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Design of Suspension Plasma Sprayed Thermal Barrier Coatings
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0003-1897-0171
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thermal barrier coatings (TBCs) are widely used on gas turbine components to provide thermal insulation, which in combination with advanced cooling, can enable the gas turbine to operate at significantly higher temperatures even above the melting temperature of the metallic components. There is a permanent need,mainly due to environmental reasons, to increase the combustion temperature inturbines, hence new TBC solutions are needed. By using a liquid feedstock in thermal spraying, new types of TBCs can be produced. Suspension plasma/flame or solution precursor plasma spraying are examples of techniques that can be utilized for liquid feedstock thermal spraying. This approach of using suspension and solution feedstock, which is an alternative to the conventional solid powder feedstock spraying, is gaining increasing research interest since it has been shown to be capable of producing coatings withsuperior performance. The objective of this research work was to identify relationships between process parameters, coating microstructure, thermal conductivity and lifetime in suspension plasma sprayed TBCs. A further objective was to utilize these relationships to enable tailoring of the TBC microstructure for superior performance compared to state-of-the-art TBC used in industry today, i.e. solid feedstock plasma sprayed TBCs. Different spraying techniques, namely suspension high velocity oxy fuel, solution precursor plasma and suspension plasma spraying (with axial and radial feeding) were explored and compared to solid feedstock plasma spraying. A variety of microstructures, such as highly porous, vertically cracked and columnar, were produced and investigated. It was shown that there are strong relationships between microstructure, thermo-mechanical properties and performance of the coatings. Specifically, axial suspension plasma spraying wasshown as a very promising technique to produce various microstructures as wellas highly durable coatings. Based on the experimental results, a tailored columnar microstructure design for a superior TBC performance is also proposed.

Place, publisher, year, edition, pages
Trollhättan: University West , 2018. , p. 96
Series
PhD Thesis: University West ; 20
Keywords [en]
Microstructure; Thermal Barrier Coatings; Axial Injection; Suspension Plasma Spraying; Porosity; Thermal Conductivity; Fracture Toughness; Lifetime
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-12336ISBN: 978-91-87531-92-7 (print)ISBN: 978-91-87531-91-0 (electronic)OAI: oai:DiVA.org:hv-12336DiVA, id: diva2:1209589
Public defence
2018-06-15, F104, University West, Trollhättan, 10:15 (English)
Opponent
Supervisors
Available from: 2018-05-25 Created: 2018-05-23 Last updated: 2018-05-25
List of papers
1. Characterization of Thermal Barrier Coatings Produced by Various Thermal Spray Techniques Using Solid Powder, Suspension, and Solution Precursor Feedstock Material
Open this publication in new window or tab >>Characterization of Thermal Barrier Coatings Produced by Various Thermal Spray Techniques Using Solid Powder, Suspension, and Solution Precursor Feedstock Material
2016 (English)In: International Journal of Applied CeramicTechnology, ISSN 1744-7402, Vol. 13, no 2, p. 324-332Article in journal (Refereed) Published
Abstract [en]

Use of a liquid feedstock in thermal spraying (an alternative to the conventional solid powder feedstock) is receiving an increasing level of interest due to its capability to produce the advanced submicrometer/nanostructured coatings. Suspension plasma spraying (SPS) and solution precursor plasma spraying (SPPS) are those advanced thermal spraying techniques which help to feed this liquid feedstock. These techniques have shown to produce better performance thermal barrier coatings (TBCs) than conventional thermal spraying. In this work, a comparative study was performed between SPS- and SPPS-sprayed TBCs which then were also compared with the conventional atmospheric plasma-sprayed (APS) TBCs. Experimental characterization included SEM, porosity analysis using weight difference by water infiltration, thermal conductivity measurements using laser flash analysis, and lifetime assessment using thermo-cyclic fatigue test. It was concluded that SPS coatings can produce a microstructure with columnar type features (intermediary between the columnar and vertically cracked microstructure), whereas SPPS can produce vertically cracked microstructure. It was also shown that SPS coatings with particle size in suspension (D50) <3 μm were highly porous with lower thermal conductivity than SPPS and APS coatings. Furthermore, SPS coatings have also shown a relatively better thermal cyclic fatigue lifetime than SPPS.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2016
Keywords
Thermal spraying, coating, spray techniques
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-8636 (URN)10.1111/ijac.12472 (DOI)000372037300017 ()2-s2.0-84960358653 (Scopus ID)
Note

Article first published online:11 September 2015

Available from: 2015-11-11 Created: 2015-11-11 Last updated: 2018-05-23Bibliographically approved
2. Comparative study of suspension plasma sprayed and suspension high velocity oxy-fuel sprayed YSZ thermal barrier coatings
Open this publication in new window or tab >>Comparative study of suspension plasma sprayed and suspension high velocity oxy-fuel sprayed YSZ thermal barrier coatings
Show others...
2015 (English)In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 268, p. 70-76Article in journal (Refereed) Published
Abstract [en]

Suspension Thermal Spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings. This technique enables the production of much different performance thermal barrier coatings than conventional thermal spraying which uses solid powder as a feedstock material. In this work a comparative study is performed on four different types of thermal barrier coatings sprayed with two different thermal spay processes, suspension high velocity oxy-fuel spraying (SHVOF) and suspension plasma spraying (SPS) using two different water-based suspensions. Tests carried out include microstructural analysis with SEM, porosity analysis using weight difference by water infiltration, thermal conductivity measurements using laser flash analysis and lifetime assessment using thermo-cyclic fatigue tests. The results showed that SPS coatings were much porous and hence showed lower thermal conductivity than SHVOF coatings produced with the same suspension. From the thermo-cycling tests it was observed that the SPS coatings showed a higher lifetime than the SHVOF ones.

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Suspension plasma spraying, Thermal barrier coatings, Suspension high velocity oxy-fuel spraying, Vertical cracks, Thermal conductivity
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-7264 (URN)10.1016/j.surfcoat.2014.11.054 (DOI)000353735300012 ()2-s2.0-84926216396 (Scopus ID)
Conference
6th Rencontres Internationales de la Projection Thermique
Available from: 2015-01-12 Created: 2015-01-09 Last updated: 2018-05-23Bibliographically approved
3. Characterization of Microstructure and Thermal Properties of YSZ Coatings Obtained by Axial Suspension Plasma Spraying (ASPS)
Open this publication in new window or tab >>Characterization of Microstructure and Thermal Properties of YSZ Coatings Obtained by Axial Suspension Plasma Spraying (ASPS)
Show others...
2015 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 24, no 7, p. 1195-1204Article in journal (Refereed) Published
Abstract [en]

The paper aims at demonstrating various microstructures which can be obtained using the suspension spraying technique and their respective significance in enhancing the thermal insulation property of a thermal barrier coating. Three different types of coating microstructures are discussed which were produced by the Axial Suspension Plasma Spraying. Detailed characterization of coatings was then performed. Optical and scanning electron microscopy were utilized for microstructure evaluations; x-ray diffraction for phase analysis; water impregnation, image analysis, and mercury intrusion porosimetry for porosity analysis, and laser flash analysis for thermal diffusivity measurements were used. The results showed that Axial Suspension Plasma Spraying can generate vertically cracked, porous, and feathery columnar-type microstructures. Pore size distribution was found in micron, submicron, and nanometer range. Higher overall porosity, the lower density of vertical cracks or inter-column spacing, and higher inter-pass porosity favored thermal insulation property of the coating. Significant increase in thermal diffusivity and conductivity was found at higher temperature, which is believed to be due to the pore rearrangement (sintering and pore coarsening). Thermal conductivity values for these coatings were also compared with electron beam physical vapor deposition (EBPVD) thermal barrier coatings from the literature and found to be much lower. © 2015 ASM International

Keywords
Coatings; Cracks; Diffusion; Diffusion barriers; Microstructure; Physical vapor deposition; Plasma jets; Plasma spraying; Pore size; Porosity; Scanning electron microscopy; Sintering; Thermal conductivity; Thermal diffusivity; Thermal insulation; Thermal spraying; X ray diffraction; Yttria stabilized zirconia, Axial injections; Columnar microstructures; Nanometer pores; Suspension plasma spraying; Vertical crack, Thermal barrier coatings
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-7886 (URN)10.1007/s11666-015-0263-x (DOI)000363038600008 ()2-s2.0-8494427946 (Scopus ID)
Available from: 2015-08-13 Created: 2015-08-12 Last updated: 2018-05-23Bibliographically approved
4. Influence of Microstructure on Thermal Properties of Axial Suspension Plasma-Sprayed YSZ Thermal Barrier Coatings
Open this publication in new window or tab >>Influence of Microstructure on Thermal Properties of Axial Suspension Plasma-Sprayed YSZ Thermal Barrier Coatings
Show others...
2016 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 25, no 1-2, p. 202-212Article in journal (Refereed) Published
Abstract [en]

Suspension plasma spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings (TBCs) and enables production of coatings with a variety of structures—highly dense, highly porous, segmented, or columnar. This work investigates suspension plasma-sprayed TBCs produced using axial injection with different process parameters. The influence of coating microstructure on thermal properties was of specific interest. Tests carried out included microstructural analysis, phase analysis, determination of porosity, and pore size distribution, as well as thermal diffusivity/conductivity measurements. Results showed that axial suspension plasma spraying process makes it possible to produce various columnar-type coatings under different processing conditions. Significant influence of microstructural features on thermal properties of the coatings was noted. In particular, the process parameter-dependent microstructural attributes, such as porosity, column density, and crystallite size, were shown to govern the thermal diffusivity and thermal conductivity of the coating.

Keywords
axial injection, columnar microstructure, porosity, suspension plasma spraying, thermal conductivity, thermal diffusivity
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-8737 (URN)10.1007/s11666-015-0355-7 (DOI)000374268000021 ()2-s2.0-84953637268 (Scopus ID)
Available from: 2015-12-01 Created: 2015-12-01 Last updated: 2018-05-23Bibliographically approved
5. Influence of Isothermal Heat Treatment on Porosity and Crystallite Size in Axial Suspension Plasma Sprayed Thermal Barrier Coatings for Gas Turbine Applications
Open this publication in new window or tab >>Influence of Isothermal Heat Treatment on Porosity and Crystallite Size in Axial Suspension Plasma Sprayed Thermal Barrier Coatings for Gas Turbine Applications
2017 (English)In: Coatings, ISSN 2079-6412, Vol. 7, no 1, article id 4Article in journal (Refereed) Published
Abstract [en]

xial suspension plasma spraying (ASPS) is an advanced thermal spraying technique, which enables the creation of specific microstructures in thermal barrier coatings (TBCs) used for gas turbine applications. However, the widely varying dimensional scale of pores, ranging from a few nanometers to a few tenths of micrometers, makes it difficult to experimentally measure and analyze porosity in SPS coatings and correlate it with thermal conductivity or other functional characteristics of the TBCs. In this work, an image analysis technique carried out at two distinct magnifications, i.e., low (500×) and high (10,000×), was adopted to analyze the wide range of porosity. Isothermal heat treatment of five different coatings was performed at 1150 °C for 200 h under a controlled atmosphere. Significant microstructural changes, such as inter-columnar spacing widening or coalescence of pores (pore coarsening), closure or densification of pores (sintering) and crystallite size growth, were noticed in all the coatings. The noted changes in thermal conductivity of the coatings following isothermal heat treatment are attributable to sintering, crystallite size growth and pore coarsening

Keywords
axial suspension plasma spraying; thermal barrier coatings; sintering; pore coarsening; nano-sized pores; crystallite size growth; thermal conductivity
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-10505 (URN)10.3390/coatings7010004 (DOI)000395504700004 ()
Available from: 2017-01-09 Created: 2017-01-09 Last updated: 2018-05-23Bibliographically approved
6. Failure analysis of thermally cycled columnar thermal barrier coatings produced by high-velocity-air fuel and axial-suspension-plasma spraying: A design perspective
Open this publication in new window or tab >>Failure analysis of thermally cycled columnar thermal barrier coatings produced by high-velocity-air fuel and axial-suspension-plasma spraying: A design perspective
Show others...
2018 (English)In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 44, no 3, p. 3161-3172Article in journal (Refereed) Published
Abstract [en]

Axial-suspension-plasma spraying (ASPS) is a fairly recent thermal spray technology which enables production of ceramic top coats in TBCs, incorporating simultaneously the properties of both the conventional-plasma sprayed (highly insulating porous structures) and electron-beam-physical-vapor-deposited (strain-tolerant columnar structures) top coats. TBCs are required to insulate the hot components in a gas turbine engine against high temperature and harsh operating conditions. Periodic heating and cooling of turbine engines during operation can create severe thermal cyclic fatigue conditions which can degrade the performance of these coatings eventually leading to the failure. An in-depth experimental investigation was performed to understand the failure behavior of columnar TBCs subjected to thermal cyclic fatigue (TCF) test at 1100 C. The study revealed that the TCF performance was influenced to an extent, by the top coat microstructure, but was primarily affected by the severity of thermally grown oxide (TGO) growth at the bond coat-top coat interface. Mixed failure modes comprising crack propagation through the bond coat-TGO interface, through TGO and within the top coat were identified. Based on the analysis of the experimental results and thorough discussion a novel design of microstructure for the high TCF performance columnar TBC is proposed. © 2017 Elsevier Ltd and Techna Group S.r.l.

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Air; Coatings; Engines; Gas turbines; Microstructure; Plasma jets; Plasma spraying; Sprayed coatings; Structural design; Suspensions (components); Thermal spraying, Columnar structures; Experimental investigations; High velocity air fuels; Physical vapor deposited; Suspension plasma spraying; Thermal cyclic fatigue; Thermal spray technology; Thermally grown oxide, Thermal barrier coatings
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-11920 (URN)10.1016/j.ceramint.2017.11.084 (DOI)000423891900070 ()2-s2.0-85034822127 (Scopus ID)
Available from: 2017-12-13 Created: 2017-12-13 Last updated: 2018-05-23Bibliographically approved
7. Tailoring columnar microstructure of axial suspension plasma sprayed TBCs for superior thermal shock performance
Open this publication in new window or tab >>Tailoring columnar microstructure of axial suspension plasma sprayed TBCs for superior thermal shock performance
2018 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 144, p. 192-208Article in journal (Refereed) Published
Abstract [en]

This paper investigates the thermal shock behavior of thermal barrier coatings (TBCs) produced by axial suspension plasma spraying (ASPS). TBCs with different columnar microstructures were subjected to cyclic thermal shock testing in a burner rig. Failure analysis of these TBCs revealed a clear relationship between lifetime and porosity. However, tailoring the microstructure of these TBCs for enhanced durability is challenging due to their inherently wide pore size distribution (ranging from few nanometers up to few tens of micrometers). This study reveals that pores with different length scales play varying roles in influencing TBC durability. Fracture toughness shows a strong correlation with the lifetime of various ASPS TBCs and is found to be the prominent life determining factor. Based on the results, an understanding-based design philosophy for tailoring of the columnar microstructure of ASPS TBCs for enhanced durability under cyclic thermal shock loading is proposed. © 2018 The Authors

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Coatings; Durability; Fracture toughness; Microstructure; Plasma jets; Plasma spraying; Pore size; Shock testing; Size distribution; Thermal shock; Thermal spraying, Columnar microstructures; Cyclic thermal shocks; Design philosophy; Different length scale; Strong correlation; Superior performance; Suspension plasma spraying; Thermal barrier coating (TBCs), Thermal barrier coatings
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-12192 (URN)10.1016/j.matdes.2018.02.011 (DOI)2-s2.0-85042178578 (Scopus ID)
Available from: 2018-03-05 Created: 2018-03-05 Last updated: 2018-05-23Bibliographically approved

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