Method of making a closed porosity surface coating on a low density preform

Abstract

A method of making a low density part with a closed porosity surface coating is formed by applying, to a porous powder preform, a coating of powder finer than that of the preform which is sinterable to a near full density below the melting temperature of the powder; and heating the coated preform to sinter the coating to form a near full density, gas impermeable, closed porosity surface coating on the preform.

What is claimed is:  
     
         1 . A method of making a low density part with a closed porosity surface coating comprising: 
 applying, to a porous powder preform, a coating of powder finer than that of the preform which is sinterable to a near full density below the melting temperature of the powder; and    heating the coated preform to sinter the coating to form a near full density, gas impermeable, closed porosity surface coating on the preform.    
     
     
         2 . The method of    claim 1    further including applying an increased pressure to the closed porosity coating for transmitting the force of the pressure through the coating to consolidate the porous powder preform to a predetermined density.  
     
     
         3 . The method of    claim 2    in which the increased pressure includes gas pressure.  
     
     
         4 . The method of    claim 2    in which the preform is consolidated to near full density.  
     
     
         5 . The method of    claim 1    in which the step of applying includes adding the metal powder to a carrier and applying the carrier to the preform.  
     
     
         6 . The method of    claim 5    in which the carrier includes a binder for aiding the powder in adhering to the preform.  
     
     
         7 . The method of    claim 1    in which applying includes brushing the powder onto the preform.  
     
     
         8 . The method of    claim 1    in which applying includes dipping the preform into the powder.  
     
     
         9 . The method of    claim 1    in which applying includes spraying the powder onto the preform.  
     
     
         10 . The method of    claim 9    in which the powder is melted and sprayed on as molten droplets.  
     
     
         11 . The method of    claim 1    further including placing the powder coated preform in a vacuum furnace and reducing the pressure to remove any gas from the porous preform prior to heating.  
     
     
         12 . The method of    claim 1    in which the powder is spherical.  
     
     
         13 . The method of    claim 1    in which the coating of powder is the same material as the preform.  
     
     
         14 . A method of making a high density part from a low density part comprising: 
 applying, to a porous powder preform, a coating of powder finer than that of the preform which is sinterable to a near full density below the melting temperature of the powder coating;    heating the powder coated preform to sinter the coating to form a near full density, gas impermeable, closed porosity surface coating on the preform; and    applying increased pressure to the closed porosity coating for transmitting the force of the pressure through the coating to consolidate the porous powder preform to a predetermined density.    
     
     
         15 . The method of    claim 14    in which the increased pressure includes gas pressure.  
     
     
         16 . The method of    claim 14    in which the predetermined density is near full density.  
     
     
         17 . The method of    claim 14    in which the step of applying includes adding the metal powder to a carrier and applying the carrier to the preform.  
     
     
         18 . The method of    claim 17    in which the carrier includes a binder for aiding the powder in adhering to the preform.  
     
     
         19 . The method of    claim 14    in which applying includes brushing the powder onto the preform.  
     
     
         20 . The method of    claim 14    in which applying includes dipping the preform into the powder.  
     
     
         21 . The method of    claim 14    in which applying includes spraying the powder onto the preform.  
     
     
         22 . The method of    claim 21    in which the powder is melted and sprayed on as molten droplets.  
     
     
         23 . The method of    claim 14    further including placing the coated preform in a vacuum furnace and reducing the pressure to remove any gas from the porous preform prior to heating.  
     
     
         24 . The method of    claim 14    in which the powder is spherical.  
     
     
         25 . The method of    claim 14    in which the coating of powder is the same material as the preform.  
     
     
         26 . A method of making a metallic part with a closed porosity surface coating comprising: 
 applying, to a metallic part, a coating of powder sinterable to a near full density below the melting temperature of the powder; and    heating the coated part to sinter the powder coating to form a near full density, gas impermeable, closed porosity surface coating.    
     
     
         27 . The method of    claim 26    further including applying an increased pressure to the closed porosity surface coating for transmitting the force of the pressure through the coating to consolidate the porous powder preform to a predetermined density.  
     
     
         28 . The method of    claim 27    in which the increased pressure includes gas pressure.  
     
     
         29 . The method of    claim 27    in which the preform is consolidated to near full density.  
     
     
         30 . The method of    claim 26    in which the step of applying includes adding the metal powder to a carrier and applying the carrier to the preform.  
     
     
         31 . The method of    claim 30    in which the carrier includes a binder for aiding the powder in adhering to the preform.  
     
     
         32 . The method of    claim 26    in which applying includes brushing the powder onto the preform.  
     
     
         33 . The method of    claim 26    in which applying includes dipping the preform into the powder.  
     
     
         34 . The method of    claim 26    in which applying includes spraying the powder onto the preform.  
     
     
         35 . The method of    claim 33    in which the powder is melted and sprayed on as molten droplets.  
     
     
         36 . The method of    claim 26    further including placing the coated preform in a vacuum furnace and reducing the pressure to remove any gas from the porous preform prior to heating.  
     
     
         37 . The method of    claim 26    in which the powder is spherical.  
     
     
         38 . The method of    claim 26    in which the coating of powder is the same material as the preform.  
     
     
         39 . A low density powder metal near net shape part with a closed porosity coating produced by: 
 applying, to a porous powder preform, a coating of powder finer than that of the preform which is sinterable to a near full density below the melting temperature of the powder; and    heating the coated preform to sinter the coating to form a near full density, gas impermeable, closed porosity surface coating on the preform.    
     
     
         40 . A near net shape part comprising: 
 a porous metal powder preform; and    a fine metal powder coating disposed on said preform, the metal powder coating sintered below the melting temperature of the powder coating to form a full density, gas impermeable closed porosity coating on the preform.    
     
     
         41 . The near net shape part of    claim 40    in which the metal preform had a near full density.  
     
     
         42 . A method of making a near net shape full density coating comprising: 
 applying a powder coating to a powder metal preform, the powder coating sinterable to full density; and    heating the coated preform to sinter the coating to form a closed porosity, gas impermeable near net shape coating.    
     
     
         43 . The method of    claim 42    in which the powder of the coating is finer than that of the preform.  
     
     
         44 . A method of making a low density part with a gas impermeable coating comprising: 
 applying, to a porous powder preform, a coating of powder finer than that of the preform and having a lower melting point than the preform; and    heating the powder coated preform to melt the coating such that the coating reacts with the preform to form a near full density, gas impermeable, closed porosity surface coating on the preform.