Auger studies on the segregation of trace elements in cemented carbides and their basic powders

Trace elements can affect the mechanical and technological properties of cemented carbides, and subsequently the service life of the cutting tools. Therefore, within the European Concerted Research Action COST 503, Project D34 was concerned with investigations on the segregation behaviour of different dope elements, among them Ca, Si, Al, P, S in 1,5 mym WC powders, in the mixed carbides (W,Ti) C, (Nb,Ta) C, and in Co powder by means of Auger Electron Spectroscopy (AES). The topochemistry of those powders in characterized by depth profiling and mapping of the elements and the resulting enrichment factors are discussed. In situ AES investigations of the fracture surfaces of sintered three phase cemented carbides prove that, of all dope elements, only P segregates to grain boundaries and interfaces in fractions of a monolyer. However, neither this P-segregation nor the homogeneous distribution of the trace elements have a significant influence on the mechanical and technological behaviou r of the cemented carbides in laboratory tests. Only the presence of large heterogeneous CaS inclusions was found to affect the fracture strength in bending tests considerably.