Metal powder composition for laser sintering

Abstract

A powder blend for use in laser sintering and a method for forming tough, strong, wear-resistant, corrosion-resistant infiltrated metal products are provided. The powder blend comprises a steel alloy, a polymeric binder and a high melting temperature fine particulate which are blended together, then applied layer by layer to a working surface in a laser sintering system, exposed a layer at a time to fuse together the powder until a green part of high strength is formed, and then the green part is infiltrated with a metal infiltrant in a non-reducing gas atmosphere at an effective temperature for an effective period of time. The preferred steel is a mild steel alloy.

What is claimed:  
     
         1 . A powder blend for use in a laser sintering process comprising a steel alloy selected from the group consisting of a mild steel alloy, a carbon steel and a stainless steel, a polymeric binder and a high melting temperature fine particulate.  
     
     
         2 . The powder blend according to  claim 1  wherein the steel alloy ranges in size from less than about 90 microns to about 4 microns.  
     
     
         3 . The powder blend according to  claim 2  wherein the steel alloy ranges in size from less than about 75 microns to about 8 microns.  
     
     
         4 . The powder blend according to  claim 2  wherein the steel alloy is less than about 45 microns.  
     
     
         5 . The powder blend according to  claim 1  wherein the steel alloy is spherical.  
     
     
         6 . The powder blend according to  claim 2  wherein the high melting temperature fine particulate has a particle size less than about 10 microns.  
     
     
         7 . The powder blend according to  claim 6  wherein the high melting temperature fine particulate has a particle size less than about 2 microns.  
     
     
         8 . The powder blend according to  claim 7  wherein the high melting temperature fine particulate comprises greater than about 5 weight percent and less than about 15 weight percent of the powder blend.  
     
     
         9 . The powder blend according to  claim 8  wherein the high melting temperature fine particulate comprises about 8 weight percent of the powder blend.  
     
     
         10 . The powder blend according to  claim 1  wherein the polymeric binder is a thermoplastic or a thermoset.  
     
     
         11 . The powder blend according to  claim 1  wherein the polymeric binder is selected from the group consisting of polyethylene, polypropylene, polyacetal, polymethacrylate, polyvinylacetate, nylon, wax, phenolic and combinations thereof.  
     
     
         12 . The powder blend according to  claim 11  wherein the polymeric binder is nylon.  
     
     
         13 . The powder blend according to  claim 12  wherein the nylon is one selected from the group consisting of polymers and co-polymers of nylon 6, nylon 9, nylon 10, nylon 11, and nylon 12.  
     
     
         14 . The powder blend according to  claim 1  further comprising a flow agent.  
     
     
         15 . The powder blend according to  claim 14  wherein the flow agent is fumed silica.  
     
     
         16 . A method of forming a tough, strong, wear-resistant, corrosion-resistant, infiltrated metal product comprising the steps of: 
 a. mixing together a powder blend comprising a steel alloy selected from the group consisting of a mild steel alloy, a carbon steel and a stainless steel, a polymeric binder and a high melting temperature fine particulate;    b. applying a layer of the powder blend to a working surface in a laser sintering system;    c. exposing the layer of the powder blend to heat energy to fuse together the steel alloy and high melting temperature fine particulate by the melting and subsequent rehardening of the binder material;    d. applying a new layer of powder blend and exposing the new layer of powder blend in sequential fashion repeatedly until a three-dimensional green metal part is formed; and    e. infiltrating a green metal part with metal infiltrant in a gas atmosphere at an effective temperature for an effective time period.    
     
     
         17 . The method according to  claim 16  wherein using a powder blend comprising about 88.75 to about 92.75 weight percent mild steel alloy; 
 about 6 to about 9 percent tungsten carbide, and  
 about 1.25 to about 2.25 weight percent polymer binder.  
 
     
     
         18 . The method according to  claim 16  further comprising using copper and/or copper containing alloys as a metal infiltrant.  
     
     
         19 . The method according to  claim 18  further comprising using a gas selected from the group consisting of nitrogen, argon, or a nitrogen argon blend as the gas atmosphere during infiltration.  
     
     
         20 . The method according to  claim 19  using nitrogen as the gas atmosphere during infiltration.  
     
     
         21 . The method according to  claim 19  further comprising performing the infiltrating using an infiltration cycle having a peak temperature of about 1070° C.  
     
     
         22 . The method according to  claim 16  further comprising exposing the infiltrated green metal part to a heat treatment cycle.  
     
     
         23 . The method according to claims  20  further comprising using a fine grit alumina packing medium as a support material to encase the green metal part during infiltration.  
     
     
         24 . The method according to  claim 17  further comprising using a powder blend having about 8 weight percent high melting temperature fine particulate, 
 about 1.6 to about 2.1 weight percent nylon binder, and  
 the remainder a mild steel alloy.  
 
     
     
         25 . The method according to  claim 24  further comprising deagglomerating the mild steel alloy to a range in size from less than about 90 microns to about 4 microns.  
     
     
         26 . The method according to  claim 24  further comprising deagglomerating the mild steel alloy to a range in size from less than about 75 microns to about 8 microns.  
     
     
         27 . The method according to  claim 25  further comprising deagglomerating the high melting temperature fine particulate.  
     
     
         28 . The method according to  claim 27  further comprising using a high melting temperature fine particulate having a particle size less than about 10 microns.  
     
     
         29 . The method according to  claim 22  further comprising performing the heat treatment cycle having a peak temperature of about 840° C. for at least one hour, quenching the infiltrated part with room temperature nitrogen to reduce the part temperature over an effective time, sub-cooling the part to about −79° C. over at least a 90 minute period, return the part to room temperature, and temper the part for about 3 hours at about 163° C.  
     
     
         30 . The method according to  claim 16  further comprising prior to infiltrating, absorbing nitrogen into a mild steel alloy in the green metal part.  
     
     
         31 . The method according to  claim 30  further comprising prior to infiltrating, maintaining the green metal part at a temperature in excess of about 850° C. and less than about 900° C. for about 4 to about 6 hours in a nitrogen atmosphere.  
     
     
         32 . The powder blend according to  claim 9  wherein the high melting temperature fine particulate is tungsten carbide.  
     
     
         33 . The method according to  claim 28  further comprising using tungsten carbide as the high melting temperature fine particulate.