Processes for preparing corrosion resistant coating systems for silicon-containing substrates

Abstract

Process includes providing a silicide-containing bond coat layer overlying a silicon-containing substrate, optionally forming a silica scale layer adjacent to and overlying the bond coat layer by preoxidizing the bond coat layer, and providing an environmental barrier coating overlying the bond coat layer. The environmental barrier coating includes a corrosion resistant outer layer formed by reacting a metal source with the silica scale layer, if present, or with the silicide-containing substrate in the absence of the silica scale layer. The process may include providing a thermal barrier coating overlying the corrosion resistant outer layer. The silicon-containing substrate may include at least a portion of a gas turbine engine component selected from a turbine blade, vane, and blisk.

1 . A process comprising the following steps:
 (a) providing a silicon-containing substrate;   (b) providing a silicide-containing bond coat layer overlaying the substrate; and   (c) forming over the bond coat layer a corrosion resistant layer comprising corrosion resistant metal silicate   
     
     
         2 . The process according to  claim 1  wherein the corrosion resistant layer formed in (c) has a thickness up to about 5 mils. 
     
     
         3 . The process according to  claim 2  wherein step (c) is carried out by reacting a metal source and a silica source to form the corrosion resistant layer comprising a reaction-generated corrosion resistant metal silicate. 
     
     
         4 . The process according to  claim 3  further comprising:
 (d) prior to step (c), forming a silica scale layer on the surface of the bond coat layer.   
     
     
         5 . The process according to  claim 4  wherein in step (d), the silica scale layer is formed by preoxidizing a portion of the bond coat layer. 
     
     
         6 . The process according to  claim 3  wherein step (c) is carried out by reacting the metal source with a silica powder. 
     
     
         7 . The process according to  claim 3  wherein the metal source is a metal oxide. 
     
     
         8 . The process according to  claim 7  wherein the metal oxide is yttria. 
     
     
         9 . The process of  claim 1  wherein step (b) is carried out by: (1) depositing a corrosion resistant metal silicate powder from a slurry coating composition; and (2) heating the deposited powder to form the corrosion resistant layer. 
     
     
         10 . The process of  claim 1  wherein step (b) is carried out by plasma spraying the corrosion resistant layer. 
     
     
         11 . The process of  claim 10  wherein the corrosion resistant layer formed has a thickness up to about 30 mils. 
     
     
         12 . The process according to  claim 1  wherein step (a) includes providing a substrate forming at least a portion of a gas turbine engine component selected from a turbine blade, vane, and blisk. 
     
     
         13 . A process comprising:
 (a) providing a silicon-containing substrate;   (b) providing a silicide-containing bond coat layer overlaying the substrate, wherein the bond coat layer comprises a metal silicide selected from the group consisting of a silicide of chromium, tantalum, titanium, tungsten, zirconium, hafnium, a rare earth, and a compatible combination thereof; and   (c) forming over the bond coat layer an environmental barrier coating, wherein the environmental barrier coating includes a reaction-generated corrosion resistant metal silicate layer wherein the metal silicate is at least one member of the group consisting of a yttrium silicate, a scandium silicate, a zirconium silicate, a hafnium silicate, a rare earth silicate, and combinations thereof, and wherein a silicon source for the reaction-generated metal silicate includes an optional silica scale layer overlaying the bond coat layer, if present, or the silicide-containing bond coat layer in the absence of the silica scale layer.   
     
     
         14 . The process according to  claim 13  wherein in (a), providing the silicon-containing substrate includes pretreating the substrate prior to providing the bond coat layer in (b). 
     
     
         15 . The process according to  claim 13  wherein in (b), providing the bond coat layer includes depositing or forming the bond coat on a surface of the substrate by a technique selected from the group consisting of vapor phase deposition, pack cementation, high velocity oxy-fuel spray, plasma spray, physical vapor deposition, thermal spray, and chemical vapor deposition. 
     
     
         16 . The process according to  claim 13  including the silica scale layer, wherein the silica scale layer is formed by subjecting the silicide-containing bond coat layer to a temperature of from about 800° to about 1300° C. for from about 15 minutes to about 100 hours. 
     
     
         17 . The process according to  claim 13  further comprising:
 (d) providing a thermal barrier coating overlying the corrosion resistant outer layer.   
     
     
         18 . The process according to  claim 13  wherein in (a), providing a substrate includes providing a substrate forming at least a portion of a gas turbine engine component selected from a turbine blade, vane, and blisk. 
     
     
         19 . A process comprising:
 (a) providing a silicon-containing substrate;   (b) providing a silicide-containing bond coat layer overlying the substrate;   (c) forming a silica scale layer adjacent to and overlying the bond coat layer by preoxidizing a portion of the bond coat layer under conditions sufficient to provide the silica scale layer with a thickness of from about 0.5 to about 50 microns;   (d) providing an environmental barrier coating overlying the bond coat layer, wherein providing the environmental barrier coating includes forming a corrosion resistant outer layer adjacent to and overlying the silica scale layer by reacting a metal source with the silica scale layer; and   (e) providing a thermal barrier coating overlying the corrosion resistant outer layer.   
     
     
         20 . The process according to  claim 19  wherein in (a), providing a substrate includes providing a substrate forming at least a portion of a gas turbine engine component selected from a turbine blade, vane, and blisk.