High pressure turbine airfoil recovery device and method of heat treatment

Abstract

A fixture and method for repairing superalloy articles. The fixture ideally holds the article in place if repairs are made. An interface between the fixture and the article facilitate transfer of heat between the article and the fixture so that the article can be differentially heat treated. A portion of the article extends from the fixture. This portion of the article, which may be repaired within the fixture or may be repaired elsewhere, is solution heat treated while in the fixture so that the area extending from the fixture is solutioned, while heat is transferred from the article through the fixture, thereby preventing the temperature of the portion of the article within the fixture from being elevated so as to modify its microstructure. The solutioned portion can then be heat treated, while in the fixture, to precipitation harden it as desired.

1 . Apparatus for restoring the microstructure of a portion of an article having a thin section and a thick section, comprising:
 a heat source, the heat source to heat at least a portion of the article to a preselected temperature;   a source of cooling fluid;   a fixture for supporting the article, the fixture further comprising
 a material of high conductivity, 
 a receptacle corresponding to a surface of the article for receiving a portion of the article and providing a means for transferring heat between the article, when inserted, and the fixture, 
 an orifice having an inlet and an outlet, the inlet connected to a source of cooling fluid which removes heat from the fixture; and 
   a protective atmosphere applied around at least the portion of the article heated to the preselected temperature,   wherein cooling fluid passing through the orifice removes heat from the fixture, the heat having been transferred from the article to the fixture.   
   
   
       2 . The apparatus of  claim 1  wherein the fixture comprising a material of high conductivity includes a material selected from the group consisting of copper and copper-based alloys. 
   
   
       3 . Apparatus for solutioning a superalloy turbine blade, the turbine blade having an airfoil portion, a platform portion, a shank portion below the platform portion and a dovetail portion below the shank portion, comprising:
 means for heating the airfoil portion of the turbine blade to a first preselected temperature in the solutioning temperature range of the superalloy blade;   a source of cooling fluid;   a fixture for supporting the turbine blade, the fixture further comprising
 a material of high conductivity, 
 a receptacle having a geometry corresponding to a geometry of the turbine blade below the platform portion for providing surface contact with the turbine blade below the platform portion, when inserted therein, and wherein the airfoil portion of the turbine blade extends away from the fixture when the turbine blade is inserted into the receptacle, 
 an orifice having an inlet and an outlet, the inlet connected to the source of cooling fluid which removes heat from the fixture; and 
   a protective atmosphere surrounding at least the airfoil portion of the turbine blade when the airfoil portion is heated to the preselected temperature,   wherein the portion of the blade inserted in the receptacle is maintained at a second temperature below the first preselected temperature by the cooling fluid passing through the orifice of the fixture.   
   
   
       4 . The apparatus of  claim 3  wherein the fixture comprising a material of high conductivity includes a material selected from the group consisting of copper and copper-based alloys. 
   
   
       5 . The apparatus of  claim 3  wherein the means for heating to a first preselected temperature includes a heating means selected from the group consisting of radiant light, an induction coil and a furnace. 
   
   
       6 . The apparatus of  claim 3  wherein the source of cooling fluid is water. 
   
   
       7 . The apparatus of  claim 3  wherein the protective atmosphere is a non-reactive atmosphere. 
   
   
       8 . The apparatus of  claim 3  wherein the turbine blade further includes internal cooling passages, and the apparatus further includes means for providing cooling gas to the internal cooling passages. 
   
   
       9 . A weld repaired differentially solution treated and aged superalloy turbine blade, comprising:
 a microstructure having a preferred crystallographic orientation;   an airfoil portion, a platform portion, a shank portion below the platform portion and a dovetail portion below the shank portion;   an area of weld repair in the airfoil portion;   the portion of the blade below the platform portion characterized by an as-cast microstructure having a substantial absence of recrystallization; and   wherein the airfoil portion has a substantially preselected uniform size and distribution of γ′ precipitates further characterized by a substantial absence of rafting and wherein the area of weld repair and a heat affected zone adjacent to the area of weld repair are characterized by a substantial absence of rafting.   
   
   
       10 . The weld repaired superalloy turbine blade of  claim 9  wherein the preferred microstructure of the blade is selected from the group consisting of a single crystal grain and directionally solidified columnar grains. 
   
   
       11 . The weld repaired superalloy turbine blade of  claim 9  wherein the area of weld repair is located in the airfoil portion. 
   
   
       12 . The weld repaired superalloy turbine blade of  claim 11  wherein the area of weld repair is located in a tip region of the airfoil portion. 
   
   
       13 . A differentially solution treated superalloy turbine blade, comprising:
 a microstructure having a preferred crystallographic orientation;   an airfoil portion, a platform portion, a shank portion below the platform portion and a dovetail portion below the shank portion;   the portion of the turbine blade below the platform portion characterized by a substantially as-cast microstructure having a substantial absence of recrystallization; and   wherein the airfoil portion of the differentially solution treated turbine blade has a substantial absence of rafting.   
   
   
       14 . The differentially heat-treated turbine blade of  claim 13  further including internal cooling passageways coated with an aluminide coating, the aluminide coating substantially free of incipient melting. 
   
   
       15 . A method for using a fixture to differentially heat treat a superalloy turbine blade, comprising the steps of:
 providing a turbine blade having an airfoil portion, a platform portion, a shank portion below the platform portion and a dovetail portion below the shank portion;   providing a source of cooling fluid;   providing a fixture for supporting the turbine blade, the fixture further comprising
 a material of high conductivity, 
 a receptacle corresponding to at least a part of a blade surface below the platform portion of the turbine blade, the receptacle providing surface contact with at least the part of the blade surface below the platform surface when inserted therein so that at least the airfoil portion of the blade projects away from the fixture, 
 an orifice having an inlet and an outlet, the inlet connected to the source of the cooling fluid; 
   inserting at least a part of the blade surface below the platform portion into the receptacle of the fixture;   establishing a flow of cooling fluid from the source of cooling fluid through the orifice;   providing a heating source;   utilizing the heating source to heat the airfoil portion of the blade projecting away from the fixture; and   heating the airfoil portion of the blade to a solutioning temperature of the superalloy for a time sufficient to solution gamma prime precipitates, while maintaining at least the part of the blade below the platform in the receptacle of the fixture below the solutioning temperature, the fixture conducting heat away from the blade, and the cooling fluid conducting heat away from the fixture.   
   
   
       16 . The method of  claim 15  further including the additional steps of:
 after solutioning, heating the blade to an aging temperature below the solutioning temperature, the aging temperature and time selected to produce a uniform distribution of γ′ precipitates of a preselected size characteristic of the alloy in the solutioned portion of the blade, while not substantially affecting the size and distribution of γ′ in the portion of the blade below the platform.   
   
   
       17 . The method of  claim 15  further including the additional step of providing a protective atmosphere over at least the airfoil portion of the blade during the step of heating to a solutioning temperature. 
   
   
       18 . The method of  claim 15  wherein the additional step of providing a protective atmosphere includes providing a protective atmosphere selected from the group consisting of an inert gas and a reducing gas. 
   
   
       19 . The method of  claim 15  further including the step of applying a high temperature conductive grease between the receptacle and the part of the blade below the platform portion in the receptacle, thereby increasing conductivity between the blade and the fixture. 
   
   
       20 . The method of  claim 15  wherein the step of providing a source of cooling fluid includes providing water. 
   
   
       21 . The method of  claim 15  wherein the step of heating at least the airfoil portion of the blade to a solutioning temperature of the superalloy for a time sufficient to solution γ′ precipitates includes heating to a temperature in the range of from about 1900°-2400° F. for a time of about 0.25-24 hours. 
   
   
       22 . The method of  claim 15  wherein the step of providing a fixture comprising a material of high conductivity includes providing a fixture selected from the group consisting of copper and its alloys. 
   
   
       23 . The method of  claim 15  wherein the steps of providing a heating source and utilizing the heating source to heat the portion of the blade projecting away from the fixture includes providing quartz lamps and focusing the quartz lamps on the portion of the blade projecting away from the fixture. 
   
   
       24 . The method of  claim 15  wherein the steps of providing a heating source and utilizing the heating source to heat the portion of the blade projecting away from the fixture includes providing an induction coil and placing the induction coil around the portion of the blade projection away from the fixture. 
   
   
       25 . The method of  claim 15  wherein the step of providing a turbine blade further includes providing a turbine blade having internal cooling passageways, the step of providing a fixture further includes providing a fixture having a means for providing cooling fluid to the internal cooling passageways of the turbine blade, and the step of establishing a flow of cooling fluid further includes establishing a sufficient flow of cooling fluid through the means for providing cooling fluid to the internal cooling passageways so that the temperature of the internal passageways is maintained below an incipient melting temperature of an aluminide coating applied to the internal passageways of the superalloy turbine blade substrate. 
   
   
       26 . The method of  claim 25  wherein the step of establishing a flow of cooling fluid further includes providing a sufficient flow of cooling fluid to maintain the temperature of the internal passageways below about 2100° F. 
   
   
       27 . The method of  claim 25  wherein the step of providing a superalloy turbine blade includes providing a nickel-based superalloy turbine blade selected from the group consisting of Rene 142 and Rene N5, and wherein the step of establishing a flow of cooling fluid further includes providing a sufficient flow of cooling fluid to maintain the temperature of the internal passageways below about 2200° F.