Influence of welding current on carbide/matrix interface properties in MMCs

Metal matrix composites (MMCs) are used to increase lifetime of parts of machines in environments where they undergo severe conditions, for instance abrasive wear or impact. When a metal matrix composite is manufactured, reactions between matrix and carbides take place and a reaction zone between matrix and carbides, the interface, is formed. It is shown in the literature, that the interface has an influence on the mechanical properties of MMC. Therefore, it is important to understand, how the interface develops, whose influences on the development exist and how the interface affects the mechanical properties of the MMC. Also the composition of the interface needs to be observed. The aim of this work is to give a qualitative description of the mechanical behaviour of carbide/matrix interface in relation with the interfacial reactivity at this interface. Furthermore, a selected MMC hardfacing alloy based on 60 wt.% WC/W2C and Ni matrix was manufactured by plasma transferred arc (PTA) process at variation of welding current to estimate the composition of the interface and mechanical properties of the whole composite material. A special designed single impact test (SIT) enabled investigation of impact wear behaviour at high single loads. The evaluation of interface properties was supported by optical microscopy, SEM, XRD investigations and hardness tests. In the literature damage mechanisms under impact are pointed out to decohesion and cracking of hard phases based on interface properties. In the SIT investigations of MMC hardfacing alloy based on 60 wt.% WC/W2C and Ni matrix it can be shown that welding current is controlling the formation of the carbide/matrix interface and furthermore the dominating wear mechanisms under high single loads in SIT.