Process for Obtaining Tight Components by Powder Metallurgy

Abstract

The process: includes mixing a metallic powder including iron or nickel or copper or mixtures of two or three elements thereof where the sum thereof defines at least 55% in mass of the metal matrix of the component to be produced, and a molybdenum disulfide powder as a densification agent and as a solid lubricant with a content from 3 to 30% in volume; filling a mold with the mixture and obtaining a compact presenting from 5 to 25% in volume of primary pores; and subjecting the compact to a temperature and time sufficient to allow the reaction of the molybdenum disulfide with the matrix, forming iron sulfide, nickel sulfide or copper sulfide, and the diffusion of the molybdenum in the matrix; and subjecting the compact to temperature sufficient to transform the sulfide into a liquid phase, filling the primary pores before finishing the sintering step of the compact.

1 . A process for obtaining tight components by powder metallurgy, characterized in that it comprises the steps of:
 i) mixing a metallic powder selected from any of the elements defined by iron, nickel, copper and mixtures of two or three of these elements, as long as the content of the element or mixture thereof defines at least 55% of the mass of the metal matrix of the component, and a molybdenum disulfide powder as a densification agent and as a solid lubricant with a content varying between 3 and 30% in volume;   ii) homogenizing the mixture obtained in the previous step;   iii) filling the cavity of a mold, by compaction of the homogenized mixture, until achieving a compact resistant to handling and presenting between 5 to 25% in volume of primary pores;   iv) subjecting the compact to a temperature and period of time sufficient to allow the reaction of the molybdenum disulfide with the metallic powder which forms the matrix of the component to be produced, forming at least one of iron sulfide, nickel sulfide and copper sulfide, and the diffusion of the molybdenum left from the reaction in the metallic powder which forms the matrix;   v) subjecting the compact, with the already reacted molybdenum disulfide, to a temperature sufficient to transform the sulfide into a liquid phase filling the primary pores before finishing the sintering step of the compact.   
     
     
         2 . The process, as set forth in  claim 1 , characterized in that the powder material which forms the metal matrix of the compact further comprises at least one of the alloy elements selected from iron, nickel, copper, chrome, molybdenum, niobium, manganese, phosphorus, carbon, vanadium, silicon and sulfur. 
     
     
         3 . The process, as set forth in  claim 2 , characterized in that the powder material which forms the metal matrix of the compact contains at least one of the alloy elements in individual contents varying between 0.01 and 20% in mass of the material of the metal matrix. 
     
     
         4 . The process, as set forth in  claim 1 , characterized in that the powder material which forms the metal matrix of the compact presents a particle size (d 90  measured by laser granulometry) between 10 and 180 μm. 
     
     
         5 . The process, as set forth in  claim 1 , characterized in that the powder of the densification agent presents a particle size (d 90  measured by laser granulometry) between 10 and 60 μm. 
     
     
         6 . The process, as set forth in  claim 1 , characterized in that the step of compacting the powder mixture inside the mold is carried out under a pressure of 300 to 800 MPa. 
     
     
         7 . The process, as set forth in  claim 1 , characterized in that the temperature of reaction of the molybdenum disulfide with the element of the metal matrix is greater than 750° C., but lower than the sintering temperature of the metal matrix. 
     
     
         8 . The process, as set forth in  claim 1 , characterized in that the sintering time is from 5 to 180 minutes, as a function of the lower or higher amount (% content in mass) of the densification agent added to the initial powder mixture. 
     
     
         9 . The process, as set forth in  claim 1 , characterized in that it further comprises the additional steps of: adding at least one additional solid lubricant to the mixture of the element which forms the metal matrix with the molybdenum disulfide, before the step of homogenizing the mixture; and subjecting the compact to a single sintering thermal cycle, using a reducing atmosphere, in order to eliminate possible oxides on the surface of the powders, maintaining a temperature sufficient to cause “the vaporization of the” additional solid lubricant, and for a time necessary to promote the extraction of the additional solid lubricant and the formation of respective secondary pores in the compact, before subjecting the latter, already devoid of the additional solid lubricant, to the steps of reaction of the molybdenum disulfide, of liquefying the iron sulfide, the copper sulfide or the nickel sulfide into a liquid phase of filling the intercommunicating primary pores and secondary pores, and of sintering the metallic powder of the matrix. 
     
     
         10 . The process, as set forth in  claim 9 , characterized in that the solid lubricant powder presents a particle size (d 90  measured by laser granulometry) between 1.0 e 60 μm. 
     
     
         11 . The process, as set forth in  claim 9 , characterized in that the additional solid lubricant used for forming the compact comprises at least one of the elements selected from zinc stearate, amides, manganese sulfide, graphite and hexagonal boron nitride.