Abradable layer including a rare earth silicate

Abstract

An abradable coating may include a rare earth silicate. The abradable coating may be deposited over a substrate, an environmental barrier coating, or a thermal barrier coating. The abradable coating may be deposited on a gas turbine blade track or a gas turbine blade shroud to form a seal between the gas turbine blade track or gas turbine blade shroud and a gas turbine blade. The abradable coating may also include a plurality of layers, such as alternating first and second layers including, respectively, a rare earth silicate and stabilized zirconia or stabilized hafnia.

1 . A method comprising:
 depositing over a substrate of a blade track or a blade shroud a multilayer, porous abradable coating, wherein the multilayer, porous abradable coating comprises a plurality of layer pairs, and wherein each layer pair comprises a first layer including a rare earth silicate and a second layer including at least one of stabilized zirconia and stabilized hafnia; and   disposing at least one gas turbine blade comprising a blade tip relative to the blade track or the blade shroud so the blade tip contacts a portion of the multilayer, porous abradable coating during rotation of the gas turbine blade, and wherein the multilayer, porous abradable coating is configured to be abraded by the contact by the blade tip.   
     
     
         2 . The method of  claim 1 , further comprising:
 depositing over the substrate an environmental barrier coating (EBC) comprising at least one of mullite, barium strontium alumina silicate, barium alumina silicate, calcium alumina silicate, strontium alumina silicate, lithium alumina silicate, magnesium alumina silicate, or a rare earth silicate, and   wherein depositing over the substrate of the blade track or the blade shroud the multilayer, porous abradable coating comprises depositing over the EBC the multilayer, porous abradable coating.   
     
     
         3 . The method of  claim 2 , wherein depositing over the substrate the EBC comprises depositing over the substrate the EBC comprising the rare earth silicate. 
     
     
         4 . The method of  claim 1 , wherein the porous abradable coating comprises a first surface adjacent the substrate and a second surface opposite the substrate, and wherein depositing over the substrate of the blade track or the blade shroud the multilayer, porous abradable coating comprises, depositing over the substrate of the blade track or the blade shroud the multilayer, porous abradable coating including a first porosity of the multilayer, porous abradable coating proximate the first surface and a second, different porosity of the multilayer, porous abradable coating proximate the second surface. 
     
     
         5 . The method of  claim 4 , wherein the first porosity is less than the second porosity. 
     
     
         6 . The method of  claim 1 , wherein depositing over the substrate of the blade track or the blade shroud the multilayer, porous abradable coating comprises thermal spraying over the substrate the first layer comprising the rare earth silicate and a coating material additive. 
     
     
         7 . The method of  claim 6 , wherein the coating material additive comprises at least one of graphite, hexagonal boron nitride, and a polymer. 
     
     
         8 . The method of  claim 7 , wherein the coating material additive comprises polyester. 
     
     
         9 . The method of  claim 6 , further comprising subjecting the multilayer, porous abradable coating to a heat treatment. 
     
     
         10 . The method of  claim 9 , wherein subjecting the multilayer, porous abradable coating to the heat treatment at least one of burns and melts the coating material additive to form pores in the first layer. 
     
     
         11 . The method of  claim 1 , wherein at least one of the first layers of the multilayer, porous abradable coating comprises at least one of RE 2 SiO 5  and RE 2 Si 2 O 7 , and wherein RE is a rare earth element. 
     
     
         12 . The method of  claim 1 , wherein at least one of the first layers of the multilayer, porous abradable coating comprises a rare earth oxide. 
     
     
         13 . The method of  claim 1 , wherein at least one of the first layers of the multilayer, porous abradable coating comprises silica. 
     
     
         14 . The method of  claim 1 , wherein at least one of the first layers of the multilayer, porous abradable coating comprises at least one of alumina, Ta 2 O 5 , HfSiO 4 , an alkali oxide, and an alkali earth oxide. 
     
     
         15 . The method of  claim 1 , further comprising depositing over the substrate a bond coat, and wherein depositing over the substrate the EBC comprises depositing the EBC over the bond coat. 
     
     
         16 . The method of  claim 1 , further comprising depositing over the substrate a thermal barrier coating (TBC), and wherein depositing over the substrate of the blade track or the blade shroud the multilayer, porous abradable coating comprises depositing the multilayer, porous abradable coating over the TBC. 
     
     
         17 . The method of  claim 16 , further comprising depositing over the substrate a bond coat, and wherein depositing over the substrate the TBC comprises depositing over the bond coat the TBC. 
     
     
         18 . The method of  claim 1 , further comprising depositing over the substrate a bond coat, and wherein depositing over the substrate of the blade track or the blade shroud the multilayer, porous abradable coating comprises depositing over the bond coat the multilayer, porous abradable coating.