Slip and pressure casting of refractory metal bodies

Abstract

In various embodiments, powders with engineered particle-size distributions are slip or pressure casted to produce homogeneous parts without the need for additives such as flocculating or deflocculating agents.

What is claimed is: 
     
         1 . A method of producing a shaped part, the method comprising:
 suspending, in a liquid consisting essentially of water, a powder having a particle-size distribution d10 between 0.15 micron and 0.5 micron, d50 between 0.6 micron and 1 micron, and d90 between 2.4 microns and 3 microns, thereby forming a slip, wherein a particle-size distribution dX of Y denotes that X % of particles have a size less than Y;   introducing the slip into a mold having a shape approximately equal to a desired shape of the shaped part, the particle-size distribution of the powder (i) substantially preventing separation of the powder from the liquid by at least one of agglomeration or sedimentation and (ii) maintaining a substantially homogeneous distribution of powder particles within the liquid;   thereafter, allowing at least a portion of the liquid to drain out of the slip to produce a green body comprising the powder; and   sintering the green body to produce the shaped part.   
     
     
         2 . The method of  claim 1 , wherein the particle-size distribution of the powder is d10 of approximately 0.3 micron, d50 of approximately 0.8 micron, and d90 of approximately 2.7 microns. 
     
     
         3 . The method of  claim 1 , wherein, after sintering, the shaped part has a density between approximately 95% and approximately 99% of theoretical density. 
     
     
         4 . The method of  claim 1 , wherein, after sintering, the shaped part has a grain size between approximately 10 microns and approximately 20 microns. 
     
     
         5 . The method of  claim 1 , wherein the powder comprises one or more metals. 
     
     
         6 . The method of  claim 1 , wherein the powder comprises one or more refractory metals. 
     
     
         7 . The method of  claim 1 , wherein the powder comprises at least one of tungsten, tantalum, niobium, zirconium, molybdenum, or titanium. 
     
     
         8 . The method of  claim 1 , wherein the powder comprises tungsten. 
     
     
         9 . The method of  claim 1 , wherein the green body is sintered in hydrogen. 
     
     
         10 . The method of  claim 1 , wherein the green body is sintered at a temperature between approximately 3000° F. and approximately 5000° F. 
     
     
         11 . The method of  claim 1 , further comprising producing the powder by a process comprising:
 providing an initial powder having a particle-size distribution d10 of approximately 0.42 micron, d50 of approximately 1.8 micron, and d90 of approximately 3.8 microns;   deagglomerating a portion of the initial powder; and   blending the deagglomerated portion of the initial powder with a second portion of the initial powder.   
     
     
         12 . The method of  claim 11 , wherein the portion of the initial powder is deagglomerated by ball milling. 
     
     
         13 . The method of  claim 1 , wherein a density of the green body is between approximately 30% and approximately 40% of theoretical density. 
     
     
         14 . The method of  claim 1 , wherein the liquid consists essentially of deionized water. 
     
     
         15 . The method of  claim 1 , wherein (i) the mold is porous and (ii) substantially all of the liquid from the slip drains into the mold to form the green body. 
     
     
         16 . The method of  claim 1 , wherein neither the slip nor the mold is agitated after the slip is introduced into the mold. 
     
     
         17 . The method of  claim 1 , further comprising applying a super-atmospheric pressure to at least one of the mold or the slip during or after introducing the slip into the mold. 
     
     
         18 . The method of  claim 1 , wherein the powder is substantially homogeneously distributed within the green body. 
     
     
         19 . The method of  claim 1 , further comprising machining the shaped part to a desired size and/or shape. 
     
     
         20 . A method of producing a shaped part, the method comprising:
 suspending a powder in water without flocculating or deflocculating additives, thereby forming a slip;   substantially without separation of the powder from the water thereduring, introducing the slip into a mold having a shape approximately complementary to a desired shape of the shaped part;   thereafter, allowing at least a portion of the liquid to drain out of the slip to produce a green body comprising the powder; and   sintering the green body to produce the shaped part.   
     
     
         21 . The method of  claim 20 , wherein the powder has a particle-size distribution (i) substantially preventing separation of the powder from the water by at least one of agglomeration or sedimentation and (ii) maintaining a substantially homogeneous distribution of powder particles within the liquid. 
     
     
         22 . The method of  claim 21 , wherein the particle-size distribution is d10 between 0.15 micron and 0.5 micron, d50 between 0.6 micron and 1 micron, and d90 between 2.4 microns and 3 microns, a particle-size distribution dX of Y denoting that X % of particles have a size less than Y. 
     
     
         23 . The method of  claim 20 , wherein the powder comprises one or more metals. 
     
     
         24 . The method of  claim 20 , further comprising applying a super-atmospheric pressure to at least one of the mold or the slip during or after introducing the slip into the mold.