Review on Advanced EB‐PVD Ceramic Topcoats for TBC Applications

Schulz, Uwe; Saruhan, Bilge; Fritscher, K.; Leyens, Christoph

doi:10.1111/j.1744-7402.2004.tb00182.x

Cited by 239 publications

(104 citation statements)

References 48 publications

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“…Ceria evaporation from (Ce,Zr)O2 solid solutions is of particular interest since vapour pressures of CeO2 and ZrO2 are known to differ by 5 orders of [38] and mass loss of Ce 0.85 Zr 0.15 O 2 (red) as a function of temperature at p total = 4 × 10 −9 bar; (b) Vapour pressures of various oxides as a function of the reciprocal temperature [43].…”

Section: Degradation Of (Cezr)o 2 Redox Ceramics By Selective Sublimmentioning

confidence: 99%

Ceria: Recent Results on Dopant-Induced Surface Phenomena

et al. 2017

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Abstract:Redox studies on dense zirconia-doped ceria pellets were carried out by thermogravimetric investigations and dilatometry. Up to 1600 K reduction parameters determined by both methods correspond to each other. At higher temperatures, however, thermogravimetry overestimates the degree of reduction since mass loss is not only due to oxygen exsolution but also to selective evaporation of CeO 2 whose vapour pressure is considerably higher than that of ZrO 2 . As a consequence surface segregation of zirconia occurs in (Ce,Zr)O 2−δ pellets leading to a porous surface zone of Ce 2 Zr 2 O 7 pyrochlore which gradually grows in thickness. Surface enrichment of zirconia is detrimental for splitting CO 2 or H 2 O since re-oxidation temperatures of (Ce,Zr)O 2−δ are known to be shifted towards lower temperatures with increasing ZrO 2 content. Thus, very harsh reduction conditions should be avoided for the (Ce,Zr)O 2−δ redox system. The kinetics investigations comprised the high temperature reduction step (T ∼ = 1600 K) and the "low" temperature oxidation reaction with a carbon dioxide atmosphere (T ∼ = 1000 K). The reduction kinetics (at around 1600 K and an oxygen activity of 7 × 10 −4 in the gas phase) directly yield the (reduction) equilibrium exchange rate of oxygen in the order of 10 −7 mol·O/(cm 3 ·s) as the kinetics are surface controlled. The oxidation step at around 1000 K, however, occurs in the mixed control or in the diffusion control regime, respectively. From oxygen isotope exchange in combination with SIMS depth profiling oxygen exchange coefficients, K, and oxygen diffusivities, D, were determined for so-called equilibrium experiments as well as for non-equilibrium measurements. From the obtained values for K and D the (oxidation) equilibrium exchange rates for differently doped ceria samples were determined. Their dependency on the oxygen activity and the nature and the concentrations of a tetravalent dopant (Zr) and trivalent dopants (La, Y, Sm) could be semi-quantitatively rationalised on the basis of a master equation for the equilibrium surface exchange rate.

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Section: Degradation Of (Cezr)o 2 Redox Ceramics By Selective Sublimmentioning

confidence: 99%

Ceria: Recent Results on Dopant-Induced Surface Phenomena

et al. 2017

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“…Subsequently, the vapor deposits onto a preheated substrate at a deposition rate of, typically, several µm/min. Due to the vapor phase condensation and shadowing effect [5], columnar-structured TBCs with a high level of strain tolerance can be achieved [6]. However, the high manufacturing cost limits the use of EB-PVD on severe thermo-mechanically loaded parts, such as first-row blades.…”

Section: Introductionmentioning

confidence: 99%

Development of YSZ Thermal Barrier Coatings Using Axial Suspension Plasma Spraying

2017

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Abstract:The axial injection of the suspension in the atmospheric plasma spraying process (here called axial suspension plasma spraying) is an attractive and advanced thermal spraying technology especially for the deposition of thermal barrier coatings (TBCs). It enables the growth of columnar-like structures and, hence, combines advantages of electron beam-physical vapor deposition (EB-PVD) technology with the considerably cheaper atmospheric plasma spraying (APS). In the first part of this study, the effects of spraying conditions on the microstructure of yttria partially-stabilized zirconia (YSZ) top coats and the deposition efficiency were investigated. YSZ coatings deposited on as-sprayed bond coats with 5 wt % solid content suspension appeared to have nicely-developed columnar structures. Based on the preliminary results, the nicely developed columnar coatings with variations of the stand-off distances and yttria content were subjected to thermal cycling tests in a gas burner rig. In these tests, all columnar structured TBCs showed relatively short lifetimes compared with porous APS coatings. Indentation measurements for Young's modulus and fracture toughness on the columns of the SPS coatings indicated a correlation between mechanical properties and lifetime for the SPS samples. A simplified model is presented which correlates mechanical properties and lifetime of SPS coatings.

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“…Air plasma sprayed (APS) thermal barrier coatings (TBCs) are widely employed in the hot sections of industrial gas turbines to protect the underlying metallic components from high temperature, and to increase the efficiency of the turbines by enabling higher turbine inlet temperature [1][2][3][4][5]. It is well accepted that the surface roughness and aluminum supply in the bond coats are the most critical factors for the TBC's durability.…”

Section: Introductionmentioning

confidence: 99%

Role of internal oxidation on the failure of air plasma sprayed thermal barrier coatings with a double-layered bond coat

Zou

Jia

Yang

et al. 2017

Surface and Coatings Technology

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Failure of air plasma sprayed (APS) thermal barrier coatings (TBCs) with a double-layered bond coat was investigated. The bond coat consists of a dense layer near the substrate side and a porous layer on the surface. Both were made of NiCoCrAlY alloy and deposited using high velocity oxygen-fuel technique. After thermal cycling, a large amount of internal oxides formed (up to 45% in volume fraction), introducing a significant volume expansion both in in-plane and perpendicular direction in the bond coat. However, the presence of the ceramic top coat can suppress the bond coat in-plane swelling thus lowering the internal oxidation rate.Compared with the fully dense bond coat, the interface roughness of the porous bond coat increases significantly when internal oxidation occurs. There is a strong correlation between the internal oxidation and the interface roughness. In addition, both the beneficial and detrimental effects of internal oxidation on TBC failure were discussed. It is proposed that a fully dense bond coat with a proper surface roughness should have a longer thermal cycling

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Review on Advanced EB‐PVD Ceramic Topcoats for TBC Applications

Cited by 239 publications

References 48 publications

Ceria: Recent Results on Dopant-Induced Surface Phenomena

Ceria: Recent Results on Dopant-Induced Surface Phenomena

Development of YSZ Thermal Barrier Coatings Using Axial Suspension Plasma Spraying

Role of internal oxidation on the failure of air plasma sprayed thermal barrier coatings with a double-layered bond coat

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