Ion beam assisted deposition of thermal barrier coatings

1. A process for coating a metallic substrate with alpha-phase alumina, comprising steps of:

a) preheating a metallic substrate to at least 500° C. in a vacuum chamber by using a heated thermal cage surrounding the substrate;

b) exposing the pre-heated substrate to a plume of alumina evaporated from an alumina ingot heated with an electron beam;

c) depositing alumina from the plume on to the substrate while simultaneously irradiating the deposit with a collimated beam of energetic ions; thereby transforming the deposited alumina into alpha-phase alumina; and

d) stopping the process when a desired thickness of the alpha-phase alumina has been reached, thus forming an alpha-phase alumina coating;

wherein the thickness of the alpha-phase alumina coating is between 0.1 and 2.0 microns;

wherein the substrate temperature does not exceed 800 during the coating process;

wherein the collimated beam of energetic ions comprises argon ions with an energy between 200 and 600 eV;

wherein the process does not require performing a post-coating anneal at a temperature of at least 1100 for 2 or more hours in order to transform the deposited alumina into alpha-phase alumina;

wherein the process does not comprise exposing the substrate to a plasma glow discharge during the depositing of the alumina; and

further comprising using the collimated beam of energetic ions to sputter-clean the substrate prior to depositing the alumina.

2. A process for coating a metallic substrate with a thermal barrier coating, comprising steps of:

a) providing a metallic substrate;

b) pumping down a vacuum chamber to a pressure lower than atmospheric pressure; preheating the substrate to at least 500° C. in the vacuum chamber by using a heated thermal cage surrounding the substrate; and feeding oxygen gas into the vacuum chamber; then in the vacuum chamber

c) exposing the preheated substrate to a plume of yttria-stabilized zirconia (YSZ) evaporated from a YSZ ingot heated with an electron beam; and

d) depositing the YSZ from the plume onto the substrate while irradiating the deposit with a collimated beam of energetic ions; and

e) stopping the process when a desired thickness of the YSZ has been reached, thus forming the thermal barrier coating;

wherein the substrate temperature does not exceed 800° C. during the coating process;

wherein the collimated beam of energetic ions comprises argon ions with an energy between 200 and 600 eV;

wherein the ion beam cycles on and off during the YSZ depositing with a 50/50 balanced duty cycle, wherein the length of the ON time and OFF time ranges from between 20 and 120 seconds;

wherein the angle of incidence with which the ion beam strikes the substrate varies periodically during the YSZ depositing from a minimum of zero degrees (perpendicular incidence) to a maximum of 90 degrees (grazing incidence); and

wherein the substrate pivots back and forth +/−30 degrees during the depositing, with a hold period at each of the two pivot angles ranging from 10 to 90 seconds.

3. The process of claim 2 , wherein the thickness of the YSZ coating is 30-300 microns.

4. The process of claim 2 , wherein the background partial pressure of oxygen is less than 100 mPa during the YSZ depositing.

5. The process of claim 2 , wherein the process does not comprise exposing the substrate to a plasma glow discharge during the YSZ depositing.

6. The process of claim 2 , further comprising using the collimated beam of energetic ions to sputter-clean the substrate prior to depositing the YSZ.

7. The process of claim 2 , wherein a molecular flux ratio of argon-ion flux to ZrO-molecule flux to the substrate is greater than or equal to 0.1 while depositing the YSZ.

8. The process of claim 2 , wherein a sufficient rate of the oxygen gas is fed into the vacuum chamber so that the YSZ formed on the substrate is fully stoichiometric YSZ.

9. A process for coating metallic substrate with a thermal barrier coating, comprising steps of:

a) providing a metallic substrate pre-coated with a bondcoat layer;

b) pumping down a vacuum chamber to a pressure lower than atmospheric pressure; preheating the substrate to at least 500° C. in the vacuum chamber by using a heated thermal cage surrounding the substrate; and feeding oxygen gas into the vacuum chamber; then in the vacuum chamber

c) depositing an adhesion layer onto the bondcoat; comprising:

1) exposing the bondcoat to a plume of alumina evaporated from an alumina ingot heated with an electron beam; and

2) depositing alumina from the plume onto the bondcoat while simultaneously irradiating the deposit with a collimated beam of energetic ions; thereby transforming the deposited alumina into alpha-phase alumina; then

d) depositing a thermal barrier material onto the adhesion layer; comprising:

1) exposing the adhesion layer to a plume of yttria-stabilized zirconia (YSZ) evaporated from a YSZ ingot heated with the electron beam; and

2) depositing the YSZ from the plume onto the adhesion layer while irradiating the adhesion layer with the collimated beam of energetic ions; and then

e) stopping the process when a desired thickness of the thermal barrier material has been reached, thus forming the thermal barrier coating;

wherein the thickness of the alpha-phase alumina coating is between 0.1 and 2.0 microns;

wherein the substrate temperature does not exceed 800° C. during the coating process;

wherein the collimated beam of energetic ions comprises argon ions with an energy between 200 and 600 eV;

wherein the process does not require performing a post-coating anneal at a temperature of at least 1100 for 2 or more hours in order to transform the deposited alumina into alpha-phase alumina;

wherein the ion beam cycles on and off during the YSZ depositing with a 50/50 balanced duty cycle, wherein the length of the ON time and OFF time ranges from between 20 and 120 seconds;

wherein the angle of incidence with which the ion beam strikes the substrate varies periodically during the YSZ depositing from a minimum of zero degrees (perpendicular incidence) to a maximum of 90 degrees (grazing incidence); and

wherein the substrate pivots back and forth +/−30 degrees during the depositing, with a hold period at each of the two pivot angles ranging from 10 to 90 seconds; and

further comprising using the collimated beam of energetic ions to sputter-clean the substrate prior to depositing the alumina.

10. The process of claim 9 , wherein the bondcoat comprises Ni 2 Al 3 .

11. The process of claim 9 , wherein the process does not comprise exposing the substrate to a plasma glow discharge during the alumina depositing.

12. The process of claim 9 , wherein the thickness of the YSZ coating is 30-300 microns.

13. The process of claim 9 , wherein the background partial pressure of oxygen is less than 100 mPa during the YSZ depositing.

14. The process of claim 9 , wherein the step a) through e) are completed within a single pump-down cycle of the vacuum chamber.

15. The process of claim 9 , wherein a sufficient rate of the oxygen gas is fed into the vacuum chamber so that the YSZ formed on the substrate is fully stoichiometric YSZ.

16. A process for coating a metallic substrate with a thermal barrier coating, comprising steps of:

a) providing a metallic substrate pre-coated with a bondcoat layer;

b) pumping down a vacuum chamber to a pressure lower than atmospheric pressure; preheating the substrate to at least 500° C. in the vacuum chamber by using a heated thermal cage surrounding the substrate; and feeding oxygen gas into the vacuum chamber; then in the vacuum chamber

c) depositing an adhesion layer onto the bondcoat; comprising:

1) exposing the bondcoat to a plume of alumina evaporated from an alumina ingot heated with an electron beam; and

2) depositing alumina from the plume onto the bondcoat while simultaneously irradiating the deposit with a collimated beam of energetic ions; thereby transforming the deposited alumina into alpha-phase alumina; then

d) depositing a graded transition layer onto the adhesion layer; comprising:

1) exposing the adhesion layer to both an alumina plume from an alumina ingot heated with an electron beam and simultaneously to a yttria-stabilized zirconia (YSZ) plume from a YSZ ingot heated with the same, or different, electron beam; and

2) depositing a mixture of alumina and YSZ onto the adhesion layer while irradiating the deposit with the collimated beam of energetic ions;

wherein—the graded transition layer varies continuously in a substantially linear fashion from being mostly pure alumina near the bottom of the graded layer, to being mostly pure YSZ near the top of the graded layer, produced by gradually decreasing the temperature of the alumina ingot while gradually increasing the temperature of the YSZ ingot as the graded layer grows thicker; and then

e) depositing a thermal barrier material onto the graded transition layer; comprising:

1) exposing the graded transition layer to the plume of YSZ evaporated from the heated YSZ ingot; and

2) depositing the YSZ from the plume onto the graded transition layer while irradiating the deposit with a collimated beam of energetic ions; and

f) stopping the process when a desired thickness of the thermal barrier material has been reached, thus forming a thermal barrier coating;

wherein the thickness of the alpha-phase alumina coating is between 0.1 and 2.0 microns;

wherein the substrate temperature does not exceed 800 during the coating process;

wherein the collimated beam of energetic ions comprises argon ions with an energy between 200 and 600 eV;

wherein the process does not require performing a post-coating anneal at a temperature of at least 1100° C. for 2 or more hours in order to transform the deposited alumina into alpha-phase alumina;

wherein the ion beam cycles on and off during the YSZ depositing with a 50/50 balanced duty cycle, wherein the length of the ON time and OFF time ranges from between 20 and 120 seconds;

wherein the angle of incidence with which the ion beam strikes the substrate varies periodically during the YSZ depositing from a minimum of zero degrees (perpendicular incidence) to a maximum of 90 degrees (grazing incidence); and

wherein the substrate pivots back and forth +/−30 degrees during the depositing, with a hold period at each of the two pivot angles ranging from 10 to 90 seconds; and

further comprising using the collimated beam of energetic ions to sputter-clean the substrate prior to depositing the alumina.

17. The process of claim 16 , wherein a single electron beam is used to heat both the alumina ingot and the YSZ ingot; and further comprising timesharing the single electron beam between the alumina ingot and the YSZ ingot while depositing the graded transition layer.

18. The process of claim 16 , wherein the steps a) through f) are completed within a single pump-down cycle of the vacuum chamber.

19. The process of claim 16 , wherein a sufficient rate of the oxygen gas is fed into the vacuum chamber so that the YSZ formed on the substrate is fully stoichiometric YSZ.