Zirconia based coatings via chemical vapor deposition

This work was concerned with the production of ZrO₂ based coatings using chemical vapor deposition (CVD). Such coatings, produced by air plasma spray and electron beam physical vapor deposition (EBPVD), have seen use as thermal barrier coatings in gas turbine engines. The coatings which were examined were pure ZrO₂, Y₂O₃-stabilized ZrO₂ and alternating layers of ZrO₂ and Al₂O₂. The selection of Zr precursors for the deposition of ZrO₂ was addressed by studying the chlorination of metallic Zr, the vaporization of ZrCl₂₌₄ and the vaporization of Zr based metalorganics. Major parameters such as temperature. pressure and reactant flow rates were varied in an attempt to determine the optimum conditions for the deposition of ZrO₂ The effects of these parameters on the microstructure of the ZrO₂ deposits were studied. It was initially intended that once ZrO₂ was satisfactorily deposited, an Y based organometallic might be introduced along with the Zr precursor to stabilize the ZrO₂ In addition to the deposition of ZrO₂ and Y₂O₃-stabilized ZrO₂ coatings, the formation of a coating which consisted of alternating layers of ZrO₂ and Al₂O₃ was examined to determine the feasibility of and challenges associated with producing such a coating. It appeared that the chlorination of Zr provided the optimum precursor for the deposition of ZrO₂, The vaporization of ZrCl₄ typically resulted in clogged lines while the metalorganic chosen, zirconium tetramethyl heptadionate [Zr(tmhd)₄] resulted in coatings with undesirable characteristics. Also, it became evident that the deposition of Y₂O₃-stabilized ZrO₂ was much more difficult than first suspected. Effective parameters were difficult to determine. The Y₂O₃-stabilized ZrO₂ coatings that were produced appeared soft and seemed to be plagued by carbon contamination. Finally, a coating which consisted of alternating layers of ZrO₂ and Al₂O₃ was produced. The properties of this coating, however, have yet to be fully analyzed.