PVD TBC experience on GE aircraft engines
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PVD TBC Experience on GE Aircraft Engines A. Maricocchi, A. Bartz, and D. Wortman The higher performance levels of modern gas turbine engines present significant challenges in the reliability of materials in the turbine. The increased engine temperatures required to achieve the higher performance levels reduce the strength of the materials used in the turbine sections of the engine. Various forms of thermal barrier coatings have been used for many years to increase the reliability of gas turbine engine components. Recent experience with the physical vapor deposition process using ceramic material has demonstrated success in extending the service life of turbine blades and nozzles. Engine test results of turbine components with a 125 lain (0.005 in.) PVD TBC have demonstrated component operating temperatures of 56 to 83 *C (100 to 150 ~ lower than non-PVD TBC components. Engine testing has also revealed that TBCs are susceptible to high angle particle impact damage. Sand particles and other engine debris impact the TBC surface at the leading edge of airfoils and fracture the PVD columns. As the impacting continues, the TBC erodes in local areas. Analysis of the eroded areas has shown a slight increase in temperature over a fully coated area; however, a significant temperature reduction was realized over an airfoil without TBC.
IKeywords microstructure,performance.PVD coatings.TBCs
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1. Introduction THE DRIVEFOR increased aircraft engine thrust and fuel efficiency has resulted in continual increases in hot section temperatures. Several generations of superalloys have been developed over the past 20 years to make these increases in turbine inlet temperature possible. However, the limits of stress rupture, surface protection, and melting point make this increasingly difficult. In addition, the amount of air that can be used for cooling in high-performance engines is limited. The use of thermal barrier coating (TBC) has the potential to extend these advances in aircraft engine development by providing a layer of thermal insulation between the superalloy turbine airfoil and the hot gases (Fig. 1). With the turbine airfoil cooling technology available today, a 250 p.m (0.010 in.) thick TBC can reduce the average metal temperature by 111 to 167 ~ (200 to 300 ~ (Ref 1). Designing a TBC for full thermal insulating benefit requires high confidence because loss of the TBC could result in rapid component degradation. The payoff in increased engine thrust of fuel efficiency is significant; therefore, much effort is being focused on improvements in the reliability of TBCs. Additional effort is being expended to further the understanding of the behavior of TBCs. Thermal barrier coatings have been used extensively since the mid 1970s for life extension of combustor and afterburner components. Plasma-sprayed zirconia, with 7% yttria (YSZ) for stabilization of the tetragonal phase, was determined to be most successful for these applications. Very low thermal conductivity, high melting point, inertness, and relatively high coeffici
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