Thermal barrier coating

摘要

A poorly conducting thermal barrier coating applied on a superalloy substrate comprises a mixture of oxides consisting of a composition based on zirconia, 3-15 weight % of an oxide, preferably yttria, that stabilizes the zirconia, 0.5-12 weight % of an additional metallic element selected from Ni, Co, Fe or a mixture of Ni and/or Co and/or Fe, or their oxides, and 0.02-0.1 weight % C. The homogeneous oxide mixture is deposited on the substrate by electron beam evaporation of a bar having a composition consisting of the above thermal barrier coating composition. The mixture can also be applied by thermal or plasma spraying, (plasma-assisted) chemical vapor deposition. A sublayer of nickel-aluminum alloy containing at least one metal selected from Cr, precious metals of crude platinum , yttrium and rare earths can be interposed between the substrate and the oxide mixture layer. Preferably the sublayer has formula MCrAlY, where M = at least one metal selected from Ni, Co and Fe. Independent claims are given for: (a) a superalloy metal piece whose surface is coated at least in part with the thermal barrier; and (b) a process for deposition of the thermal barrier on a superalloy substrate. The deposition process involves (i) mixing and sintering into the form of a bar a mixture of powders of zirconia, a zirconia-stabilizing oxide, and an element selected from Ni, Co and Fe; (ii) introducing the body to into an EB-PVD chamber previously loaded with the bar; and (iii) creating a vacuum in the chamber, preheating the substrate, and focussing an electron beam on the bar in order to vaporize the elements present in the bar so that they condense onto the substrate. In (i), mixing of the powders is achieved by using a binder comprising a solvent that is at least partially rich in carbon, preferably a polyvinyl alcohol. A thermally crackable, carbon precursor gas selected from methane, ethane, butane, propane, an alkene or alkyne, is introduced into the deposition chamber in the immediate vicinity of the substrate to be coated.