Overlay coatings for superalloys

Abstract

Improved coating compositions are described for the protection of superalloys at elevated temperatures. The coatings are of the MCrAlY type where M is nickel or cobalt and are significantly improved by the addition of from 0.1-7% silicon and 0.1-2% hafnium. Coatings of the invention are preferably applied by plasma spraying and as so applied are found to be substantially more effective than prior art coatings.

We claim: 
     
       1. A gas turbine engine component which comprises a substrate selected from the group consisting of Ni and Co base superalloys having thereon a protective coating consisting essentially of 5-40% Cr, 8-35% Al, 0.1-2.0% Y, .[.1-7.0%.]. .Iadd.0.1-7% .Iaddend.Si and 0.1-2.0% Hf balance selected from the group consisting of Ni, Co and mixtures thereof. 
     
     
       2. A coated article as in claim 1 in which the superalloy substrate is a nickel base superalloy and in which the coating contains 15-25% Cr, 10-20% Al, up to 30% Co, balance essentially Ni. 
     
     
       3. A coated article as in claim 2 in which the coating contains 15-25% Co. 
     
     
       4. A coated article as in claim 1 in which the superalloy substrate is a cobalt base superalloy and in which the coating contains 15-35% Cr, 10-20% Al, up to 35% Ni, balance essentially Co. 
     
     
       5. A coated article as in claims 1, 2, 3, or 4, intended for use at temperatures in excess of about 2100° F., in which the Si content is limited to a maximum of 2%. 
     
     
       6. A coated article as in claims 1, 2, 3 or 4 in which the substrate is essentially free from hafnium and the coating contains at least 0.2% Hf.