The key process parameters influencing formation of columnar microstructure in suspension plasma sprayed zirconia coatings

Abstract

The paper discusses the screening of experimental variables leading to formation of a columnar microstructure in suspension plasma sprayed zirconia coatings. These variables tested in 12 experimental runs included: (i) 2 types of zirconia powder; (ii) 4 concentration of solids in suspensions; (iii) 4 substrate preparation methods; and (iv) 2 plasma spray setups. Two different, commercially available, powders were used to formulate the suspensions. Yttria and ceria stabilized zirconia of composition ZrO 2 + 24 wt.% CeO 2 + 2.5 wt.% Y 2 O 3 (YCSZ) was milled the decrease the particles sizes. The yttria stabilized zirconia of composition ZrO 2 + 14 wt.% Y 2 O 3 (14YSZ) was used as received. The coatings were deposited on 304L stainless steel substrates which had the surface prepared by: (i) grid blasting; (ii) grinding; (iii) turning; and (iv) laser treatment. The 3D topographies of substrates' surfaces were characterized and their roughnesses were measured. The suspensions were plasma sprayed using the following plasma torches: SG-100 of Praixair and Triplex of Sulzer-Metco. The microstructure of powders and coatings was analyzed by optical microscopy, scanning electron microscopy (SEM) and field emission scanning electron microscopy (FE-SEM) as well as by X-ray diffraction. The columnar microstructure was formed in coatings sprayed with both plasma setups sprayed using finer 14YSZ powder suspensions. The substrate surface preparation as well as low concentration of solids in suspension promoted their formation. Rietveld method was applied to determine the quantity of different phases in the structure of coatings and to calculate the lattice parameters. The YCSZ coatings crystallized in mainly tetragonal phase with a small content of monoclinic phase. The 14YSZ crystallized in cubic phase. Finally, the thermal diffusivity of coatings was characterized up to 523 K with the use of laser flash method and thermal conductivities of coatings were determined. The conductivities were in the range from 0.6 to 1.1 W/(mK) depending on temperature for YCSZ and 14YSZ coatings.

Thermal conductivity and thermal cyclic fatigue of multilayered Gd2Zr2O7/YSZ thermal barrier coatings processed by suspension plasma spray

“…Thermal conductivity of YSZ obtained in this work was similar to the trend reported by Pawlosky et al [42] & Curry et al [37,43] on suspension plasma sprayed YSZ coatings. In the case of standard APS sprayed YSZ, thermal conductivity decreases with increase in temperature up to 800ºC and then begins to increase due to sintering effects.…”

Computational image analysis of Suspension Plasma Sprayed YSZ coatings

“…As already proven [1,8], different scaled porosity can be observed. In general, many characterization techniques may be used for porosity analysis.…”

“…Consequently, all parameters were individually set for WSP-H 500 and Axial III. The aimed thickness of both kinds of YSZ coatings was 150 µm [8]. …”

“…However, on the other hand, the final coating's properties are highly dependent on the deposition parameters. APS spraying is already known to have 50 variables [4], but SPS method is even more complex (for example, the suspension properties highly influence process characteristics) [5][6][7][8]. Therefore, in this work, two types of SPS coatings with different microstructures (porous and dense) are investigated.…”

Aqueous suspension processing of multicomponent submicronic Y-TZP/Al 2 O 3 /SiC particles for suspension plasma spraying

“…Since the suspensions to be used for SPS can present relatively low solids content due to the viscosity limitations imposed by the suspension injection system [3,33], SPS suspension viscosity can be very low and subjected to a large measurement error. In order to optimise the rheological behaviour, it was preferable to prepare concentrated suspensions with 30 vol.% solids in order to unequivocally detect the best dispersing conditions in terms of deflocculant content and sonication time.…”