Solution precursor spraying is a new method of applying thermal barrier coatings (TBCs) on metallic substrates.
In this work, the injection of a solution precursor has been made axially into an oxy-acetylene
flame to deposit 7 wt.% yttria stabilized zirconia (7 wt.% YSZ) coatings. For this purpose a home-made atomizer
has been inserted into the nozzle of a flame spray torch. The precursor used was an aqueous solution containing
zirconium and yttrium salts to make a solid solution of 93 wt.% ZrO2 and 7 wt.% Y2O3 (7YSZ) in the coating. A
martensitic stainless steel plate has been used as substrate on which a bond coat of NiCrAlY alloy was applied
by atmospheric plasma spray process. The effects of spray distance and atomizing gas (oxygen and hydrogen)
on the microstructure, phase composition, thermal shock and thermal exposure resistance of the coatings
have been examined. The results show that the use of H2 as the precursor atomizing gas instead of oxygen increases
the enthalpy of the flame the result of which is coatings with the least non decomposed precursor and
highest crystalline YSZ. This effect causes the severe cracking at thermal shock and thermal exposure tests in
coatings made by oxygen atomizing due to higher amount of non-decomposed precursor. By contrast, coatings
made by hydrogen atomizing showed very little cracking because of increased enthalpy of the flame and a small
quantity of non-decomposed precursor