Nickel aluminide coating and coating systems formed therewith

Abstract

A beta-phase NiAl overlay coating containing a dispersion of ceramic particles and a process for depositing the overlay coating. If the coating is used to adhere a thermal barrier coating (TBC), the TBC exhibits improved spallation resistance as a result of the dispersion of ceramic particles having a dispersion-strengthening effect on the overlay coating. The overlay coating contains at least one reactive element and is deposited so that the some of the reactive element deposits as the ceramic particles dispersed in the overlay coating.

1 . A process of depositing a coating system on a superalloy substrate, the coating system comprising a beta-phase NiAl intermetallic overlay coating containing at least one reactive element, the process comprising the step of depositing the overlay coating by a physical vapor deposition or thermal spray deposition so that during deposition at least some of the at least one reactive element is reacted to form ceramic particles that are dispersed in the overlay coating, the ceramic particles being present in an amount and size sufficient to be stable and unreactive at temperatures up to about 1300° C. and to increase the strength of the overlay coating by a dispersion strengthening mechanism.  
     
     
         2 . A process according to  claim 1 , further comprising the step of depositing a thermal-insulating ceramic layer on the overlay coating.  
     
     
         3 . A process according to  claim 1 , wherein the overlay coating further contains chromium.  
     
     
         4 . A process according to  claim 1 , wherein the overlay coating consists of nickel, aluminum, chromium, the at least one reactive element, and the ceramic particles.  
     
     
         5 . A process according to  claim 1 , wherein the at least one reactive element is selected from the group consisting of zirconium, hafnium and yttrium.  
     
     
         6 . A process according to  claim 1 , wherein the ceramic particles comprise at least one compound selected from the group consisting of oxides, nitrides, and carbides of the at least one reactive element.  
     
     
         7 . A process according to  claim 6 , wherein the at least one reactive element is selected from the group consisting of zirconium, hafnium and yttrium.  
     
     
         8 . A process according to  claim 1 , wherein the overlay coating further contains at least one of tantalum and silicon.  
     
     
         9 . A process according to  claim 8 , wherein the ceramic particles comprise at least one compound selected from the group consisting of oxides, nitrides, and carbides of tantalum and silicon.  
     
     
         10 . A process according to  claim 1 , wherein at least some of the ceramic particles are formed by reacting the at least one reactive element with a gaseous species chosen from the group consisting of CH 4 , CO, CO 2 , N 2 , and O 2 .  
     
     
         11 . A process according to  claim 1 , wherein the ceramic particles are present in an amount of about 0.5 to about 5.0 volume percent of the overlay coating.  
     
     
         12 . A process according to  claim 1 , wherein the size of the ceramic particles is in a range of about 1 to about 2000 nanometers.  
     
     
         13 . A process of depositing a coating system on a nickel-base superalloy substrate of a gas turbine engine component, the coating system comprising a ceramic layer on a beta-phase NiAlCr intermetallic overlay bond coat, the overlay bond coat containing nickel, aluminum, chromium and zirconium, the process comprising the steps of: 
 depositing the overlay coating by a physical vapor deposition or thermal spray deposition so that some of the chromium and zirconium content of the coating is reacted to form ceramic particles that are dispersed in the overlay coating, the ceramic particles being at least one compound selected from the group consisting of oxides, nitrides, and carbides of chromium and zirconium, the ceramic particles being present in the overlay bond coat in an amount and size sufficient to be stable and unreactive at temperatures up to about 1300° C. and to increase the strength of the overlay bond coat by a dispersion strengthening mechanism; and then    depositing the ceramic layer on the overlay coating.    
     
     
         14 . A process according to  claim 13 , wherein at least some of the ceramic particles are formed by reacting chromium and zirconium with a gaseous species chosen from the group consisting of CH 4 , CO, CO 2 , N 2 , and O 2 .  
     
     
         15 . A process according to  claim 13 , wherein the ceramic particles are present in an amount of 0.5 to less than 5.0 volume percent of the overlay coating.  
     
     
         16 . A process according to  claim 13 , wherein the size of the ceramic particles is in a range of about 10 to about 1000 nanometers.  
     
     
         17 . A process according to  claim 13 , wherein the chromium content of the overlay bond coat is about 2 to about 15 atomic percent, and some of the chromium content is in the ceramic particles.  
     
     
         18 . A process according to  claim 13 , wherein the zirconium content of the overlay bond coat is about 0.05 to about 0.8 atomic percent, and some of the zirconium content is in the ceramic particles.