Microstructural studies on EB-PVD deposited NiCrAlY, YSZ and lanthanum zirconate for thermal barrier applications

Abstract

In this work, NiCrAl (BC), La2Zr2O7(TC), 7% YSZ (TC), two layer structure TBCs NiCrAl (BC) + 7%YSZ (TC) and NiCrAL (BC) + La2Zr2O7(TC) deposition by electron beam evaporation and microstructural investigation of the surface as well as cross sections is discussed. Nanocrystalline YSZ and La2Zr2O7 coating with desired microstructure is successfully deposited by electron beam evaporation at much lower substrate temperature 400 °C, as compared to high temperatures 700-800 °C used in many reported literature. The adhesion of YSZ and LZ with bond coated steel substrate was found to be very good. The e-beam evaporated films are dense with very fine grained (20 – 40 nm) morphology and have roughness varying from 3 to 9 nm. XRD analyses reveal the desired phase formations for the bond coats and the ceramic top coats (tetragonal and cubic phase of YSZ and pyrochlore phase of LZ). HRTEM studies on the cross sections show the formation of desired columnar growth with feather like structure with entangled columns in the films for thermal barrier applications. The interfaces of the films are found to be sharp and a 5 nm thick amorphous layer is detected between the steel substrate and bond coat.