AN INVESTIGATION ON EFFECT OF BOND COAT REPLACEMENT ON HOT CORROSION PROPERTIES OF THERMAL BARRIER COATINGS

In the present study NiCrAlY bond coating layer was produced by electroplating against common atmospheric plasma spraying (APS). Both types of the bond coats were applied on IN۷۳۸LC base metal then, the YSZ (ZrO۲-۸% Y۲O۳) thermal barrier top layer was coated by atmospheric plasma spray technique. Hot corrosion is one of the main destructive factors in thermal barrier coatings (TBCs) which come as a result of molten salt effect on the coating–gas interface. In this investigation the hot corrosion behavior of coatings was tested in the furnace which was contain Na۲SO۴-۵۵% V۲O۵ and mixed salts environment at ۹۰۰°C up to ۱۵ hr. dwell time. Optical microscopy, scanning electron microscopy (SEM / EDS) and X-ray diffraction analysis (XRD) was used to determine the crystallographic structure and phase transformation of the coatings before and after the hot corrosion tests. The transformation of tetragonal Zirconia to monoclinic ZrO۲ and formation of YVO۴ crystals as hot corrosion products caused the degradation of mentioned TBCs. The results showed NiCrAlY coated by economical electroplating method a viable alternative for common thermals sprayed bond coats in hot corrosive environments with same corrosion behavior

Keywords:

Electroplating , Atmospheric Plasma Spraying , NiCrAlY bond coat , Thermal barrier coatings , YSZ , Hot