Effect of fructose-containing feedstocks on the microstructure of multicomponent coatings deposited by suspension plasma spraying

Abstract

This work addressed to investigate the use of fructose as an ingredient in the feedstock suspension of a Y-TZP/Al2O3/SiC multicomponent coating manufactured by SPS. The effect on suspension rheology and resulting coatings microstructure and thermal conductivity was assessed. It was observed that addition of fructose hardly affected the rheological behaviour of the suspensions while a strong decrease in the surface tension of water occurred. Drastic changes of coating microstructures were attributed to this effect in liquid surface tension i.e. fructose favoured the growth of columnar structure in the coatings. XRD patterns showed that fructose increased the crystallinity of the tetragonal Y-TZP phase of the coatings. The determination of thermal conductivity showed that the formation of a controlled columnar structure along with porosity is beneficial for thermal insulation. The results show, for the first time, the designing of coatings with columnar microstructure by SPS from water-based suspension feedstocks.

Modification of the Properties of Al2O3/TZ-3YS Thermal Barrier Coating by the Addition of Silicon Carbide Particles and Fructose

“…The average particle sizes (d 50 ) of α-Al 2 O 3 , TZ-3YS and α-SiC were 0.5, 0.4 and 0.6 µm, respectively. More details about the raw materials and suspension preparation are described in previous work [7,9]. A total of three suspensions were prepared: Al 2 O 3 /TZ-3YS suspension in a eutectic ratio (60/40 wt.%); Al 2 O 3 /TZ-3YS suspension with a 15 wt.% SiC that acts as reinforcement agent; and Al 2 O 3 /TZ-3YS suspension with SiC using the same ratio but adding 20 wt.% D-fructose (AppliChem GmbH, Darmstadt, Germany) that acts as an additive to modify the suspension rheology and surface tension, according to a previous work by the authors [7].…”

“…AISI type 304 stainless steel was used as substrate, which was grit-blasted using black corundum until a surface roughness (Ra) of 2.2 ± 0.1 µm was reached and then cleaned with ethanol. A NiCoCrAlTaY superalloy (Amdry 997, Oerlikon-Metco, Salzgitter, Germany) was deposited as a bond coat by atmospheric plasma spraying [7]. The deposition parameters, which are shown in Table 1, were selected from previous research [10].…”

“…When aqueous suspensions are used, one possibility to improve the feedstock is to increase the solid loading due to high heat requirements to evaporate the water [4]. An alternative route involves the use of additives like fructose, which reduces the viscosity and surface tension so the formed droplet inside the plasma plume is smaller, and it eases solvent evaporation and solid melting [7].…”

“…SiC exhibits two functions: mechanical reinforcement and self-healing. The self-healing effect by oxidation of SiC can increase the TBC's lifetime, but it will be extensively studied in future work [7,8]. The problem of adding SiC is the capacity heat.…”

“…The problem of adding SiC is the capacity heat. To solve this problem, suspensions with high solid-loading were prepared, and new additives, like fructose, were evaluated [7]. In a previous work, it was found that fructose modified the microstructure of the coatings.…”