Composition, structure and properties of gradient thermal barrier coatings (TBCs) produced by electron beam physical vapor deposition (EB-PVD).

Abstract

Gradient thermal barrier coatings (TBCs) along with the bond coat were produced by one and the same technological cycle using electron beam physical vapor deposition (EB-PVD) of an MCrAlY ingot, then of an Al–Al 2O 3–ZrO 2(Y 2O 3) tablet (pressed multicomponent powder mixture) and finally of a ZrO 2–7 wt.% Y 2O 3 ceramic ingot. At the evaporation temperature used, vapor pressures of the tablet components decrease in the direction: Al→Al 2O 3→ZrO 2(Y 2O 3). The evaporation of these constituents also proceeds in the same order. As a result, a transition zone [with composition and structure gradients — transition gradient zone (TGZ)] — forms between the bond coat and outer ZrO 2–7 wt.% Y 2O 3 ceramic layer during deposition. The TGZ constitution and structure are primarily determined by the aluminum, Al 2O 3 and ZrO 2 contents of the tablet. As a consequence of liquid aluminum participation in the coating deposition process, a thin layer of β-phase (NiAl), smoothly transitions to an Al 2O 3 layer and then to ZrO 2–7 wt.% Y 2O 3.