Research Papers: Gas Turbines: Ceramics

Vapor Phase Deposition Using a Plasma Spray Process

[+] Author and Article Information
Konstantin von Niessen, Malko Gindrat

 Sulzer Metco AG, Rigackerstrasse16, CH-5610 Wohlen, Switzerland

J. Eng. Gas Turbines Power 133(6), 061301 (Feb 14, 2011) (7 pages) doi:10.1115/1.4002469 History: Received May 12, 2010; Revised August 12, 2010; Published February 14, 2011; Online February 14, 2011

Plasma spray-physical vapor deposition (PS-PVD) is a low pressure plasma spray technology recently developed by Sulzer Metco AG (Switzerland) to deposit coatings out of the vapor phase. PS-PVD is developed on the basis of the well established low pressure plasma spraying technology. In comparison to conventional vacuum plasma spraying and low pressure plasma spraying, these new processes use a high energy plasma gun operated at a work pressure below 2 mbar. This leads to unconventional plasma jet characteristics, which can be used to obtain specific and unique coatings. An important new feature of PS-PVD is the possibility to deposit a coating not only by melting the feed stock material, which builds up a layer from liquid splats, but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional PVD technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and electron beam-physical vapor deposition (EB-PVD) coatings. In contrast to EB-PVD, PS-PVD incorporates the vaporized coating material into a supersonic plasma plume. Due to the forced gas stream of the plasma jet, complex shaped parts like multi-airfoil turbine vanes can be coated with columnar thermal barrier coatings using PS-PVD. Even shadowed areas and areas, which are not in the line-of-sight to the coating source, can be coated homogeneously. This paper reports on the progress made by Sulzer Metco to develop a thermal spray process to produce coatings out of the vapor phase. Columnar thermal barrier coatings made of yttria stabilized zircona are optimized to serve in a turbine engine. This includes coating properties like strain tolerance and erosion resistance but also the coverage of multiple air foils.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Images of the plasma jets expanding at different pressures (a) 950 mbar (APS), (b) 50 mbar (VPS/LPPS), and (c) 1 mbar (PS-PVD)

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Figure 2

PS-PVD system with a vertical process chamber and horizontal part manipulator including a transfer chamber

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Figure 3

TBC coating of 7YSZ using different PS-PVD plasma parameters showing (a) splat-like structure and (b) columnar structure

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Figure 4

Optical spectrum of the plasma jet (Ar/He) with 7YSZ corresponding to coatings having (a) no columnar structure and (b) with columnar structure

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Figure 5

Typical EB-PVD 7YSZ TBC microstructure in cross section, the lower picture is a higher magnification of the top picture (courtesy of U. Schulz, DLR, Institute of Materials Research, Cologne, Germany)

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Figure 6

Columnar TBC top layer deposited with PS-PVD1 on a MCrAlY bond coat (the lower picture is a higher magnification of the top picture)

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Figure 7

Relative erosion resistances of different coatings produced by PS-PVD (PS-PVD1, not optimized and PS-PVD2, optimized), APS, and EB-PVD as reference

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Figure 8

Optimized PS-PVD columnar TBC structure deposited on a MCrAlY bond coat

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Figure 9

Relative FCT results of samples with different bond coats and PS-PVD topcoats and the EB-PVD as reference

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Figure 10

Drawing of a simplified double vane dummy with parallel platforms and solid airfoils

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Figure 11

Double vane dummy with a YSZ TBC coating deposited with PS-PVD

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Figure 12

Cut up plan for the vane dummy and the location of the thickness measurements and cross section

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Figure 13

Coating thickness distribution of a PS-PVD coated dummy double vane after 30 min of coating operation

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Figure 14

Columnar microstructure at shadowed areas of the double vane dummy: (a) measuring point 8 leading airfoil, (b) measuring point D platform, and (c) measuring point 4 trailing airfoil



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