Methods for preparing thermal barrier coatings with high fracture toughness inner layer for improved impact resistance

Abstract

Method for preparing reduced thermal conductivity thermal barrier coating having improved impact resistance for an underlying substrate for high temperature applications. An exemplary method includes depositing a first zirconia-containing ceramic composition having a c/a ratio of about 1.011 to about 1.016 and stabilized in the tetragonal phase by yttria, calcia, ceria, scandia, magnesia, india, lanthana, gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, europia, praseodymia, and mixtures thereof, and including about 0.3 to about 0.5% by weight lanthana, neodymia, gadolinia, and mixtures thereof The first material forms a high fracture toughness inner layer having a fraction of porosity of about 0.20 or less, and a thickness in the range of from about 0.5 to about 2 mils. The method includes depositing a ceramic material forming an outer thermal insulating layer overlying the inner layer and having a greater fraction of porosity than the inner layer.

1 . A method comprising:
 a) optionally providing a bond coat layer on at least a surface of a metallic substrate;   b) depositing on the bond coat layer, or on the surface of the substrate in the absence of the bond coat, a first material comprising a zirconia-containing ceramic composition having a c/a ratio of the zirconia lattice in the range of from about 1.011 to about 1.016 and stabilized in the tetragonal phase by a stabilizing amount of a stabilizing metal oxide selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india, lanthana, gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, europia, praseodymia, and mixtures thereof, and comprising from about 0.3 to about 0.5% by weight of a metal oxide selected from the group consisting of lanthana, neodymia, gadolinia, and mixtures thereof, wherein the first material is able to form a high fracture toughness inner layer, wherein depositing the first material includes controlling deposition conditions so that the inner layer formed thereby comprises a fraction of porosity of about 0.20 or less, and a thickness in the range of from about 0.5 to about 2 mils; and   c) depositing on the inner layer a second material comprising a ceramic thermal barrier coating material able to form an outer thermal insulating layer, wherein depositing the second material includes controlling the deposition conditions so that the outer layer formed thereby has a greater fraction of porosity than the fraction of porosity of the inner layer; wherein the inner fracture toughness layer and the outer thermal insulating layer provide a thermal barrier coating for the substrate.   
     
     
         2 . The method according to  claim 1  wherein in (c), the second material is deposited so as to provide the outer layer with a thickness comprising about 50 to about 95% of a thickness of the thermal barrier coating. 
     
     
         3 . The method according to  claim 1  wherein in (b), depositing the first material includes utilizing a physical vapor deposition process. 
     
     
         4 . The method according to  claim 1  wherein in (c), depositing the second material includes utilizing a physical vapor deposition process. 
     
     
         5 . The method according to  claim 1  wherein in (c), the second material comprises at least one member of the group consisting of hydrated or unhydrated aluminum oxide, chemically phase-stabilized zirconia, and pyrochlores having a general formula A 2 B 2 O 7  where A is a metal having a valence of 3+ or 2+, and B is a metal having a valence of 4+ or 5+, where the sum of A and B is 7. 
     
     
         6 . The method according to  claim 1  wherein in (a), the bond coat layer comprises at least one member of the group consisting of an overlay bond coating including MCrAlY alloys, an overlay bond coating including NiAl(Zr), a diffusion coating including noble metal diffusion aluminides, and a diffusion coating including simple aluminides. 
     
     
         7 . A method comprising:
 providing a thermal barrier coating on an underlying metal substrate by:   a) forming an inner high fracture toughness layer overlaying the metal substrate, the inner layer having a fraction of porosity of about 0.20 or less, and a thickness in the range of from about 0.5 to about 2 mils, and sufficient to impart impact resistance to the thermal barrier coating, the inner high fracture toughness layer comprising a zirconia-containing ceramic composition having a c/a ratio of the zirconia lattice in the range of from about 1.011 to about 1.016 and stabilized in the tetragonal phase by a stabilizing amount of a stabilizing metal oxide selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india, lanthana, gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, europia, praseodymia, and mixtures thereof, and wherein the inner high fracture toughness layer comprises from about 0.3 to about 0.5% by weight of a metal oxide selected from the group consisting of lanthana, neodymia, gadolinia, and mixtures thereof, and   b) forming an outer thermal insulating layer overlying the inner layer and comprising a ceramic thermal barrier coating material.   
     
     
         8 . The method according to  claim 7  further comprising:
 providing a bond coat layer adjacent to and overlying the metal substrate prior to providing the thermal barrier coating.   
     
     
         9 . The method according to  claim 7  wherein in (a), forming the inner high fracture toughness layer includes utilizing a physical vapor deposition technique, and wherein in (b), forming the outer thermal insulating layer includes utilizing a physical vapor deposition technique to provide a strain-tolerant columnar structure of the thermal barrier coating. 
     
     
         10 . The method according to  claim 7  wherein the thermal barrier coating has a thickness of from about 1 to about 100 mils. 
     
     
         11 . The method according to  claim 7  further comprising:
 c) providing an intermediate section of the thermal barrier coating between the outer thermal insulating layer and the inner fracture toughness layer, wherein the intermediate section includes at least one other thermal insulating layer adjacent to and overlying the inner fracture toughness layer and at least one other fracture toughness layer adjacent to and overlying the at least one other thermal insulating layer.   
     
     
         12 . The method according to  claim 11  wherein in (c) providing the intermediate section of the thermal barrier coating includes utilizing a physical vapor deposition technique. 
     
     
         13 . A method for preparing a thermal barrier coating for an underlying metal substrate, the method comprising the steps of:
 a) forming an inner high fracture toughness layer overlaying the metal substrate, the inner layer having a fraction of porosity of about 0.20 or less, and a thickness in the range of up to about 5 mils, and sufficient to impart impact resistance to the thermal barrier coating, and comprising a zirconia-containing ceramic composition having a c/a ratio of the zirconia lattice in the range of from about 1.011 to about 1.016 and stabilized in the tetragonal phase by a stabilizing amount of a stabilizing metal oxide selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india, lanthana, gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, europia, praseodymia, and mixtures thereof, and wherein the inner layer comprises from about 2 to about 7% by weight hafnia, and wherein the inner layer comprises from about 0.3 to about 0.5% by weight of a metal oxide selected from the group consisting of lanthana, neodymia, gadolinia, and mixtures thereof, and   b) forming on the inner layer an outer thermal insulating layer adjacent to and overlying the inner layer and comprising a ceramic thermal barrier coating material.   
     
     
         14 . The method according to  claim 13  further comprising:
 c) providing an intermediate section of the thermal barrier coating between the outer thermal insulating layer and the inner fracture toughness layer, wherein the intermediate section includes at least one other thermal insulating layer adjacent to and overlying the inner fracture toughness layer and at least one other fracture toughness layer adjacent to and overlying the at least one other thermal insulating layer.   
     
     
         15 . A method for preparing a thermal barrier coating for an underlying metal substrate, the method comprising the steps of:
 a) forming an inner high fracture toughness layer overlaying the metal substrate, the inner layer having a fraction of porosity of about 0.20 or less, and a thickness in the range of up to about 5 mils, and sufficient to impart impact resistance to the thermal barrier coating, and comprising a zirconia-containing ceramic composition having a c/a ratio of the zirconia lattice in the range of from about 1.011 to about 1.016 and stabilized in the tetragonal phase by about 4 to about 7% by weight of a stabilizing metal oxide selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india, lanthana, gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, europia, praseodymia, and mixtures thereof, and wherein the inner layer includes at least one of hafnia or a metal oxide selected from lanthana, neodymia, gadolinia, and mixtures thereof, wherein if present, the hafnia is present in from about 2 to about 7% by weight, and wherein if present, the metal oxide is present in from about 0.3 to about 0.5% by weight; and   b) forming on the inner layer an outer thermal insulating layer adjacent to and overlying the inner layer and comprising a ceramic thermal barrier coating material.   
     
     
         16 . The method according to  claim 15  further comprising:
 c) providing an intermediate section of the thermal barrier coating between the outer thermal insulating layer and the inner fracture toughness layer, wherein the intermediate section includes at least one other thermal insulating layer adjacent to and overlying the inner fracture toughness layer and at least one other fracture toughness layer adjacent to and overlying the at least one other thermal insulating layer.