Evaluation of Microstructure and Hot Corrosion Behaviour of YPSZ / Al2O3Composite Plasma Sprayed Coatings at 900oc by Molteneutectic vana- date-SulfateSalt

Abstract

This work is aimed to study effect of alumina coating on the partially stabilized zirconia alumina composite (YPSZ/ Al2O3) on the microstructure, phase transformation and hot corrosion perfor- mance of eutectic molten salt V2O5 + 45 wt% Na2SO4 and comparing with conventional YSZ.Both the pure alumina and YPSZ are sprayed by using atmospheric plasma spray APS. Hot corrosion for composite is done by exposing the samples to an isothermal air furnace testing at900 °C for different exposure times of40 and 80 hours. Upper surface plan views of the coatings are exam- ined using SEM. The hot corrosion test products are determined using EDS, EPMA and XRD. The results indicate the higher hot corrosion resistance of YSZ/ Al2O3 composite coatings compared with conventional YSZ sprayed coatings. Degradation of YSZ due to the presence of eutectic harsh salt attack is occurred by destabilization of yttria from the zirconia yttria coatings. This will lead to disrupt transformation from metastable tetragonal phase (t’) to monoclinic phase (m). the corrosion products of YVO4produce by leaching process. During exposure the composite to the molten salt the Al2O3is reacted with vanadate to form a low-melting liquid eutectic phase, lead- ing to dissolution of Al2O3in molten NaVO3Na2O–V2O5–Al2O3. The pores and cracks within the YSZ coating are filled with Al2O3. The absences of leaching of yttria in under layer for composite coatings is related to the absence of pockets of open porosity and cracks due to elimination after alumina layer applied.