Turbocharger turbine wheels having an alpha-alumina coating and methods for manufacturing the same

1. An alpha-alumina coated turbocharger turbine wheel comprising:

a hub portion;

a plurality of blades disposed about the hub portion, each blade of the plurality of blades having a leading edge and a trailing edge;

a centerline passing axially through the hub portion; and

a back-side wall defined radially between the leading edge of each blade of the plurality of blades and the centerline,

wherein the turbocharger turbine wheel is comprised of a metal alloy and a surface coating layer of alpha-alumina, the surface coating layer of alpha-alumina being disposed

only on the hub portion, the plurality of blades, and a radially-outer portion of the back-side wall, the radially-outer portion being defined between a radial distance from the centerline and the leading edge of each blade of the plurality of blades.

2. The turbocharger turbine wheel of claim 1 , wherein the metal alloy is a nickel-based superalloy.

3. The turbocharger turbine wheel of claim 1 , wherein the metal alloy is a titanium-aluminum alloy.

4. The turbocharger turbine wheel of claim 1 , wherein a surface of the back-side wall from the centerline extending radially outward to the radial distance comprises the metal alloy.

5. The turbocharger turbine wheel of claim 1 , wherein the surface coating layer of alpha-alumina has a substantially uniform thickness.

6. The turbocharger turbine wheel of claim 5 , wherein the substantially uniform thickness is selected from a value within the range of about 5 microns to about 20 microns.

7. The turbocharger turbine wheel of claim 6 , wherein the substantially uniform thickness is selected from a value within the range of about 8 microns to about 15 microns.

8. The turbocharger turbine wheel of claim 7 , wherein the substantially uniform thickness is about 10 microns.

9. A method for manufacturing an alpha-alumina coated turbocharger turbine wheel, the method comprising:

manufacturing or obtaining an un-coated turbocharger turbine wheel, the un-coated turbocharger turbine wheel comprising a hub portion, a plurality of blades disposed about the hub portion, each blade of the plurality of blades having a leading edge and a trailing edge, a centerline passing axially through the hub portion, and a back-side wall defined radially between the leading edge of each blade of the plurality of blades and the centerline, wherein the un-coated turbocharger turbine wheel is made of a metal alloy;

masking a portion of the back-side wall of the un-coated turbocharger turbine wheel using a physical vapor deposition-compatible masking material, wherein the portion of the back-side wall is annular and is defined as an area extending radially-outward form the centerline to a radial distance that is radially-inward from the leading edge of each blade of the plurality of blades; and

subjecting the masked, un-coated turbocharger turbine wheel to an alpha-alumina physical vapor deposition process, thereby coating a layer of alpha-alumina on non-masked portions of the masked, un-coated turbocharger turbine wheel.

10. The method of claim 9 , wherein the physical vapor deposition-compatible masking material comprises a temperature-resistant polymeric and/or metallic material.

11. The method of claim 9 , further comprising performing reactive ion etching on the masked, un-coated turbocharger turbine wheel prior to subjecting the masked, un-coated turbocharger turbine wheel to the alpha-alumina physical vapor deposition process.

12. The method of claim 9 , wherein the alpha-alumina physical vapor deposition process is performed at a temperature of about 400° C. to about 500° C.

13. The method of claim 9 , wherein the metal alloy comprises a nickel-based superalloy or a titanium-aluminum alloy.

14. The method of claim 9 , further comprising performing one or more post-deposition processes on the alpha-alumina coated turbocharger turbine wheel.

15. The method of claim 14 , wherein the one or more post-deposition processes comprises removing the physical vapor deposition-compatible masking material from the alpha-alumina coated turbocharger turbine wheel.

16. The method of claim 14 , wherein the one or more post-deposition processes comprises machining the alpha-alumina coated turbocharger turbine wheel to final tolerances.

17. The method of claim 14 , wherein the one or more post-deposition processes comprises rotationally balancing the alpha-alumina coated turbocharger turbine wheel.

18. The method of claim 9 , wherein subjecting the masked, un-coated turbocharger turbine wheel to an alpha-alumina physical vapor deposition process is performed for a period of time sufficient to deposit a layer of alpha-alumina to a thickness from about 5 microns to about 20 microns.

19. The method of claim 18 , wherein subjecting the masked, un-coated turbocharger turbine wheel to an alpha-alumina physical vapor deposition process is performed for a period of time sufficient to deposit a layer of alpha-alumina to a thickness from about 8 microns to about 15 microns.

20. The method of claim 19 , wherein subjecting the masked, un-coated turbocharger turbine wheel to an alpha-alumina physical vapor deposition process is performed for a period of time sufficient to deposit a layer of alpha-alumina to a thickness of about 10 microns.