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Research Papers

Evolution of Surface Deposits on a High-Pressure Turbine Blade—Part I: Physical Characteristics

[+] Author and Article Information
James E. Wammack, Jared Crosby, Daniel Fletcher, Jeffrey P. Bons

Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602

Thomas H. Fletcher

Department of Chemical Engineering, Brigham Young University, Provo, UT 84602

J. Turbomach 130(2), 021020 (Mar 25, 2008) (8 pages) doi:10.1115/1.2752182 History: Received September 08, 2006; Revised November 14, 2006; Published March 25, 2008

Abstract

Turbine blade coupons with three different surface treatments were exposed to deposition conditions in an accelerated deposition facility. The facility simulates the flow conditions at the inlet to a first stage high-pressure turbine ($T=1150°C$, $M=0.31$). The combustor exit flow is seeded with dust particulate that would typically be ingested by a large utility power plant. The three coupon surface treatments included: (1) bare polished metal; (2) polished thermal barrier coating with bondcoat; and (3) unpolished oxidation resistant bondcoat. Each coupon was subjected to four successive $2h$ deposition tests. The particulate loading was scaled to simulate 0.02 parts per million weight (ppmw) of particulate over $3months$ of continuous gas turbine operation for each $2h$ laboratory simulation (for a cumulative $1year$ of operation). Three-dimensional maps of the deposit-roughened surfaces were created between each test, representing a total of four measurements evenly spaced through the lifecycle of a turbine blade surface. From these measurements the surface topology and roughness statistics were determined. Despite the different surface treatments, all three surfaces exhibited similar nonmonotonic changes in roughness with repeated exposure. In each case, an initial buildup of isolated roughness peaks was followed by a period when valleys between peaks were filled with subsequent deposition. This trend is well documented using the average forward facing roughness angle in combination with the average roughness height as characteristic roughness metrics. Deposition-related mechanisms leading to spallation of the thermal barrier coated coupons are identified and documented.

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Figures

Figure 1

Distribution of Ra(μm) for multiple aero and land-based turbine blades (from Refs. 5-6)

Figure 2

Turbine Accelerated Deposition Facility

Figure 3

Schematic of TADF turbine coupon holder

Figure 4

Streamwise-averaged surface traces of the bare metal coupon deposit at five different points in its evolution

Figure 5

Surface topologies of 3mm×5mm section of deposit on bare metal coupon after each burn. Vertical scale shows peak roughness height: (a) before Burn 1, (b) after Burn 1; (c) after Burn 2; (d) after Burn 3; and (e) after Burn 4.

Figure 6

Roughness statistics for the bare metal coupon deposit

Figure 12

ESEM cross section of spalled region of the TBC1 coupon and spalled chip: (a) edge of spalled TBC chip removed after Burn 3 (image enlarged for clarity—see scale); and (b) spalled region of TBC1 coupon after Burn 4

Figure 11

Roughness statistics for the unpolished coupon deposit

Figure 10

Surface topologies of 8mm×18mm section of deposit on unpolished coupon after each burn. Vertical scale shows peak roughness height: (a) before Burn 1; (b) after Burn 1; (c) after Burn 2; (d) after Burn 3; and (e) After Burn 4.

Figure 9

Roughness statistics for the TBC1 and TBC2 coupon deposits

Figure 8

Surface topologies of 5.7mm×9.5mm section of deposit on the TBC1 coupon after each burn. Vertical scale shows peak roughness height: (a) before Burn 1; (b) after Burn 1; (c) after Burn 2; (d) after Burn 3; and (e) after Burn 4.

Figure 7

Streamwise-averaged surface traces of the TBC1 coupon deposit at five different points in its evolution

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