High thermal gradient casting with tight packing of directionally solidified casting

Abstract

Method for forming directionally solidified articles in tightly packed mold cavities withdrawn into liquid metal cooling bath. The withdrawal rate and the spacing between adjacent mold cavities cooperate to provide a high thermal gradient. The cast articles exhibit primary dendrite arm spacing of between about 6 to about 12 mils (about 150-300 microns).

1 . A method of making a plurality of directionally solidified articles comprising:
 adding a molten superalloy metal to a plurality of cavities in a mold in a heated zone, each cavity being defined at least in part by an associated mold wall spaced at a predetermined minimum spacing from an adjacent cavity, wherein each of the cavities is shaped to form at least one cast article,   withdrawing the mold with the molten superalloy metal from the heated zone into a liquid metal cooling tank at a predetermined withdrawal rate;   wherein the withdrawal rate and the spacing cooperate to provide a thermal gradient sufficient to solidify the molten metal to form a plurality of directionally solidified cast articles each having primary dendrite arm spacing of between about 6 to about 12 mils (about 150 to about 300 microns).   
   
   
       2 . The method according to  claim 1  wherein the mold includes at least a first cavity group located in an outer portion of the mold and a second cavity group located in an inner portion of the mold. 
   
   
       3 . The method according to  claim 1  wherein the minimum spacing between adjacent cavities is between about ⅛ to about ⅞ inch (about 3 to about 22 mm). 
   
   
       4 . The method according to  claim 1  wherein the withdrawal rate is greater than 12 to about 50 in/hr. (greater than 30 to about 127 cm/hr). 
   
   
       5 . The method according to  claim 4  wherein the withdrawal rate is selected from greater than about 12 to about 20 in/hr (greater than about 30 to about 50 cm/hr), about 16 to about 30 in/hr (about 40 to about 76 cm/hr), about 20 to about 30 in/hr (about 50 to about 76 cm/hr), and about 16 to about 50 in/hr (about 40 to about 127 cm/hr). 
   
   
       6 . The method according to  claim 1  wherein adding the molten superalloy metal includes adding a superalloy metal comprising, in weight percent:
 Al 6.2, Ta 6.5, Cr 7, W 5, Mo 1.5, Re 3, Co 7.5, C 0.05, B 0.004, Hf 0.15, balance nickel and incidental impurities.   
   
   
       7 . The method according to  claim 1  wherein at least one of the mold cavities includes an upper and lower molding region, wherein each molding region is shaped to form a cast article. 
   
   
       8 . The method according to  claim 1  wherein the minimum spacing between adjacent cavities is between about ⅛ to about ⅞ inch (about 3 to about 22 mm) and the withdrawal rate is at least one of about 12 to about 20 in/hr (about 30 to about 50 cm/hr), about 16 to about 30 in/hr (about 40 to about 76 cm/hr), and about 20 to about 30 in/hr (about 50 to about 76 cm/hr), and about 16 to about 50 in/hr (about 40 to about 127 cm/hr). 
   
   
       9 . The method according to  claim 1  wherein the withdrawal rate and the spacing cooperate to provide a thermal gradient sufficient to solidify the molten metal to form the plurality of directionally solidified cast articles each having primary dendrite arm spacing of between about 8 to about 10 mils (about 200 to about 250 microns). 
   
   
       10 . The method according to  claim 1  wherein:
 adding the molten superalloy metal includes adding a superalloy metal comprising, in weight percent: Al 6.2, Ta 6.5, Cr 7, W 5, Mo 1.5, Re 3, Co 7.5, C 0.05, B 0.004, Hf 0.15, balance nickel and incidental impurities;   the minimum spacing between adjacent cavities is between about ⅛ inch to about ⅞ inch (about 3 mm to about 22 mm) and the withdrawal rate is at least one of about 12 to about 20 inches/hour (about 30 to about 50 cm/hr), about 16 to about 30 inches/hour (about 40 to about 76 cm/hr), and about 20 to about 30 inches/hour (about 50 to about 76 cm/hr), and about 16 to about 50 in/hr (about 40 to about 127 cm/hr); and   the withdrawal rate and the spacing cooperate to provide a thermal gradient to solidify the molten metal to form the plurality of directionally solidified cast articles each having primary dendrite arm spacing of between 6 to about 10 mils (about 150 to about 250 microns).   
   
   
       11 . A directionally solidified article prepared by the method according to  claim 1 . 
   
   
       12 . The directionally solidified article according to  claim 11  comprising a blade for a gas turbine engine. 
   
   
       13 . A mold utilized in the formation of a plurality of directionally solidified articles prepared by the method according to  claim 1 . 
   
   
       14 . A method for reducing solidification defects in a directionally solidified cast article comprising a high-refractory nickel base superalloy, the method comprising:
 adding a molten high-refractory nickel base superalloy metal to at least one cavity in a mold in a heated zone, wherein the cavity is shaped to form at least one cast article;   withdrawing the mold with the molten superalloy metal from the heated zone into a liquid metal cooling tank at a predetermined withdrawal rate;   wherein the withdrawal rate is sufficient to provide a thermal gradient to solidify the molten metal to form at least one directionally solidified cast article having primary dendrite arm spacing of between about 6 to about 12 mils (about 150 to about 300 microns); and   wherein the primary dendrite arm spacing provides a reduction in solidification defects in the at least one cast article relative to an amount of solidification defects in a cast article comprising a comparable high-refractory nickel base superalloy formed using a Bridgman technique.   
   
   
       15 . A cast article comprising:
 a directionally solidified high refractory nickel base superalloy and exhibiting a primary dendrite arm spacing of from about 6 to about 12 mils.   
   
   
       16 . The cast article according to  claim 13  comprising a high pressure gas turbine engine blade.