Method to produce gamma titanium aluminide articles having improved properties

Abstract

Methods are presented to produce duplex (DP) microstructures, nearly lamellar (NL) microstructures, and fully TMT lamellar (TMTL) microstructures in gamma titanium aluminide alloy articles. The key step for obtaining a specific type of microstructure is the post-hot work annealing treatment at a temperature in a specific range for the desired microstructure. The annealing temperatures range from Te+100° C. to Talpha-25° C. for duplex (DP) microstructures, from Talpha-25° C. to Talpha-5° C. for nearly lamellar (NL) microstructures, and from Talpha to Talpha+60° C. for fully TMT lamellar (TMTL) microstructures, where Te is the titanium-aluminum eutectoid temperature of the alloy and Talpha is the alpha transus temperature of the alloy. The times required for producing specific microstructures range from 2 min to 15 hours depending on microstructural type, alloy composition, annealing temperature selected, material section size, and desired grain-size. The heating rate to the post-hot work annealing treatment is critical and must be fast enough to avoid compositional segregation (in the two-phase field) and uneven grain growth. Cooling schemes and rates after the annealing treatments are determined according to the microstructural features of interest, and their stability.

We claim:  
     
       1. A process for producing duplex microstructure in an article of gamma titanium aluminide alloy containing 0.05 to 1.0 atomic percent boron, which comprises the steps of: 
       (a) hot working the article;  
       (b) annealing the hot worked article at an annealing temperature in the range of T e +100° C. to T α −25° C. for about 10 minutes to 15 hours;  
       (c) cooling said article from said annealing temperature to a preselected temperature between said annealing temperature and about 700° C. at a first cooling rate of about 10° to 1000° C./min and then cooled at a second rate ranging from said first cooling rate to water quenching to room temperature, and  
       (d) aging the so cooled article at an aging temperature in the range of 700° to 1050° C. for about 1 to 150 hours.  
     
     
       2. The process of claim  1  wherein said alloy has the composition Ti-(45.0-49)Al-(0-3)X-(0-6)Y-(0.05-1.0)B wherein X is Cr, Mn, V or any combination thereof, and Y is Nb, Ta, W, Mo, Zr, Hf, or any combination thereof. 
     
     
       3. The process of claim  2  wherein said alloy has the composition Ti-(46-47.5)Al-(1-3)Cr-(2-4)Nb-(0-0.3)W-(0.1-0.5)B. 
     
     
       4. A process for producing duplex microstructure in an article of gamma titanium aluminide alloy containing 0.05 to 1.0 atomic percent boron, which comprises the steps of: 
       (a) hot working the article;  
       (b) annealing the hot worked article at an annealing temperature in the range of T e +100° C. to T α −25° C. for about 10 minutes to 15 hours;  
       (c) cooling said article from said annealing temperature to an aging temperature in the range of 700° to 1050° C. at a cooling rate of about 5° to 1000° C./min; and  
       (d) aging the so cooled article at said aging temperature for about 1 to 150 hours.  
     
     
       5. The process of claim  4  wherein said alloy has the composition Ti-(45.0-49)Al-(0-3)X-(0-6)Y-(0.05-1.0)B wherein X is Cr, Mn, V or any combination thereof, and Y is Nb, Ta, W, Mo, Zr, Hf, or any combination thereof. 
     
     
       6. The process of claim  5  wherein said alloy has the composition Ti-(46-47.5)Al-(1-3)Cr-(2-4)Nb-(0-0.3)W-(0.1-0.5)B. 
     
     
       7. A process for producing nearly-lamellar microstructure in an article of gamma titanium aluminide alloy containing 0.05 to 1.0 atomic percent boron, which comprises the steps of: 
       (a) hot working the article;  
       (b) annealing the hot worked article at an annealing temperature in the range of T α −1° C. to T α −25° C. for about 0.5 to 10 hours;  
       (c) cooling said article from said annealing temperature to a preselected temperature between said annealing temperature and about 700° C. at a first cooling rate of about 5° to 1000° C./min and then cooled at a second rate ranging from said first cooling rate to water quenching to room temperature; and  
       (d) aging the so cooled article at an aging temperature in the range of 700° to 1050° C. for about 1 to 150 hours.  
     
     
       8. The process of claim  7  wherein said alloy has the composition Ti-(45.0-49)Al-(0-3)X-(0-6)Y-(0.05-1.0)B wherein X is Cr, Mn, V or any combination thereof, and Y is Nb, Ta, W, Mo, Zr, Hf, or any combination thereof. 
     
     
       9. The process of claim  8  wherein said alloy has the composition Ti-(46-47.5)Al-(1-3)Cr-(2-4)Nb-(0-0.3)W-(0.1-0.5)B. 
     
     
       10. A process for producing nearly-lamellar microstructure in an article of gamma titanium aluminide alloy containing 0.05 to 1.0 atomic percent boron, which comprises the steps of: 
       (a) hot working the article;  
       (b) annealing the hot worked article at an annealing temperature in the range of T α −1° C. to T α −25° C. for about 0.5 to 10 hours;  
       (c) cooling said article from said annealing temperature to an aging temperature in the range of 700° to 1050° C. at a cooling rate of about 5° to 1000° C./min; and  
       (d) aging the so cooled article at said aging temperature for about 1 to 150 hours.  
     
     
       11. The process of claim  10  wherein said alloy has the composition Ti-(45.0-49)Al-(0-3)X-(0-6)Y-(0.05-1.0)B wherein X is Cr, Mn, V or any combination thereof, and Y is Nb, Ta, W, Mo, Zr, Hf, or any combination thereof. 
     
     
       12. The process of claim  11  wherein said alloy has the composition Ti-(46-47.5)Al-(1-3)Cr-(2-4)Nb-(0-0.3)W-(0.1-0.5)B. 
     
     
       13. A process for producing fully TMT lamellar microstructure in an article of gamma titanium aluminide alloy containing 0.05 to 1.0 atomic percent boron, which comprises the steps of: 
       (a) hot working the article;  
       (b) pre-annealing the hot worked article at a temperature in the range of T α −1 2   C. to T α −100° C. for about 1 minute to 2 hours;  
       (c) heating the pre-annealed article to annealing temperature at a rate greater then 20° C./min;  
       (d) annealing the hot worked article at an annealing temperature in the range of T α  to T α +60° C. for about 1 minute to 10 hours;  
       (e) cooling said article from said annealing temperature to a preselected temperature between said annealing temperature and about 700° C. at a first cooling rate of about 5° to 1000° C./min and then cooled at a second rate ranging from said first cooling rate to water quenching to room temperature; and  
       (f) aging the cooled article at an aging temperature in the range of 700° to 1050° C. for about 1 to 150 hours.  
     
     
       14. The process of claim  13  wherein said alloy has the composition Ti-(45.0-49)Al-(0-3)X-(0-6)Y-(0.05-1.0)B wherein X is Cr, Mn, V or any combination thereof, and Y is Nb, Ta, W, Mo, Zr, Hf, or any combination thereof. 
     
     
       15. The process of claim  14  wherein said alloy has the composition Ti-(46-47.5)Al-(1-3)Cr-(2-4)Nb-(0-0.3)W-(0.1-0.5)B. 
     
     
       16. A process for producing fully TMT lamellar microstructure in an article of gamma titanium aluminide alloy containing 0.05 to 1.0 atomic percent boron, which comprises the steps of: 
       (a) hot working the article;  
       (b) pre-annealing the hot worked article at a temperature in the range of T α −1° C. to T α −100° C. for about 1 minute to 2 hours;  
       (c) heating the pre-annealed article to annealing temperature at a rate greater than 20° C./min;  
       (d) annealing the hot worked article at an annealing temperature in the range of T α  to T α +60° C. for about 1 minute to 10 hours;  
       (e) cooling said article from said annealing temperature to an aging temperature in the range of 700° to 1050° C. at a cooling rate of about 5° to 1000° C./min; and  
       (f) aging the cooled article at said aging temperature for about 1 to 150 hours.  
     
     
       17. The process of claim  16  wherein said alloy has the composition Ti-(45.0-49)Al-(0-3)X-(0-6)Y-(0.05-1.0)B wherein X is Cr, Mn, V or any combination thereof, and Y is Nb, Ta, W, Mo, Zr, Hf, or any combination thereof. 
     
     
       18. The process of claim  17  wherein said alloy has the composition Ti-(46-47.5)Al-(1-3)Cr-(2-4)Nb-(0-0.3)W-(0.1-0.5)B. 
     
     
       19. A process for producing fully lamellar microstructure in an article of gamma titanium aluminide alloy containing 0.05 to 1.0 atomic percent boron, which comprises the steps of: 
       (a) hot working the article;  
       (b) heating the said article to annealing temperature at a rate greater than 20° C./min;  
       (c) annealing the hot worked article at an annealing temperature in the range of T α  to T α +60° C. for about 1 minute to 10 hours;  
       (d) cooling said article from said annealing temperature to a preselected temperature between said annealing temperature and about 700° C. at a first cooling rate of about 5° to 1000° C./min and then cooled at a second rate ranging from said first cooling rate to water quenching to room temperature; and  
       (e) aging the cooled article at an aging temperature in the range of 700° to 1050° C. for about 1 to 150 hours.  
     
     
       20. The process of claim  19  wherein said alloy has the composition Ti-(45.0-49)Al-(0-3)X-(0-6)Y-(0.05-1.0)B wherein X is Cr, Mn, V or any combination thereof, and Y is Nb, Ta, W, Mo, Zr, Hf, or any combination thereof. 
     
     
       21. The process of claim  20  wherein said alloy has the composition Ti-(46-47.5)Al-(1-3)Cr-(2-4)Nb-(0-0.3)W-(0.1-0.5)B. 
     
     
       22. A process for producing fully lamellar microstructure in an article of gamma titanium aluminide alloy containing 0.05 to 1.0 atomic percent boron, which comprises the steps of: 
       (a) hot working the article;  
       (b) heating the said article to annealing temperature at a rate greater than 20° C./min;  
       (c) annealing the hot worked article at an annealing temperature in the range of T α  to T α +60° C. for about 1 minute to 10 hours;  
       (d) cooling said article from said annealing temperature to an aging temperature in the range of 700° to 1050° C. at a cooling rate of about 5° to 1000° C./min; and  
       (e) aging the cooled article at said aging temperature for about 1 to 150 hours.  
     
     
       23. The process of claim  22  wherein said alloy has the composition Ti-(45.0-49)Al-(0-3)X-(0-6)Y-(0.05-1.0)B wherein X is Cr, Mn, V or any combination thereof, and Y is Nb, Ta, W, Mo, Zr, Hf, or any combination thereof. 
     
     
       24. The process of claim  23  wherein said alloy has the composition Ti-(46-47.5)Al-(1-3)Cr-(2-4)Nb-(0-0.3)W-(0.1-0.5)B.