Process for complex transient liquid phase sintering of powder metal

Abstract

A process is provided wherein a metal powder of iron or low alloy steel is mixed with a lubricant having a characteristic of becoming liquid under pressure and of evaporating under a sintering temperature and at least one liquid phase former to form a mixture. The mixture is compressed at a pressure sufficient to liquefy and uniformly distribute the lubricant within the compressed mixture with the lubricant effecting a uniform distribution of the liquid phase former on the particles of the metal powder. Upon sintering, the lubricant is evaporated and driven off and a liquid phase sintering of the liquid phase former with the particles of the metal powder occurs to obtain a product having a density of 99+% of theoretical density.

1 . A process comprising the steps of 
 mixing particles of a metal powder with a lubricant having a characteristic of becoming liquid under pressure and of evaporating under a sintering temperature and at least one liquid phase former to form a mixture;    compressing the mixture at a pressure sufficient to liquefy and uniformly distribute the lubricant within the compressed mixture with said lubricant effecting a uniform distribution of said liquid phase former on said particles of metal powder; and    sintering the compressed mixture at a sintering temperature sufficient to evaporate and drive off said lubricant and to effect a liquid phase sintering of said liquid phase former with said particles of metal powder to obtain a compressed and sintered product having a density of 99+% of theoretical density.    
     
     
         2 . A process as set forth in  claim 1  wherein said metal powder is a ferrous metal powder.  
     
     
         3 . A process as set forth in  claim 1  wherein said lubricant is one of APEX PS1000b, lauric acid and Johnson's Floor Wax.  
     
     
         4 . A process as set forth in  claim 1  wherein said liquid phase former is at least one of synthetic graphite, nickel, boron, phosphorous and compounds of boron and phosphorous.  
     
     
         5 . A process as set forth in  claim 1  wherein said mixture is compressed under a compaction pressure of 35 to 70 tons per square inch.  
     
     
         6 . A process as set forth in  claim 1  wherein said mixture is compressed through high velocity compaction.  
     
     
         7 . A process as set forth in  claim 1  wherein said mixture is compressed under a compaction pressure greater than 45 tons per square inch.  
     
     
         8 . A process as set forth in  claim 1  wherein said compressed mixture is sintered at a temperature in the range of from 2070 to 2500° with the preferred range being 2300 to 2500 F.  
     
     
         9 . A process as set forth in  claim 1  wherein said compressed mixture is sintered at a temperature in the range of from 2300 to 2500° for a time of from 10 to 60 minutes.  
     
     
         10 . A process as set forth in  claim 1  wherein said step of compressing includes placement of the mixture in a tool whereby during compressing of the mixture into a green compact the liquefied lubricant forms a liquid film between the tool and the mixture to cause a green compact with a uniform density gradient to be obtained.  
     
     
         11 . A product made in accordance with the process of  claim 1 .  
     
     
         12 . A powder metal product having a density of 99+% of theoretical.  
     
     
         13 . A powder metal product as set forth in  claim 12  having a uniform density gradient throughout the product.  
     
     
         14 . A powder metal product as set forth in  claim 12  characterized in being formed of at least one of iron and low alloy steel finer than 100 mesh and a liquid phase former having a characteristic of forming a liquid phase during sintering and of becoming part of the final product after sintering.  
     
     
         15 . A powder metal product as set forth in  claim 14  characterized in that said liquid phase former is one of nickel, phosphorous, boron, a compound of boron and a compound of phosphorous and is finer than 20 microns.  
     
     
         16 . A powder metal product as set forth in  claim 14  characterized in that said liquid phase former is one of nickel, phosphorous, boron, a compound of boron and a compound of phosphorous and is finer than 10 microns.  
     
     
         17 . A powder metal product as set forth in  claim 14  characterized in that said liquid phase former is synthetic graphite and is finer than 10 microns.  
     
     
         18 . A powder metal product as set forth in  claim 14  characterized in that said liquid phase former is synthetic graphite and is finer than 2 microns.