigned to adapt the ceramic parts to the existing metallic support structure.The work in Phase 1 of the program involved concept and preliminary engine and component design, ceramic materials selection, technical and economic evaluation, and concept assessment. A detailed work plan was developed for Phases II and III of the program. The work in Phase II addresses detailed engine and component design, and ceramic specimen and component procurement and testing. Ceramic blades, nozzles, and combustor liners will be tested in subscale rigs and in a gasifier rig which is a modified Centaur 50 engine. The Phase II effort also involves long term testing of ceramics, development of appropriate nondestructive technologies for part evaluation, and component life prediction. Phase III of the program focuses on a 4,000 hour engine test at a cogeneration site.This paper summarizes the progress on the program through the end of 1993.Copyright