Thermal Stability of Air Plasma Spray and Solution Precursor Plasma Spray Thermal Barrier Coatings

Abstract

Yttria‐stabilized zirconia (7YSZ) thermal barrier coatings (TBCs) were produced by conventional air plasma spray (APS) and solution precursor plasma spray (SPPS) processes. Both TBCs were isothermally heat treated from 1200° to 1500°C for 100 h. Changes in the phase content, microstructure, and hardness were investigated. The nontransformable tetragonal (t′) phase is the predominant phase in both the as‐sprayed APS and SPPS TBCs. APS and SPPS coatings exhibit similar thermal stability behavior such as densification rate, hardness increase, and grain coarsening rate. Both the as‐received and heat‐treated APS and SPPS TBCs show a bimodal pore size distribution with nano‐ and micro‐size pores. After 1400°C/100 h heat treatment, equiaxed grains replace the columnar structure in APS TBCs and the splat structure disappears. Vertical cracks remain after the 1500°C/100 h exposure in SPPS TBCs. The monoclinic phase appears in APS TBCs after a 1400°C/100 h exposure and in SPPS coatings after a 1500°C/100 h exposure.

Microstructure analyses and thermophysical properties of nanostructured thermal barrier coatings

“…The result reveals a bimodal pore size distribution, similar to that in the conventional zirconia coatings. 24,25 Micropores contribute a larger percentage of the total porosity than macropores. The fine micropores, with diameters smaller than 1 lm, include intrasplat microcracks, intersplat gaps resulted from poor adhesion, and small voids originated from the unmelted particles.…”

Thermal Aging Behavior of Axial Suspension Plasma-Sprayed Yttria-Stabilized Zirconia (YSZ) Thermal Barrier Coatings

“…Typically, state-of-the-art TBCs present the duplex layer structure consisting of an oxidation-resistant metallic bond coat and a heat-insulating ceramic top-coat deposited either by atmospheric plasma spraying (APS) or electron beam-physical vapor deposition (EB-PVD) (Ref 3). 6-8 wt.% Y 2 O 3 -partially stabilized ZrO 2 (6)(7)(8) is the most widely applied material for fabricating the ceramic top-coat not only because of its low high-temperature thermal conductivity, but also because it has a high coefficient of thermal expansion (CTE) close to that of the metallic substrate ( Ref 1,4). Based on the process development in the past decades, further reduced thermal conductivity of actual YSZ coatings can be obtained by APS process, due to which the APS coatings have the following favorable microstructural characteristics of layered and porous microstructures with inter-splat pores and microcracks aligned parallel to the top-coat/bond-coat interface.…”

“…As we know, the increased operational temperature of gas turbines will necessitate the demand to find coatings enabling better thermal insulation with high strain tolerance. Recently, much effort has been devoted to evaluate the solution precursor plasma-sprayed (SPPS) or suspension plasma-sprayed (SPS) TBCs with the unique microstructure of vertical cracks in a porous matrix and substantially equiaxed grains (Ref [7][8][9]. We note that the SPPS or SPS TBCs have initially favorable microstructures which combined the high thermal insulating property of the APS coatings and high strain tolerance of the EB-PVD coatings.…”

The Solution Precursor Plasma Spray Coatings: Influence of Solvent Type

“…Solution Precursor Plasma Spray (SPPS) process has been successfully developed to deposit YSZ-based TBCs with excellent durability as well as to deposit dense coatings [1][2][3][4][5][6][7]. In the SPPS process, an aqueous solution precursor, instead of the conventional powder feedstock, is injected into the plasma jet.…”