Sintering studies of plasma-sprayed zirconia

Eaton, Harry E.; Novak, Richard C.

doi:10.1016/0257-8972(87)90109-5

Cited by 68 publications

(32 citation statements)

References 7 publications

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“…The healing or the sintering process will lock the microstructure and hinder the sliding of splats as a strain accommodating mechanism, and thus result in sharp increase in stiffness after short heat treatment times. This is in agreement with previous observations for similar coatings [1,5,29,32]. The rate of sintering at a given temperature would depend on the diffusion coefficient, which is dependent on the dominant mechanism of mass transport (e.g., grain or grain boundary).…”

Section: Effect Of Service Conditionssupporting

confidence: 81%

“…They found that microcrack healing and locking together of overlapping splats via diffusion and grain growth across splat boundaries are the two major sintering mechanisms. Sharp changes in stiffness after short sintering times have also been observed by others [28][29][30]. While pronounced sintering of zirconia powders is not generally expected at temperatures below 1400 • C, detectable sintering effects have been reported in plasma-sprayed zirconia at temperatures as low as 800 • C [31].…”

Section: Sintering Effects On Young's Modulus Values Of Plasma Sprayementioning

confidence: 57%

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Stiffness of Plasma Sprayed Thermal Barrier Coatings

Paul¹

2017

Coatings

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Thermal spray coatings (TSCs) have complex microstructures and they often operate in demanding environments. Plasma sprayed (PS) thermal barrier coating (TBC) is one such ceramic layer that is applied onto metallic components where a low macroscopic stiffness favors stability by limiting the stresses from differential thermal contraction. In this paper, the Young's modulus of TBC top coat, measured using different techniques, such as four-point bending, indentation and impulse excitation is reported, along with a brief description of how the techniques probe different length scales. Zirconia-based TBC top coats were found to have a much lower global stiffness than that of dense zirconia. A typical value for the as-sprayed Young's modulus was~23 GPa, determined by beam bending. Indentation, probing a local area, gave significantly higher values. The difference between the two stiffness values is thought to explain the wide range of TBC top coat Young's modulus values reported in the literature. On exposure to high temperature, due to the sintering process, detached top coats exhibit an increase in stiffness. This increase in stiffness caused by the sintering of fine-scale porosity has significant impact on the strain tolerance of the TBC. The paper discusses the different techniques for measuring the Young's modulus of the TBC top coats and implications of the measured values.

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Section: Effect Of Service Conditionssupporting

confidence: 81%

Section: Sintering Effects On Young's Modulus Values Of Plasma Sprayementioning

confidence: 57%

Stiffness of Plasma Sprayed Thermal Barrier Coatings

Paul¹

2017

Coatings

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“…The effect of different values of E av is investigated here, but its value is assumed to remain constant during sintering. This is a limitation of the current formulation, since it is known that the stiffness tends to increase during sintering [18][19][20][21][22][23].…”

Section: Model Geometrymentioning

confidence: 99%

A sintering model for plasma-sprayed zirconia thermal barrier coatings. Part II: Coatings bonded to a rigid substrate

2009

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The sintering model described in Part I, which relates to free-standing plasma-sprayed thermal barrier coatings, is extended here to the case of a coating attached to a rigid substrate. Through-thickness shrinkage measurements have been carried out for coatings attached to zirconia substrates, and these experimental data are compared with model predictions. The model is then used to explore the influence of the substrate material (zirconia vs. a nickel superalloy), and of the in-plane coating stiffness. Both differential thermal expansion stresses and tensile stresses arising from the constraint imposed on in-plane shrinkage can be relaxed via two diffusional mechanisms: Coble creep and microcrack opening. This relaxation allows progression towards densification, although the process is somewhat inhibited, compared with the case of a free-standing coating. Comparison of the stored elastic strain energy with the critical strain energy release rate for interfacial cracking allows estimates to be made of whether debonding is energetically favoured.

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“…The pore structure, in the form of inter-splat voids, intra-splat microcracks and other, coarser and more globular pores, has a strong influence on coating properties (see below). It is now well established (Ref [11][12][13][14][15][16]) that both the pore architecture and other microstructural features (grain size, phase constitution, etc.) of these coatings can be significantly affected by prolonged exposure to high temperature.…”

Section: Introductionmentioning

confidence: 99%

Effects of Impurity Content on the Sintering Characteristics of Plasma-Sprayed Zirconia

et al. 2007

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Yttria-stabilized zirconia powders, containing different levels of SiO 2 and Al 2 O 3 , have been plasma sprayed onto metallic substrates. The coatings were detached from their substrates and a dilatometer was used to monitor the dimensional changes they exhibited during prolonged heat treatments. It was found that specimens containing higher levels of silica and alumina exhibited higher rates of linear contraction, in both in-plane and through-thickness directions. The in-plane stiffness and the through-thickness thermal conductivity were also measured after different heat treatments and these were found to increase at a greater rate for specimens with higher impurity (silica and alumina) levels. Changes in the pore architecture during heat treatments were studied using Mercury Intrusion Porosimetry (MIP). Fine scale porosity (<$50 nm) was found to be sharply reduced even by relatively short heat treatments. This is correlated with improvements in inter-splat bonding and partial healing of intra-splat microcracks, which are responsible for the observed changes in stiffness and conductivity, as well as the dimensional changes.

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Sintering studies of plasma-sprayed zirconia

Cited by 68 publications

References 7 publications

Stiffness of Plasma Sprayed Thermal Barrier Coatings

Stiffness of Plasma Sprayed Thermal Barrier Coatings

A sintering model for plasma-sprayed zirconia thermal barrier coatings. Part II: Coatings bonded to a rigid substrate

Effects of Impurity Content on the Sintering Characteristics of Plasma-Sprayed Zirconia

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