Rhodium-containing superalloy coatings and methods of making same

Claim 2

Method of forming a diffusion coating on a nickel base or cobalt base alloy structure which includes applying onto the structure surface to be coated an adherent layer of rhodium having a depth equal to between 5 percent and 35 percent of the intended depth of the diffusion coated base, prediffusing said rhodium layer into the structure surface under a nonoxidizing nonreactive atmosphere at a temperature between about 1400°F. and 2350°F., and thereafter diffusing aluminum into the prediffused rhodium containing structure surface at an elevated temperature and for a time sufficient to form with the rhodium and base metal said diffusion coating, whereby as a result of said prediffusing said alloy structure has a diffusion coating the inner boundary portion of which is relatively rich in rhodium.

Claim 3

Method according to claim 1 including diffusing said aluminum into said alloy structure surface from a diffusion coating pack containing aluminum, said surface being immersed in said pack.

Claim 4

Method according to claim 1 including diffusing said aluminum into said alloy structure from a coating thereof deposited onto said rhodium layer.

Claim 5

Method according to claim 1 in which said rhodium is vapor deposited onto said structure surface.

Claim 6

Method according to claim 1 in which said rhodium is deposited onto said structure surface from a bath containing the metal in which said surface is immersed.

Claim 7

Method according to claim 1 in which rhodium metal is applied onto the structure surface by plating, and said plate has a thickness not less than 10% of the intended depth of the diffusion coated case.

Claim 8

Method of forming a diffusion coating according to claim 1 wherein said adherent layer of rhodium is applied to have a depth equal to between 5% and 20% of the intended depth of the diffusion coated case.

Claim 9

Method according to claim 7 wherein said rhodium layer is prediffused into the structure surface for at least about 1 hour at a temperature between about 1900°F. and 2100°F.

Claim 10

Method according to claim 2 in which rhodium plating is effected by electroplating.

Claim 11

Method according to claim 1 in which said rhodium is diffused under vacuum.

Claim 12

Method according to claim 1 in which said rhodium is diffused under hydrogen.

Claim 13

Method according to claim 1 in which said rhodium is diffused under argon.

Claim 14

Cobalt or nickel base alloy structure having a diffusion coating, said coating consisting essentially of between 15 and 40 percent by weight aluminum, from 5 to 50 percent by weight rhodium, and the balance base metal, the inner boundary portion of said diffusion coating being between about 5 percent and 20 percent of the ultimate diffusion coating depth and relatively rich in rhodium to contain up to about 80 percent by weight rhodium, said diffusion coating being formed by prediffusing a rhodium coating having a thickness between 5 and 35 percent of said ultimate diffusion coating depth into the structure surface under a nonoxidizing nonreactive atmosphere at a temperature between about 1400°F. and 2350°F., and thereafter diffusing aluminum into the diffused-rhodium-containing structure surface.

Claim 15

Cobalt or nickel base alloy structure having a diffusion coating, said coating consisting essentially of between 15 and 40 percent by weight aluminum, from 5 to 50 percent by weight rhodium, and the balance base metal, the inner boundary portion of said diffusion coating being between about 5 percent and 20 percent of the ultimate diffusion coating depth and relatively rich in rhodium to contain up to about 80 percent by weight rhodium, said diffusion coating being formed by prediffusing a rhodium coating having a thickness between 5 and 35 percent of said ultimate diffusion coating depth into the structure surface under a nonoxidizing nonreactive atmosphere at a temperature between about 1400°F. and 2350°F., and thereafter diffusing aluminum into the diffused-rhodium-containing structure surface.

Claim 16

Alloy structure according to claim 13 in which said rhodium coating to be prediffused is at least 10% of the ultimate diffusion coating depth.

Claim 17

Alloy structure according to claim 14 wherein the inner boundary portion of said diffusion coating contains at least four times by weight as much rhodium as aluminum.

Claim 18

Alloy structure according to claim 14 in which the alloy is cobalt base.

Claim 19

Alloy structure according to claim 14 in which the alloy structure is nickel base.

Claim 20

Alloy structure according to claim 13 in which said coating contains from 10 to 30 percent by weight rhodium, 10 to 40 percent by weight aluminum and the balance base metal and metallic elements initially associated with the base metal in the alloy structure.

Claim 21

Alloy structure according to claim 13 wherein said rhodium coating which is diffused has a thickness of between 10 and 20 percent of the ultimate diffusion coating depth.