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Influence of microstructure on thermal cycling lifetime, thermal insulation, and mechanical properties of yttria-stabilized zirconia thermal barrier coatings
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). Scania CV AB. (System- och komponentdesign)ORCID iD: 0000-0002-3423-8688
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). (System- och komponentdesign)ORCID iD: 0000-0003-2489-0688
(English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347Article in journal (Refereed) Submitted
Abstract [en]

Thermal barrier coatings (TBCs) may improve the fuel efficiency of heavy-duty diesel engines by reducing heat losses. A combination of durability, low thermal conductivity, and high reflectance is required for a TBC in the combustion chamber. These properties are evaluated for yttria-stabilized zirconia coatings, produced using atmospheric plasma spraying (APS) and plasma spray–physical vapour deposition (PS-PVD). The influences of different types of microstructure and reflective metallic coatings on the surface are studied. APS coatings with segmentation cracks and PS-PVD coatings with columnar microstructure have the best thermal cycling lifetime, while nanostructured and conventional APS coatings have the lowest thermal conductivities. The nanostructured APS coating has the highest reflectance at low temperatures, while the columnar PS-PVD coating has the highest reflectance at elevated temperatures. It is further demonstrated that a thin silver layer improves the reflectance of a dense, segmented APS YSZ coating.

National Category
Mechanical Engineering
Research subject
Machine Design
Identifiers
URN: urn:nbn:se:kth:diva-212496OAI: oai:DiVA.org:kth-212496DiVA, id: diva2:1135078
Note

QC 20170822

Available from: 2017-08-22 Created: 2017-08-22 Last updated: 2017-08-22Bibliographically approved
In thesis
1. Thermal Barrier Coatings for Diesel Engines
Open this publication in new window or tab >>Thermal Barrier Coatings for Diesel Engines
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Reducing the heat losses in heavy-duty diesel engines is of importance for improving engine efficiency and reducing CO2 emissions. Depositing thermal barrier coatings (TBCs) onto engine components has been demonstrated to have great potential to reduce heat loss from the combustion chamber as well as from exhaust components. The overall aim of this thesis is to evaluate the thermal cycling lifetime and thermal insulation properties of TBCs for the purpose of reducing heat losses and thermal fatigue in heavy-duty diesel engines.

In the thermal cycling test inside exhaust manifolds, nanostructured yttria-stabilized zirconia (YSZ) performed best, followed by YSZ with conventional microstructure and then La2Zr2O7. Forsterite and mullite could not withstand the thermal cycling conditions and displayed large cracks or spallation. Two sol-gel composite coatings displayed promising thermal cycling performance results in a furnace test under similar conditions.

Thermal cycling testing of YSZ coatings having different types of microstructure, in a furnace at temperatures up to 800°C, indicated that the type of microstructure exerted a great influence. For the atmospheric plasma sprayed coatings, a segmented microstructure resulted in the longest thermal cycling lifetime. An even longer lifetime was seen for a plasma spray–physical vapour deposition (PS-PVD) coating.

In situ heat flux measurements inside the combustion chamber indicated that plasma-sprayed Gd2Zr2O7 was the TBC material providing the largest heat flux reduction. This is explained by a combination of low thermal conductivity and high reflectance. The plasma-sprayed YSZ and La2Zr2O7 coatings provided very small heat flux reductions. Long-term testing indicated a running-in behaviour of YSZ and Gd2Zr2O7, with a reduction in heat flux due to the growth of microcracks in YSZ and the growth of macrocracks in Gd2Zr2O7.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. p. 45
Series
TRITA-MMK, ISSN 1400-1179 ; 2017:11
Keywords
thermal barrier coatings, diesel engine, thermal cycling fatigue, heat flux, running-in, exhaust manifolds, yttria-stabilized zirconia, gadolinium zirconate, lanthanum zirconate
National Category
Mechanical Engineering
Research subject
Machine Design
Identifiers
urn:nbn:se:kth:diva-212298 (URN)978-91-7729-475-7 (ISBN)
Presentation
2017-09-08, B242, Brinellvägen 83, Stockholm, 13:00 (Swedish)
Opponent
Supervisors
Note

QC 20170821

Available from: 2017-08-22 Created: 2017-08-17 Last updated: 2017-08-22Bibliographically approved

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