Methods for processing titanium aluminide intermetallic compositions

Abstract

Methods of processing compositions containing titanium and aluminum, especially titanium aluminide intermetallic compositions (TiAl intermetallics) based on the TiAl (gamma) intermetallic compound. The methods entail processing steps that include a hot isostatic pressing (HIP) cycle and a heat treatment cycle that can be performed in a single vessel. TiAl intermetallic compositions processed in this manner preferably exhibit a duplex microstructure containing equiaxed and lamellar morphologies.

1 . A method of processing a titanium aluminide intermetallic composition based on a TiAl intermetallic compound to yield a duplex microstructure containing equiaxed and lamellar morphologies of the gamma TiAl phase, the method comprising:
 hot isostatic pressing the titanium aluminide intermetallic composition at a temperature of at least 1260° C.;   cooling the titanium aluminide intermetallic composition to a temperature of not less than 1120° C.;   heat treating the titanium aluminide intermetallic composition at a temperature of about 1150 to about 1200° C.; and then   cooling the titanium aluminide intermetallic composition to room temperature;   wherein the titanium aluminide intermetallic composition exhibits the duplex microstructure following the step of cooling the titanium aluminide intermetallic composition to room temperature.   
     
     
         2 . The method according to  claim 1 , wherein the hot isostatic pressing step is conducted at a pressure of at least 1030 bar. 
     
     
         3 . The method according to  claim 1 , wherein the hot isostatic pressing step is conducted at a pressure of at least 1240 bar. 
     
     
         4 . The method according to  claim 1 , wherein the hot isostatic pressing step is conducted at a temperature of at least 1290° C. 
     
     
         5 . The method according to  claim 1 , wherein the hot isostatic pressing step is conducted at a temperature of about 1300 to about 1330° C. 
     
     
         6 . The method according to  claim 1 , wherein the hot isostatic pressing step is conducted for a duration of about 2.5 to about 5 hours. 
     
     
         7 . The method according to  claim 1 , wherein the titanium aluminide intermetallic composition is cooled to a temperature of not less than 1150° C. during the cooling step. 
     
     
         8 . The method according to  claim 1 , wherein the titanium aluminide intermetallic composition is cooled to a temperature of 1150 to about 1175° C. during the cooling step. 
     
     
         9 . The method according to  claim 1 , wherein the heat treatment step is performed at a temperature of about 1150 to about 1175° C. 
     
     
         10 . The method according to  claim 1 , wherein the heat treatment step is performed for a duration of about two to about six hours. 
     
     
         11 . The method according to  claim 1 , wherein the titanium aluminide intermetallic composition consists of titanium and aluminum in amounts to yield the TiAl intermetallic compound, one or more of chromium, niobium and tantalum, and incidental impurities. 
     
     
         12 . The method according to  claim 1 , wherein the titanium aluminide intermetallic composition consists of, by atomic percent, about 1.8 to about 2% chromium, up to about 2% niobium, up to about 4% tantalum, titanium and aluminum in amounts to yield the TiAl intermetallic compound, and incidental impurities. 
     
     
         13 . The method according to  claim 12 , wherein the titanium aluminide intermetallic composition contains about 46.7 to 48.9 atomic percent titanium. 
     
     
         14 . The method according to  claim 12 , wherein the titanium aluminide intermetallic composition contains about 47.3 atomic percent aluminum. 
     
     
         15 . The method according to  claim 12 , wherein the titanium aluminide intermetallic composition contains, in atomic percent, about 1.9% chromium, about 1.9 atomic percent niobium, and no intentional amount of tantalum. 
     
     
         16 . The method according to  claim 12 , wherein the titanium aluminide intermetallic composition contains, in atomic percent, about 1.8% chromium, about 0.85 atomic percent niobium, and about 1.7% tantalum. 
     
     
         17 . The method according to  claim 12 , wherein the titanium aluminide intermetallic composition contains, in atomic percent, about 2% chromium, about 4% tantalum, and no intentional amount of niobium. 
     
     
         18 . A method of processing a titanium aluminide intermetallic composition based on a TiAl intermetallic compound to yield a duplex microstructure containing equiaxed and lamellar morphologies of the gamma TiAl phase, the method comprising:
 hot isostatic pressing the titanium aluminide intermetallic composition;   cooling the titanium aluminide intermetallic composition;   heat treating the titanium aluminide intermetallic composition at a temperature of at least 1260° C. for about 2.5 to about 5 hours;   cooling the titanium aluminide intermetallic composition to a temperature of not less than 1120° C.;   holding the titanium aluminide intermetallic composition at a hold temperature of about 1150 to about 1200° C. for a duration of about two to about six hours; and then   cooling the titanium aluminide intermetallic composition to room temperature;   wherein the titanium aluminide intermetallic composition exhibits the duplex microstructure following the step of cooling the titanium aluminide intermetallic composition to room temperature.   
     
     
         19 . The method according to  claim 18 , wherein the titanium aluminide intermetallic composition is cooled after the heat treating step to a temperature of not less than 1150° C. prior to the holding step, and the hold temperature is 1150 to about 1200° C. 
     
     
         20 . The method according to  claim 18 , wherein the titanium aluminide intermetallic composition consists of titanium and aluminum in amounts to yield the TiAl intermetallic compound, one or more of chromium, niobium and tantalum, and incidental impurities.