United States of America As Represented by the Secretary of the Air Force

Young-Won Kim

Dennis M Dimiduk

Francis H Froes

Yashwant R Mahajan

D Simon Shong

Frederick C Yolton

Paul A McQuay

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 T &plus;100&deg; C. to T&agr;&minus;25&deg; C. for duplex (DP) microstructures, from T&agr;&minus;25&deg; C. to T&agr;&minus;5&deg; C. for nearly lamellar (NL) microstructures, and from T&agr; to T&agr;&plus;60&deg; C. for fully TMT lamellar (TMTL) microstructures, where T is the titanium-aluminum eutectoid temperature of the alloy and T&agr; 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.

Method to produce gamma titanium aluminide articles having improved properties

Gamma titanium aluminide alloys having the composition Ti-(45.5-47.5)Al-(0-3.0)X-(1-5)Y-(0.05-1.0)W, where X is Cr, Mn or any combination thereof, and Y is Nb, Ta or any combination thereof (at %), are treated to provide specific microstructures. To obtain duplex microstructures, the annealing temperature (T.sub.a) range is the eutectoid temperature (T.sub.e)+100.degree. C. to the alpha transus temperature (T.sub..alpha.)-30.degree. C.; to obtain nearly lamellar microstructures, the annealing temperature range is T.sub..alpha. -20.degree. C. to T.sub..alpha. -1.degree. C.; to obtain fully lamellar microstructures, the annealing temperature range is T.sub..alpha. to T.sub..alpha. +50.degree. C. The times required for producing these microstructures range from 0.25 to 15 hours, depending on the desired microstructure, alloy composition, annealing temperature selected, material section size and grain size desired. The cooling schemes and rates after annealing depend mainly on the microstructure type and stability; for duplex and nearly lamellar microstructures, the initial cooling rate is 5.degree. to 1000.degree. C./min, while for fully lamellar microstructure, the the initial cooling rate is 5.degree. to 100.degree. C./min. The article can be cooled at the initial rate directly to the aging temperature; alternatively, the article can be cooled at the initial rate down to a temperature between room temperature and the annealing temperature, then cooled to room temperature at a cooling rate between the initial rate and water quenching, after which the article is aged. Following annealing, the article is aged at a temperature in the range of 700.degree. C. to 1050.degree. C. for about 4 to 150 hours.

Method to produce gamma titanium aluminide articles having improved

Gamma titanium aluminide alloys having the composition Ti--(45.5-47.5)Al--(0-3.0)X--(1-5)Y--(0.05-1.0)W, where X is Cr, Mn or any combination thereof, and Y is Nb, Ta or any combination thereof (at %), are treated to provide specific microstructures. To obtain duplex microstructures, the annealing temperature (T.sub.a) range is the eutectoid temperature (T.sub.e)+100.degree. C. to the alpha transus temperature (T.sub..alpha.)-30.degree. C.; to obtain nearly lamellar microstructures, the annealing temperature range is T.sub..alpha. -20.degree. C. to T.sub..alpha. -1.degree. C.; to obtain fully lamellar microstructures, the annealing temperature range is T.sub..alpha. to T.sub..alpha. +50.degree. C. The times required for producing these microstructures range from 0.25 to 15 hours, depending on the desired microstructure, alloy composition, annealing temperature selected, material section size and grain size desired. The cooling schemes and rates after annealing depend mainly on the microstructure type and stability; for duplex and nearly lamellar microstructures, the initial cooling rate is 5.degree. to 1000.degree. C./min, while for fully lamellar microstructure, the initial cooling rate is 5.degree. to 100.degree. C./min. The article can be cooled at the initial rate directly to the aging temperature; alternatively, the article can be cooled at the initial rate down to a temperature between room temperature and the annealing temperature, then cooled to room temperature at a cooling rate between the initial rate and water quenching, after which the article is aged. Following annealing, the article is aged at a temperature in the range of 700.degree. C. to 1050.degree. C. for about 4 to 150 hours.

Gamma titanium aluminide alloy articles having improved properties are produced by the following methods: The first of these methods comprises the steps of: (a) heat treating an alloy billet or preform at a temperature in the approximate range of T.sub..alpha. to T.sub..alpha. +100.degree. C. for about 0.5 to 8 hours, (b) shaping the billet at a temperature between T.sub..alpha. -30.degree. C. and T.sub..alpha. to produce a shaped article, and (c) aging the thus-shaped article at a temperature between about 750.degree. and 1050.degree. C. for about 2 to 24 hours. The second method comprises (a) rapidly preheating an alloy preform to a temperature in the approximate range of T.sub..alpha. to T.sub..alpha. +100.degree. C., (b) shaping the billet at a temperature between T.sub..alpha. and T.sub..alpha. +100.degree. C. to produce a shaped article, and (c) aging the thus-shaped article at a temperature between about 750.degree. and 1050.degree. C. for about 2 to 24 hours. The preform is held at the preheat temperature for 0.1 to 2 hours, just long enough to bring the preform uniformly to the shaping temperature. The third method comprises the steps of: (a) heat treating an alloy billet or preform at a temperature in the approximate range of T.sub..alpha. to T.sub..alpha. +100.degree. C. for about 0.5 to 8 hours, (b) rapidly heating the preform to shaping temperature, if the shaping temperature is greater than the heat treatment temperature, (c) shaping the preform at a temperature between T.sub..alpha. and T.sub..alpha. +100.degree. C. to produce a shaped article, and (d) aging the thus-shaped article at a temperature between about 750.degree. and 1050.degree. C. for about 2 to 24 hours. The fourth method comprises the steps of: (a) heat treating an alloy billet or preform at a temperature in the approximate range of T.sub..alpha. -40.degree. C. to T.sub..alpha. to for about 0.1 to 2 hours, (b) rapidly preheating the preform to shaping temperature, (c) shaping the preform at a temperature between T.sub..alpha. and T.sub..alpha. +100.degree. C. to produce an shaped article, and (d) aging the thus-shaped article at a temperature between about 750.degree. and 1050.degree. C. for about 2 to 24 hours.

A first method for producing articles of gamma titanium alumide alloy having improved properties comprises the steps of: (a) shaping the article at a temperature between the titanium-aluminum eutectoid temperature of the alloy and the alpha-transus temperature of the alloy, and (b) aging the thus-shaped article at a temperature between about 750.degree. and 1050.degree. C. for about 4 to 150 hours. Shaping is preferably carried out at a temperature about 0.degree. to 50.degree. C. below the alpha-transus temperature. A second method for producing articles of gamma titanium aluminide alloy having improved properties comprises the steps of: (a) shaping the article at a temperature in the approximate range of about 130.degree. C. below the titanium-aluminum eutectoid temperature of the alloy to about 20.degree. C. below the alpha-transus temperature of the alloy; (b) heat treating the thus-shaped article at about the alpha-transus temperature of the alloy for about 15 to 120 minutes; and (c) aging the thus-heat treated article at a temperature between about 750.degree. and 1050.degree. C. for about 4 to 300 hours.

A method for refining the microstructure and enhancing the processability of titanium aluminum alloys containing about 45 to 55 atomic percent aluminum which comprises the steps of:

Low temperature hydrogenation of gamma titanium aluminide

An improved alloy consisting essentially of about 6 to 10 weight percent Fe, about 2 to 10 weight percent Gd, balance Al. The alloy may also contain minor amounts of one or more refractory metals.

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Dayton, OH, United States of America

Young-Won Kim