{"id":8080,"date":"2026-03-16T13:35:46","date_gmt":"2026-03-16T11:35:46","guid":{"rendered":"https:\/\/teceudemo.com\/case-study-thermal-barrier-coatings\/"},"modified":"2026-05-21T15:44:46","modified_gmt":"2026-05-21T13:44:46","slug":"coatings-white-paper","status":"publish","type":"post","link":"https:\/\/www.tec-eurolab.com\/en\/coatings-white-paper\/","title":{"rendered":"Case study | Thermal Barrier Coatings"},"content":{"rendered":"

Thermal Barrier Coatings: mechanical characterization<\/h2>\n

Thermospraying: what is it<\/h2>\n

Thermospraying<\/strong> denotes a family of processes for deposition of thick coatings, metallic or nonmetallic. All techniques use a flashlight to heat the raw material, produced with the desired chemical composition, to a molten or semi-molten state and to project it to the substrate to be coated.<\/p>\n

The morphology of thermo-sprayed coatings is predominantly lamellar and results from the stacking of splats layer by layer, in a direction orthogonal to the surface of the component. Prior to any thermal spraying process, some roughness is always required on the surface in order to ensure better mechanical attachment to the coating. In fact, the thermo-sprayed particles, once they reach the substrate at a lower temperature, deform and may contract around the roughness ridges as they cool.
\nThermo-sprayed coatings typically contain: pores, partially melted or infused particles, splats (fully melted and deformed particles), metastable phases and (in the case of metallic coatings) oxide inclusions.<\/p>\n

The porosity of the coating is affected by the process parameters and the size of the raw material: starting with powders with a fine and sufficiently narrow particle size distribution (e.g., 5-22 \u03bcm), their melting is optimal and results in a dense coating, suitable for anti-wear and anti-corrosion applications. Conversely, coarse particles with wider distribution (e.g., 45-125 \u03bcm), with the same energy supplied to the gas jet, melt only partially and result in a porous coating, with worse mechanical properties but suitable for thermal insulation.<\/p>\n

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Fig. 1<\/figcaption><\/figure>\n
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Fig. 2<\/figcaption><\/figure>\n
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Fig. 3<\/figcaption><\/figure>\n

Case Study: Thermal Barrier Coatings<\/h2>\n

The object<\/h3>\n

Thermal Barrier Coatings (TBCs) are multi-layer, functional and protective coatings applied to metal substrates for the purpose of lowering surface temperature and slowing oxidation. The top layer is called the top coat<\/strong> and functions as a thermal insulator, while the intermediate bond coat<\/strong>, in addition to improving the adhesion of the top coat, provides good resistance to oxidation and corrosion at high temperature.<\/p>\n

Uses: burner liners, transition ducts and vanes in the early turbine stages (hot section) of turbogas units and aircraft engines.<\/p>\n

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Fig. 4<\/figcaption><\/figure>\n

Characterization techniques<\/h3>\n

1. Thermal conductivity test<\/h4>\n

The linear thermal gradient imposed by TBC is explained through the Fourier equation on heat conduction: Q=\u03bb*A*dT\/dX<\/strong><\/p>\n

It is noted that temperature reduction is more effective the lower the thermal conductivity of the material and the greater the thickness of the TBC. The substrate, generally consisting of Nickel-based superalloys (Inconel, Hastelloy, etc…), and the bond coat are made of metallic materials and make almost no contribution to thermal insulation. TBC enables substrate insulation due to its high porosity within the substrate and its low thermal conductivity as a ceramic.
\nReference Standard ASTM E1461<\/em>
\nConductivity is obtained indirectly from the formula: \u03bb=Cp*\u03c1*\u03b1<\/strong>
\nwhere Cp is specific heat, \u03c1 is density and \u03b1 is thermal diffusivity. The latter is usually measured by laser flash by heating the sample on one side only, inducing a temperature gradient.<\/p>\n

2. Tensile test or Adhesion test<\/h4>\n

The pull or bond test is a tensile test to measure the degree of internal cohesion of the coating and\/or the adhesion of the coating to the substrate. The bond strength value defines the integrity and durability of components coated by Thermal Spraying, which depend on both the internal cohesion between coating elements (layers and lamellae) and the adhesion at the interface between coating and substrate.
\nReference standard: ASTM C633-13
\nOnce the coating has been deposited onto a cylindrical specimen (\u201cbutton\u201d), both faces (top and bottom) are bonded to two cylindrical fixtures (loading fixtures) made of 1-inch diameter stainless steel. These are then subjected to a tensile test.
\nBreakage occurs at the weakest part of the specimen: if it is located at the interface between the substrate and the coating then an indication of the latter’s tensile adhesion is obtained, if it is located inside the coating then the bond strength value represents the degree of internal cohesion to the coating.<\/p>\n

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Fig. 5<\/figcaption><\/figure>\n
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Fig. 6<\/figcaption><\/figure>\n

3. Thermal cycling test<\/h4>\n

Thermal expansion and contraction induce stress at the interface between different materials and is one of the main causes of TBC failure. Indeed, at the interface with the TGO (Thermally Grown Oxide), generated by oxidation of the bond coat at the interface with the top coat, crack nucleation occurs in the direction parallel to the substrate, causing so-called coating spallation. In addition, at high temperature, the top coat undergoes sintering phenomena, which reduces its insulating capacity.
\nReference standard ISO 14188<\/em>
\nThe test is applied to measure the resistance to heating and cooling cycles.
\nUsually acceptability criteria are defined for this type of test based on visual analysis of the damage suffered by the coating (e.g., swelling, cracking, partial or total detachment of the coating).<\/p>\n

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Fig. 7<\/figcaption><\/figure>\n

Do you want to test the strength of your coatings?<\/h2>\n

Request information<\/p>\n","protected":false},"excerpt":{"rendered":"

Case study of mechanical characterization on thermospray coating of an aircraft turbine blade<\/p>\n","protected":false},"author":4,"featured_media":8063,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-8080","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/posts\/8080","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/comments?post=8080"}],"version-history":[{"count":3,"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/posts\/8080\/revisions"}],"predecessor-version":[{"id":14011,"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/posts\/8080\/revisions\/14011"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/media\/8063"}],"wp:attachment":[{"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/media?parent=8080"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/categories?post=8080"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.tec-eurolab.com\/en\/wp-json\/wp\/v2\/tags?post=8080"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}