Methods of applying chromium diffusion coatings onto selective regions of a component
Unique and improved chromizing processes are disclosed. The processes involve forming localized chromizing coatings onto selected regions of a substrate. The chromium diffusion coatings are locally applied to selected regions of substrates in a controlled manner, in comparison to conventional chromizing processes, and further in a manner that produces less material waste and does not require masking. A second coating can be selectively applied onto other regions of the substrate.
1. A method for producing a chromium diffusion coating onto selected regions of a substrate, comprising the steps of:
providing a chromium-containing slurry;
applying the chromium-containing slurry onto localized surfaces of the substrate;
curing the slurry;
heating the slurry in a protective atmosphere to a predetermined temperature for a predetermined duration;
generating chromium-containing vapors;
diffusing the chromium into said localized surfaces to form the coating, said coating having a microstructure characterized by a substantial reduction in nitride and oxide inclusions and reduced levels of α-Cr phase in comparison to conventional chromizing processes.
2. The method of claim 1 , wherein said method comprises locally applying a second coating onto the substrate.
3. The method of claim 2 , wherein said second coating comprises an aluminide coating.
4. The method of claim 2 , wherein said second coating comprises a MCrAlY coating.
5. The method of claim 1 , wherein the step of applying the slurry comprises brushing, spraying, dipping, dip-spinning, injection, or any combination thereof.
6. The method of claim 1 , wherein said localized surfaces are subject to corrosion attack.
7. A method for producing a localized chromium diffusion coating and a localized aluminide diffusion coating onto selected regions of a substrate simultaneously, comprising the steps of:
providing a chromium-containing slurry;
applying the chromium-containing slurry onto a first region of the substrate, characterized by an absence of masking;
providing an aluminide-containing material;
heating the chromium-containing slurry and the aluminide-containing material in a protective atmosphere to a predetermined temperature for a predetermined duration;
diffusing chromium into the first region;
diffusing aluminum into a second region in the absence of masking;
forming the localized chromium diffusion coating along the first region, said chromium diffusion coating having a microstructure characterized by a substantial reduction in nitride and oxide inclusions and reduced levels of α-Cr phase in comparison to conventional chromizing processes; and
forming a localized aluminide-diffusion coating along the second region.
8. The method of claim 7 , wherein said first region is subject to corrosion attack.
9. The method of claim 7 , wherein said second region is subject to oxidation attack.
10. The method of claim 7 , wherein the step of applying the chromium slurry comprises brushing, spraying, dipping, dip-spinning or injection or any combination thereof.
11. The method of claim 7 , wherein said chromium diffusion coating and aluminide diffusion coating are formed simultaneously during diffusion treatment.
12. The method of claim 7 , wherein the substrate is a gas turbine blade and said first region comprises a shank.
13. The method of claim 12 , wherein said second region comprises an airfoil.
14. A method for producing a localized chromium diffusion coating and a localized aluminide diffusion coating onto selected regions of a blade simultaneously, comprising the steps of:
providing a chromium-containing slurry;
applying the chromium-containing slurry onto a shank of the blade, characterized by an absence of masking;
providing aluminide-containing material within the retort;
loading the partially coated blade into the retort;
heating the partially coated blade;
generating aluminum containing vapors and chromium containing vapors;
diffusing chromium from the chromium-containing vapors into an external region of the shank of the blade;
diffusing aluminum from the aluminum-containing vapors into an airfoil of the blade;
forming the localized chromium diffusion coating along the shank, said chromium diffusion coating having a microstructure characterized by a substantial reduction in nitride and oxide inclusions and reduced levels of α-Cr phase in comparison to conventional chromizing processes; and
forming the localized aluminide-diffusion coating along the airfoil.
15. The method of claim 14 , wherein said chromium-containing slurry is locally applied onto the shank.
16. The method of claim 14 , wherein said localized diffusion coating forms in the absence of masking.