Hard metal body with hardness gradient, such as punching tools

Abstract

The invention relates to a method for the production of a body made of hard metal, consisting of a hard compound A and a binder B, wherein pulverulent A and B, or an optionally precompacted article that contains A and B, are introduced into a container and the material containing A and B is compacted in order to increase the relative density (RD) to a value that is higher than 70% of the theoretical maximum density (TMD). The invention further relates to a body of hard metal comprising a hard compound A and a binder B, the mass ratio of A:B gradually changing over a cross-section of the body in order to impart to said body different mechanical properties in one zone Za or to one end (T) and hardness in one zone Zb or to another end (H). The invention also relates to the use of dynamic compaction techniques for the production of such bodies.

1 . Method for the production of a body made of hard metal, consisting of a hard compound a and a binder b, wherein 
 chosen amounts of pulverulent a and b, or of an optionally precompacted article that contains a and b in chosen amounts, are introduced into a container and    the material containing a and b is subjected to compaction in one or more steps in order to increase the relative density (RD) to a value that is higher than 70% of the theoretical maximum density (TMD) with the formation of a body made of hard metal, in which 
 on the one hand at least one zone (Za) containing a relatively large amount of B and, on the other hand, at least one zone (Zb) containing a relatively small amount of B are present and  
 the amount of B gradually decreases from at least one zone Za to at least one zone Zb,  
   after which said body is optionally subjected to sintering, hot isostatic pressing (HIP) or sinter HIP.    
     
     
         2 . Method according to  claim 1 , wherein the material containing A and B is compacted to a RD value in excess of 80% TMD, preferably in excess of 90% TMD.  
     
     
         3 . Method according to  claim 1  or  2 , wherein the compaction is carried out in two steps: 
 (a) a first compaction (precompaction) to increase the RD to a value of at most 70% TMD;  
 (b) a second compaction in which the RD of the precompacted powder or article from step a) is further increased to a value above 70% TMD, preferably above 80% TMD, in particular to above 90% TMD.  
 
     
     
         4 . Method according to one or more of the preceding claims, wherein different mixtures of A and B are introduced into two or more zones of the container, the mass ratios of A:B in the two or more zones having different values.  
     
     
         5 . Method according to one or more of the preceding claims, wherein the container has an elongated shape and the container is filled with different mixtures of A and B in such a way that the quantity of binder at the one end of the shape (H) is lower than that at the other end of the shape (T).  
     
     
         6 . Method according to one or more of the preceding claims, wherein the amount of B in zone Zb is at least 1% (m/m) and the amount of B in zone Za is at most 50% (m/m), the amounts being based on the mass of the total mixture.  
     
     
         7 . Method according to one of the preceding claims, wherein the amount by mass of B, optionally gradually, increases from zone Zb to zone Za.  
     
     
         8 . Method according to one or more of the preceding claims, wherein A is chosen from the group consisting of diamond or carbides such as SiC, WC, TiC, TaC, NbC, ZrC, HfC, Cr 3 C 2  and Mo 2 C, nitrides such as TiN, HfN and BN and borides such as TiB 2  and ZrB 2 , preferably tungsten carbide, and wherein B is chosen from the group consisting of the metals Co, Cr, Ni, Fe (for example stainless steel) and alloys thereof, in particular cobalt.  
     
     
         9 . Method according to one or more of the preceding claims, wherein the compaction is carried out at a temperature at which no or virtually no mass transport of B or A takes place, preferably ambient temperature.  
     
     
         10 . Method according to one or more of the preceding claims, wherein use is made of static or (iso)dynamic compaction techniques, preferably dynamic compaction techniques such as 
 pneumomechanical uniaxial compaction;    ballistic compaction;    explosive compaction, including shock compaction, and    magnetic compaction,    for the compaction.    
     
     
         11 . Body obtainable according to the method of one or more of the preceding claims.  
     
     
         12 . Body of hard metal comprising a hard compound A and a binder B, the mass ratio of A:B changing over a cross-section of the body in order to impart to said body different mechanical properties such as, on the one hand, toughness in at least one zone Za or at at least one end (T) and, on the other hand, hardness in at least one zone Zb or at at least one other end (H), the change in the ratio of A:B being gradual.  
     
     
         13 . Body made of hard metal according to  claim 11  or  12 , comprising a punching tool.  
     
     
         14 . Use of dynamic compaction techniques as specified in  claim 10  for the production of one-piece bodies made of hard metal having at least one hard zone (Zb) or hard end (H) and at least one tough zone (Za) or tough end (T).