Composite core for casting processes, and processes of making and using the same

Abstract

A composite ceramic core that, in combination with a shell mold, is suitable for use in a casting process to produce metal alloy components. The core and casting process make use of a highly leachable interior layer in combination with an exterior layer that is less reactive than the interior layer in the presence of common alloying elements. The interior layer contains at least one hollow channel that allows a point of entry for a leaching solution, as well as exit for gaseous byproducts generated during the casting process.

1 : A core for use in combination with a shell mold to cast a hollow component from a reactive metal alloy, the core comprising:
 an outermost surface and at least a first internal channel within the core that defines an innermost surface of the core;   an interior layer formed of a sintered particulate material having an inner surface and an outer surface, the inner surface of the interior layer being the innermost surface of the core, the interior layer sintered particulate material has a high leachability; and   at least one exterior layer on the outer surface of the interior layer so that the interior layer is entirely internal of the exterior layer and the outermost surface of the core is entirely defined by the exterior layer, the exterior layer being formed of a sintered particulate material that is relatively inert to the reactive metal alloy and less reactive with the reactive metal alloy than the sintered particulate material of the interior layer, wherein the first internal channel extends through the interior layer and through the exterior layer to define an opening of the first internal channel at the outermost surface of the core, and   wherein the interior layer is predominately silica and the exterior layer is predominately alumina.   
     
     
         2 : (canceled) 
     
     
         3 : The core according to  claim 1 , wherein the outer surface of the interior layer is defined at an interface between the interior layer and the exterior layer, the thickness of the interior layer being about 60% to about 70% of local core thickness. 
     
     
         4 : The core according to  claim 1 , wherein the exterior layer has a thickness of about 30% to about 40% of local core thickness. 
     
     
         5 : The core according to  claim 1 , further comprising interlocking features in the outer surface of the interior layer that interlock and retain the exterior layer on the interior layer. 
     
     
         6 : The core according to  claim 5 , wherein the interlocking features protrude at the outer surface of the interior layer and into the exterior layer. 
     
     
         7 : The core according to  claim 5 , wherein the interlocking features comprise an array of protuberances and/or depressions that protrude or are recessed at least 20% of a local thickness of the exterior layer. 
     
     
         8 : A process of casting a reactive metal alloy to form the component using the core according to  claim 1 , the method comprising:
 forming the core;   providing a shell mold that surrounds the core so as to define a cavity therebetween;   introducing a molten quantity of the reactive metal alloy into the cavity of the shell mold;   allowing the molten quantity to cool and solidify to form the component;   removing the shell mold; and then leaching the core from the component by introducing a leaching solution into the first internal channel within the core, the leaching solution removing the interior layer of the core and leaving a hollow shell defined by a residual portion of the exterior layer of the core.   
     
     
         9 : The process according to  claim 8 , wherein the step of forming the core comprises forming the interior layer over a preformed body such that the preformed body is within the first internal channel. 
     
     
         10 : The process according to  claim 9 , further comprising removing the preformed body prior to introducing the molten quantity of the reactive metal alloy into the cavity of the shell mold. 
     
     
         11 : The process according to  claim 9 , wherein the preformed body is formed of graphite and is oxidized during the removing step. 
     
     
         12 : The core according to  claim 1 , wherein the first internal channel comprises a main trunk that defines the opening at the outermost surface of the core and multiple branches that extend from the main trunk and are entirely defined in the interior layer. 
     
     
         13 : The process according to  claim 9 , wherein the interior layer has a thickness between an inner surface of the interior layer defined by the channel and an outer surface of the interior layer defined at an interface between the interior layer and the exterior layer, the thickness of the interior layer being about 60% to about 70% of local core thickness. 
     
     
         14 : The process according to  claim 9 , wherein the exterior layer has a thickness of about 30% to about 40% of local core thickness. 
     
     
         15 : The process according to  claim 9 , wherein the interior layer is formed of a particulate material having a particle size of about 120 mesh prior to being sintered. 
     
     
         16 : The process according to  claim 9 , wherein the exterior layer is formed of a particulate material having a particle size of about 170 mesh and is finer than the particle size of the particulate material of the interior layer. 
     
     
         17 : The process according to  claim 9 , wherein the interior layer is predominately silica and the exterior layer is predominately alumina. 
     
     
         18 : The process according to  claim 9  wherein the interior layer is formed to have interlocking features on the surface thereof to retain the exterior layer on the interior layer. 
     
     
         19 : The process according to  claim 18 , wherein the interlocking features comprise an array of ribs with heights of about 5% to about 10% of local thickness of the exterior layer. 
     
     
         20 : The process according to  claim 18 , wherein the interlocking features comprise an array of protuberances and/or depressions with heights of about 10% to about 20% of local thickness of the exterior layer.