Method of removal of cores from niobium-based part

Abstract

A system and method for removing an yttria-based core material from a part of a niobium-based material is presented. The yttria-based core material is rapidly removed from the niobium-based part without detrimentally affecting the properties or surface of the part.

1 . A method of removing an yttria-based core from a niobium-based part, comprising the step of: 
 contacting the yttria-based core with an effective amount of a composition which comprises at least one acid selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid, nitric/phosphoric acid, sulfuric acid, and acetic acid.    
   
   
       2 . The method of  claim 1  further comprising the step of heating the composition to a temperature effective to dissolve the yttria-based core.  
   
   
       3 . The method of  claim 2  wherein the temperature is the boiling temperature of the acid composition at a selected pressure.  
   
   
       4 . The method of  claim 1  further comprising the step of agitating an interface of the acid composition with the yttria-based core.  
   
   
       5 . The method of  claim 1  wherein the niobium-based part comprises a niobium silicide material.  
   
   
       6 . The method of  claim 1  wherein the yttria-based core comprises a material selected from the group consisting of yttria, and oxides of at least one of magnesium, calcium, strontium, niobium, silicon, hafnium, zirconium, titanium, a rare earth metal of the lanthanide series, and combinations thereof.  
   
   
       7 . A method of casting a part, comprising the steps of: 
 positioning an yttria-based core within a mold;    introducing a molten niobium-based alloy into the mold to cast a part; and    dissolving the yttria-based core with at least one acid selected from the group consisting of acetic acid, hydrochloric acid, nitric acid, phosphoric acid, nitric/phosphoric acid, and sulfuric acid.    
   
   
       8 . The method of  claim 7  further comprising the step of forming the yttria-based core from a material selected from the group consisting of yttria, and oxides of at least one of magnesium, calcium, strontium, niobium, silicon, hafnium, zirconium, titanium, and a rare earth metal of the lanthanide series.  
   
   
       9 . The method of  claim 7  further comprising maintaining a temperature of the acid between about 50 degrees Celsius and about a boiling temperature of the acid.  
   
   
       10 . The method of  claim 7 , wherein the niobium-based alloy comprises a niobium-silicide.  
   
   
       11 . The method of  claim 7  comprising dissolving the yttria-based core with at least one of about 5% to about 91% concentration nitric acid, about 2% to about 37% concentration HCl acid, about 50% to about 85% concentration phosphoric acid, about 5% to about 30% concentration sulfuric acid, and about 30% to about 90% concentration acetic acid.  
   
   
       12 . The method of  claim 7  wherein the part is a turbine component.  
   
   
       13 . The method of  claim 7 , wherein the yttria-based core is dissolved by submerging the part in the acid to dissolve the yttria-based core.  
   
   
       14 . The method of  claim 7  further comprising forming the yttria-based core to have a density between about 50% and about 100%.  
   
   
       15 . A method of forming a turbine blade comprising the steps of: 
 casting a blade having at least one passage defined by a core formed of an yttria-type material by pouring a niobium-type material into a mold; and    removing the core from the blade by contacting the core with an acid which comprises at least one acid selected from the group consisting of acetic acid, hydrochloric acid, a nitric acid, a phosphoric acid, a nitric/phosphoric acid, and a sulfuric acid.    
   
   
       16 . The method of  claim 15  wherein the yttria-type material comprises a material selected from the group consisting of yttria, and oxides of at least one of magnesium, calcium, strontium, niobium, silicon, hafnium, zirconium, titanium, and a rare earth metal of the lanthanide series.  
   
   
       17 . The method of  claim 15  further comprising selecting the acid for the acid's reactivity with the yttria-type material and the acid's non-reactivity with the niobium-type material.  
   
   
       18 . The method of  claim 15  wherein the acid comprises at least one of about 5% to about 91% concentration nitric acid, about 2% to about 37% concentration HCl acid, about 50% to about 85% concentration phosphoric acid, about 5% to about 30% concentration sulfuric acid, and about 30% to about 90% concentration acetic acid.  
   
   
       19 . The method of  claim 15  wherein the niobium-type material comprises niobium-silicide.  
   
   
       20 . The method of  claim 15  further comprising the step of agitating an interface between the acid and the yttria-type material.  
   
   
       21 . The method of  claim 15  wherein the acid is the azeotropic mixture of nitric acid.  
   
   
       22 . The method of  claim 15  wherein the acid comprises an azeotropic mixture of nitric acid and is maintained at a temperature of about 110 degrees Celsius to about the constant boiling point temperature of the azeotrope.