Method of protecting the surfaces of metal parts against corrosion at high temperature, and a part treated by the method

Claim 1

A coated metal part comprising a metal substrate and a protective coating, wherein said metal substrate consists essentially of at least one metal selected from the group consisting of Ni, Co, and Fe, and said protective coating is free of blisters and consists essentially of a deposit and a predeposit provided between the substrate and the deposit, wherein said predeposit, which comprises at least one layer, comprises: (1) Pd; and (2) at least one barrier metal selected from the group consisting of Ni, Co, and Cr, wherein said barrier metal is provided on the substrate simultaneously with said Pd and/or said barrier metal forms at least one overlying layer covering the Pd provided on the substrate, and wherein said deposit comprises a Pd-modified aluminide of the metal which constitutes the metal substrate and is at least one member selected from the group consisting of Ni, Co, and Fe, said aluminide being formed by aluminization of the substrate coated with the predeposit in an atmosphere containing hydrogen, and said aluminide being modified by diffusion of Pd from said predeposit into the deposit.

Claim 12

A method of protecting the surface of a metal substrate, wherein the metal substrate consists essentially of at least one metal selected from the group consisting of Ni, Co, and Fe, said method comprising the steps of: (1) preparing a pretreated substrate by forming on the substrate a predeposit by deposition and/or diffusion of a material comprising Pd and at least one barrier metal selected from the group consisting of Ni, Co, and Cr, wherein said predeposit may be provided in a single stage or in successive stages, and the material added to the surface of the substrate during one of said successive stage may be different from the material added during the other successive stages, provided that for each stage in which Pd is added to the surface of the substrate, at least one barrier metal must be added simultaneously with said Pd and/or at least one barrier metal must be added subsequently to the stage in which Pd is added; and (2) forming on the predeposit a deposit by deposition and/or diffusion of aluminum under an atmosphere containing hydrogen, whereby is obtained a blister-free protective coating of Pd-modified aluminide of said metal which constitutes the metal substrate and is selected from the group consisting of Ni, Co, and Fe.

Claim 13

A method of protecting the surface of a metal substrate, wherein the metal substrate consists essentially of at least one metal selected from the group consisting of Ni, Co, and Fe, said method comprising the steps of: (1) preparing a pretreated substrate by forming on the substrate a predeposit by deposition and/or diffusion of a material comprising Pd and at least one barrier metal selected from the group consisting of Ni, Co, and Cr, wherein said predeposit may be provided in a single stage or in successive stages, and the material added to the surface of the substrate during one of said successive stage may be different from the material added during the other successive stages, provided that for each stage in which Pd is added to the surface of the substrate, at least one barrier metal must be added simultaneously with said Pd and/or at least one barrier metal must be added subsequently to the stage in which Pd is added; and (2) forming on the predeposit a deposit by deposition and/or diffusion of aluminum under an atmosphere containing hydrogen, whereby is obtained a blister-free protective coating of Pd-modified aluminide of said metal which constitutes the metal substrate and is selected from the group consisting of Ni, Co, and Fe.