High integrity CoCrAl(Y) coated nickel-base superalloys

Abstract

A high temperature oxidation and corrosion resistant coated nickel-base superalloy article comprising (a) a nickel-base superalloy article, and .[.(b) a first.]. .Iadd.adjacent thereto (b) a .Iaddend.CoCrAl(Y) coating .Iadd.having a substantially uniform .Iaddend.composition .[.consisting essentially.]. .Iadd.composed .Iaddend.of, on a weight basis, approximately 26-32% chromium, 3-9% aluminum, 0-1% yttrium, the rare earth elements, platinum or rhodium, and the balance .[.nickel.]. .Iadd.cobalt and impurities ordinarily associated with the aforementioned constituents. .Iaddend.

I claim: 
     
       1. A high temperature oxidation and corrosion resistant coated nickel-base superalloy article .[.having a thermal expansion coefficient value in inches per inch per °F. measured over a temperature range of (i) 100°-1200° F. of from 8.45 to 9.05, and   (ii) 100°-1740° F. of from 9.45 to 10.05;.]. .Iadd.characterized by high coating-substrate interface integrity, said article .Iaddend.comprising:   (a) a nickel-base superalloy, and   (b) a .[.first.]. CoCrAl(Y) coating .Iadd.providing the outer surface of said article, said coating having a substantially uniform .Iaddend.composition .[.consisting essentially.]. .Iadd.composed .Iaddend.of, on a weight basis, approximately 26-32 percent chromium, 3-9 percent aluminum, and 0-1 percent yttrium, other rare earth elements, platinum or rhodium, and the balance cobalt .Iadd.and impurities ordinarily associated with the aforementioned constituents.Iaddend..[...]..Iadd., said nickel-base superalloy and said CoCrAl(Y) coating having substantially matching thermal expansion coefficient values with the maximum difference between the thermal expansion coefficient value of said substrate and the thermal expansion coefficient value of said coating being about 4 percent over a temperature range from 100° F. to 1740° F. .Iaddend.   
     
     
       2. A claim 1 article, wherein .[.(a) said nickel-base superalloy consists essentially of, on a weight basis,.].   ______________________________________                                    
Ingredient           IN-738                                               
______________________________________                                    
C                    0.17                                                 
Mn                   0.20                                                 
Si                   0.30                                                 
Cr                   16.0                                                 
Ni                   Bal.                                                 
Co                   8.5                                                  
Mo                   1.75                                                 
W                    2.6                                                  
Cb                   0.9                                                  
Ti                   3.4                                                  
Al                   3.4                                                  
B                    0.01                                                 
Zr                   0.10                                                 
Fe                   0.50                                                 
Other                1.75 Ta                                              
______________________________________                                    
       .[.(b) said first.]. .Iadd.the .Iaddend.coating contains 29% chromium, 6% aluminum, 1% yttrium and the balance cobalt. .[.3. A claim 2 article, further comprising   (c) an overcoating of aluminum..]. .[.4. A claim 3 article, wherein   (b) said first coating has a thickness of about 1-20 mils,   (c) said second coating penetrates the first coating to a depth no nearer than 1/2 mil measured from the interface of the nickel-base superalloy and first coating..]. .[.5. A claim 4 article, wherein   (b) said first coating is deposited by physical vapor deposition and the coating thickness is about 1-5 mils,   (c) said second coating is deposited by chemical vapor deposition..]. .[.6. The claim 4 article, wherein   (b) said first coating is deposited by plasma spraying and has a coating thickness of 3-10 mils..].