Massimo Giannozzi

The Dynamic Influence of Crystal Orientation on a Second Generation Single Crystal Material for Turbine Buckets

High cycle fatigue is a factor that influence gas turbine buckets lifetime and it’s due to high frequency vibrations during service. Rotation and fluid flow around the blades cause static and dynamic stresses on the buckets row. For this reason the natural frequencies and HCF resistance evaluation are fundamental in the design phase of gas turbine engines in order to avoid resonance problems during service. Single crystal and directionally solidified superalloys shows anisotropic material properties, in particular single crystal can be modeled as orthotropic material in lattice directions for FEM simulations purposes. In this paper the influence of the lattice growth orientation, identified by two angles, on the natural frequencies of first stage bucket has been investigated. Six-sigma analysis has been performed in order to obtain a transfer function between lattice orientation and bucket vibration. The Design of Experiment (DoE) has been performed using FEA modal results on ten different vibration modes. The results obtained by FEA are verified by an experimental test on the real Heavy Duty MS5002 buckets.Copyright

New high-temperature seal system for increased efficiency of gas turbines

With increasing fuel prices and significant pressure to reduce emissions, the efficient use of fuels in gas turbines is gaining ever more attention. Abradable seals in gas turbine compressors have contributed to improved efficiencies for quite some time now. To further enhance efficiency, current efforts focus on the seals in one of the hottest sections of the engine, the first turbine stage. Sulzer Metco and GE have designed and tested a new high-pressure turbine abradable seal system in the framework of a European consortium project led by GE Oil & Gas. In the scope of this project, Sulzer Metco developed a novel ceramic coating for application by atmospheric plasma spraying (APS). An engine test verified performance and economic advantages of the new seal system. The measured improvements in engine performance exceed the expected gains as predicted by model calculations.

Clearance Reduction and Performance Gain Using Abradable Material in Gas Turbines

An improvement in the energy efficiency of industrial gas turbines can be accomplished by developing abradable seals to reduce the stator/rotor gap to decrease the tip leakage flow of gases in the hot gas components of the turbine. “ABRANEW” is a project funded by the European Commission aimed at developing a high temperature abradable material capable of controlled abrasion and resistant to erosion and oxidation. In order to define the basic parameters such as the component shape, the existing gap, the expected gap reduction, the seal thickness and other geometric parameters, a comprehensive review of the design of the blade/shroud/casing system was performed.Copyright

Novel Ceramic Abradable Coatings With Enhanced Performance

Abradable coatings are employed in modern gas turbine engines to minimize clearance and reduce over-tip leakage by allowing blade tips to cut into the coating. While such clearance control coatings have been used in the compressor modules of jet engines and stationary gas turbines for many years, their use in the High Pressure (HP) section of turbine modules is relatively new. Because of the high temperatures encountered there, ceramic materials must be used to provide a durable seal. In this paper the performance of two novel ceramic abradable seal coatings is reviewed and compared to a baseline system. Emphasis is placed on the resistance to thermal shock and erosion. The abradability of coatings by hard tipped blades is reviewed using a wear map consisting of five distinctly different rub test conditions. Among the coatings considered, an APS sprayed dysprosia stabilized zirconia ceramic abradable offers a potentially superior combination of thermal shock resistance, abradability and erosion resistance for high temperature turbine seal applications.© 2006 ASME

Damage Evolution and Failure Mechanisms for APS-TBCS

Thermal barrier coatings (TBC-s) have been utilized in gas turbine engines for over two decades, primarily to protect the existing materials under the demands for higher temperatures and greater engine efficiency. Atmospheric Plasma Sprayed TBC, commonly used for hot combustion chamber components of advanced gas turbines, are exposed to thermo-mechanical loads, which may lead to failure in form of macroscopic spallations from the metallic component. The durability of TBC is limited by the interaction of different processes and parameters, such as bond coat oxidation, cyclic strains, visco-plastic and relaxation properties, interface roughness and others. In this work, the spallation failure mechanisms and damage evolution of APS-TBC system are investigated on samples aged by isothermal and thermal cycle tests using different time and temperatures exposures. Several parameters have been analyzed by SEM and a life prediction model approach for APS-TBC is being developed focusing on oxidation kinetics, identifying the parameters such as rumpling, bond coat oxidation, TGO thickness and interdiffusion of base metal elements which drive the oxide formation and TBC spallation mechanisms.Copyright

Increased liquid droplet erosion resistance of steam turbine blades

Abstract Alloys used for the blades of steam turbines usually do not show a satisfactory resistance to erosion and require surface protection with suitable coatings. Starting from the results obtained with Stellite 6 coatings on AISI 420 stainless steel blades, this research has been developed with the aim to increase erosion resistance by modifying the chemical composition of the coatings. Several samples have been coated by laser cladding and exposed to liquid erosion tests. In particular, concentrations of carbide forming and solid solution strengthening elements have been varied in order to establish their effects against liquid droplet erosion. Results of the tests and EDX analyses on the samples are reported, with a discussion on the various effects on erosion resistance. Two directions have appeared as the most promising, either increasing the concentration of carbide forming elements, or increasing the concentration of nickel in the coatings.

Metal Temperature Map Determination of a Serviced Gas Turbine Bucket and Comparison With FEM Temperature Distribution

Nickel-based superalloys are widely used in manufacturing of several important components of aeronautics and land based gas turbines. The good high temperature resistance of these materials is due to their particular microstructure consisting of a FCC lattice nickel matrix, called γ, strengthened by precipitation of a coherent second phase Ni3 (Ti,Al) known as γ′. During service at very high temperatures, γ′ precipitates tend to lose their initial configuration and change their size, shape and distribution, so decreasing material properties, in particular creep resistance. In this work the evolution of microstructure in a serviced first stage bucket from a GE machine has been examined. Several cross sections taken at different heights along the airfoil have been observed by SEM, obtaining a detailed map of the microstructure in the component. A quantitative evaluation of service temperature in the different areas has then been achieved by γ′ precipitates size determination by means of image analysis, combined with a γ′ coarsening model optimized for the particular alloy in use. Temperature values so obtained have been compared with those resulting from the finite element method (FEM) temperature distribution performed during design stage.Copyright