Infiltration of a powder metal skeleton by a similar alloy to achieve uniform composition

Abstract

In infiltrating a porous metal skeleton an infiltrant composition is used similar to that of the powder skeleton, but with the addition of a melting point depressant. The infiltrant quickly fills the skeleton. As the melting point depressant diffuses into the base powder, the liquid may undergo diffusional solidification and the material eventually homogenizes. Maintaining the infiltrant at a liquidus composition for the infiltration temperature typically ensures that the bulk composition or properties will remain uniform throughout the part, particularly in the direction of infiltration. Success of such an infiltration is enhanced by effective means of maintaining the molten infiltrant at a liquidus composition. It is also beneficial, in some cases, for the time scale of the infiltration to be much faster than the time scale of the diffusion of the melting point depressant and the subsequent solidification and homogenization. The relative rates of infiltration and diffusion/solidification rate are significantly impacted by the choice of materials system. Other factors also influence these rates. They include: selection of powder size (diameter), shape, surface roughness, and size distribution, feeding liquid from different locations, liquid feeder channels, smoothing of the part surface with fine powder and affecting the infiltrant fluid properties. Various material systems are also disclosed, as are methods of designing a process of infiltrating a part, including binary and ternary and higher component systems. Homogeneous composition may be achieved using these techniques, particularly along the direction of infiltration.

Having described the inventions, what is claimed is:  
     
         1 . A method for fabricating a substantially metal part, comprising the steps of: 
 a. providing a skeleton of interconnected adhered metal powder having a network of interconnected porosities throughout, said metal powder composed of at least two elements;    b. providing an infiltrant comprising: 
 i. the same at least two elements as are in the skeleton; and  
 ii. melting point depressant (MPD);  
   the infiltrant having a composition that is a liquidus composition for an infiltration temperature; and    c. infiltrating said skeleton with said infiltrant, at approximately said infiltration temperature, whereby essentially no erosion of said skeleton transpires.    
     
     
         2 - 13 . (Canceled)  
     
     
         14 . A method for fabricating a substantially metal part, comprising the steps of: 
 a. providing a skeleton of interconnected adhered metal powder having a network of interconnected porosities throughout, said metal powder composed of two or more elements, chosen as in step e below;    b. providing an infiltrant comprising: 
 i. the same elements as are in the skeleton; and  
 ii. melting point depressant;  
   the infiltrant having a composition that is a liquidus composition for an infiltration temperature, the liquidus composition and infiltration temperature chosen as in step e below;    c. infiltrating said skeleton at said infiltration temperature with said infiltrant in liquid form;    d. subjecting said infiltrated skeleton to conditions such that a portion of said melting point depressant diffuses from said infiltrated porosities into said metal powder, and at least partial diffusional solidification occurs; and    e. choosing said metal powder composition, melting point depressant, infiltrant composition and infiltration temperature such that during diffusional solidification of said infiltrant, relative ratios, of components other than melting point depressant, in said liquid infiltrant not yet solidified, remain substantially constant.    
     
     
         15 . The method of  claim 14 , said melting point depressant consisting essentially of a single element.  
     
     
         16 . The method of  claim 14 , said melting point depressant consisting essentially of two or more elements, all of which have similar mass transport characteristics relative to said elements of said skeleton.  
     
     
         17 . The method of  claim 14 , said step of subjecting said infiltrated skeleton to conditions such that at least partial diffusional solidification occurs comprising subjecting said infiltrated skeleton to constant temperature conditions such that at least partial isothermal solidification occurs.  
     
     
         18 . The method of  claim 14 , said step of subjecting said infiltrated skeleton to conditions such that at least partial diffusional solidification occurs comprising subjecting said infiltrated skeleton to reducing temperature conditions.  
     
     
         19 . The method of  claim 14 , said skeleton further comprising melting point depressant.  
     
     
         20 . The method of  claim 14 , said skeleton being substantially free of melting point depressant.  
     
     
         21 . The method of  claim 14 , said step of choosing comprising choosing said metal powder composition, melting point depressant, infiltrant composition and infiltration temperature such that a liquidus composition and a solidus composition of said infiltrant, that are joined by a tie line on an equilibrium phase diagram, both lie on a line of substantially constant relative proportions of non-MPD components of said infiltrant.  
     
     
         22 . The method of  claim 21 , said step of choosing comprising choosing said metal powder composition, melting point depressant, infiltrant composition and infiltration temperature such that the composition of said skeleton, lies on said line of substantially constant relative proportions of non-MPD components of said infiltrant.  
     
     
         23 - 80 . (Canceled).