Coatings with Columnar Microstructures for Thermal Barrier Applications

Abstract

Columnar-structured thermal barrier coatings (TBCs) manufactured by electron beam-physical vapor deposition (EB-PVD) are well known to exhibit high strain tolerance. However, as EB-PVD is a high-vacuum process, it is expensive. Suspension plasma spraying (SPS) and plasma spray-physical vapor deposition (PS-PVD) are alternatives for the manufacture of similar microstructures. Herein, the state of the art of manufacturing columnar-structured TBCs by SPS and PS-PVD is outlined. Both processes have been investigated and further developed at Forschungszentrum Jülich for many years. The mechanisms leading to the formation of columnar-structured coatings are described and differentiated from EB-PVD. Examples are given for SPS and PS-PVD columnar microstructures and their life performance.

Critical Raw Materials Saving by Protective Coatings under Extreme Conditions: A Review of Last Trends in Alloys and Coatings for Aerospace Engine Applications

“…The increasing demand for new functional coatings has been a strong incentive for research, not only towards understanding the fundamentals and technical aspects of film nucleation and growth, but also towards developing new deposition techniques allowing for a better control of the deposition process [ 132 ]. EB-PVD, powder flame spraying, plasma thermal spray, cold gas dynamic spray coating, sputtering and CVD (Chemical Vapor Deposition) are techniques suited for creating different types of TBCs [ 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 ]. Actually, EB-PVD and APS are the most widely used techniques for obtaining TBCs and different multilayer coatings from a large class of different materials.…”

Tuning the Microstructure and Thickness of Ceramic Layers with Advanced Coating Technologies Using Zirconia as an Example

“…In modern gas turbines, for example, in aircraft engines, gas turbine engines on ships, and land-based industrial gas turbine engines, TBC systems are used to improve efficiency and/or component durability. [37] YSZ is ideally suited for TBC applications due to its high melting point, phase stability, low thermal conductivity, chemical inertness, and good thermal expansion match with the bond coat material (a matching component between the base material and the top coat). [38] YSZ with 6-8 wt% yttria has become a standard TBC material, with early developments dating back to the 1980s.…”

“…Shadowing occurs due to the interaction between surface roughness and the angular directions of arriving particles, thus generating columns that are separated by gaps. [242] A small ratio of splat size to surface asperity size favors column formation. Such an effect can be used to tailor microstructures of SPS coatings that range from dense vertically cracked to columnar microstructures.…”

Microcrack propagation induced by dynamic infiltration of calcium-magnesium-alumino-silicate in columnar structures for thermal barrier coatings

“…HCMAS0 is the height of deposition on the surface of the TBC (i.e., on top of the TC), and HCMAS is the depth of the CMAS infiltration induced by the infiltration of CMAS into the column gaps of the columnar-structured TBCs. The depth of the substrate is set to HSUB = 300 mm, and the layer thicknesses are HTC = HBC = 100 μm [4,26] and HCMAS0 = 20 μm [14]. To determine the influence of a crack by dynamic CMAS infiltration, a microcrack of length 2a with an angle of inclination  with respect to the x-axis with a depth of HCRACK, which is measured from the CMAS0/TC interface to the crack center, was preassigned in the YSZ #6 column, as shown in Fig.…”

“…On the other hand, electron beam-physical vapor deposition (EB-PVD) is known as high strain tolerance owing to the specific columnar microstructure. Beside EB-PVD, suspension plasma spraying (SPS) and plasma sprayphysical vapor deposition (PS-PVD) are alternative methods for the columnar structure [4].…”